Patent Publication Number: US-2018048447-A1

Title: User equipments, base stations and methods

Description:
RELATED APPLICATIONS 
     This application is related to and claims priority from U.S. Provisional Patent Application No. 62/373,793, entitled “USER EQUIPMENTS, BASE STATIONS AND METHODS,” filed on Aug. 11, 2016, which is hereby incorporated by reference herein, in its entirety. 
    
    
     TECHNICAL FIELD 
     The present disclosure relates generally to communication systems. More specifically, the present disclosure relates to user equipments (UEs), base stations and methods. 
     BACKGROUND 
     Wireless communication devices have become smaller and more powerful in order to meet consumer needs and to improve portability and convenience. Consumers have become dependent upon wireless communication devices and have come to expect reliable service, expanded areas of coverage and increased functionality. A wireless communication system may provide communication for a number of wireless communication devices, each of which may be serviced by a base station. A base station may be a device that communicates with wireless communication devices. 
     As wireless communication devices have advanced, improvements in communication capacity, speed, flexibility and/or efficiency have been sought. However, improving communication capacity, speed, flexibility and/or efficiency may present certain problems. 
     For example, wireless communication devices may communicate with one or more devices using a communication structure. However, the communication structure used may only offer limited flexibility and/or efficiency. As illustrated by this discussion, systems and methods that improve communication flexibility and/or efficiency may be beneficial. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a block diagram illustrating one implementation of one or more evolved NodeBs (eNBs) and one or more user equipments (UEs) in which systems and methods for low latency radio communications may be implemented; 
         FIGS. 2A and 2B  are block diagrams illustrating a detailed configuration of an eNB and a UE in which systems and methods for low latency radio communications may be implemented; 
         FIG. 3  is a flow diagram illustrating a method by a UE; 
         FIG. 4  is a flow diagram illustrating a method by an eNB; 
         FIG. 5  is a diagram illustrating one example of a radio frame that may be used in accordance with the systems and methods disclosed herein; 
         FIG. 6  is a diagram illustrating one example of a resource grid for the downlink (DL); 
         FIG. 7  is a diagram illustrating one example of a resource grid for the uplink (UL); 
         FIG. 8  illustrates an example of a retransmission cycle of a DL transport block (DL-TB); 
         FIG. 9  illustrates an example of a retransmission cycle of a UL transport block (UL-TB); 
         FIG. 10  illustrates an example of a retransmission cycle of a DL-TB with a shortened Round Trip Time (RTT) timeline; 
         FIG. 11  illustrates an example of a retransmission cycle of a UL-TB with a shortened RTT timeline; 
         FIG. 12  illustrates various components that may be utilized in a UE; 
         FIG. 13  illustrates various components that may be utilized in an eNB; 
         FIG. 14  is a block diagram illustrating one implementation of a UE in which systems and methods for low latency radio communications may be implemented; and 
         FIG. 15  is a block diagram illustrating one implementation of an eNB in which systems and methods for low latency radio communications may be implemented. 
     
    
    
     DETAILED DESCRIPTION 
     A user equipment (UE) is described. A higher-layer processor is configured to configure a short processing time. A physical downlink control channel (PDCCH) receiver is configured to receive, in a subframe n, a PDCCH. A channel state information (CSI) request field of the PDCCH is set to trigger an aperiodic CSI report. A physical uplink shared channel (PUSCH) transmitter is configured to transmit, in the subframe n+k, a PUSCH corresponding to the PDCCH. The aperiodic CSI report is performed on the PUSCH. In a case that the PUSCH is not a PUSCH based on the short processing time, a CSI reference resource for the aperiodic CSI report is the subframe n. In a case that the PUSCH is a PUSCH based on the short processing time, the CSI reference resource is the subframe n+k−n ref . The n ref  is larger than the k. 
     An evolved node B (eNB) is also described. A higher-layer processor is configured to configure, for a UE, a short processing time. A PDCCH transmitter is configured to transmit, in a subframe n, a PDCCH. A CSI request field of the PDCCH is set to trigger an aperiodic CSI report. A PUSCH receiver is configured to receive, in the subframe n+k, a PUSCH corresponding to the PDCCH. The aperiodic CSI report is performed on the PUSCH. In a case that the PUSCH is not a PUSCH based on the short processing time, a CSI reference resource for the aperiodic CSI report is the subframe n. In a case that the PUSCH is a PUSCH based on the short processing time, the CSI reference resource is the subframe n+k−n ref . The n ref  is larger than the k. 
     A method for a UE is also described. The method includes configuring a short processing time. The method also includes receiving, in a subframe n, a PDCCH of which a CSI request field is set to trigger an aperiodic CSI report. The method further includes transmitting, in the subframe n+k, a PUSCH corresponding to the PDCCH, the aperiodic CSI report being performed on the PUSCH. In a case that the PUSCH is not a PUSCH based on the short processing time, a CSI reference resource for the aperiodic CSI report is the subframe n. In a case that the PUSCH is a PUSCH based on the short processing time, the CSI reference resource is the subframe n+k−n ref . The n ref  is larger than the k. 
     A method for an eNB is also described. The method includes configuring, for a UE, a short processing time. The method also includes transmitting, in a subframe n, a PDCCH of which a CSI request field is set to trigger an aperiodic CSI report. The method further includes receiving, in the subframe n+k, a physical downlink shared channel (PDSCH) corresponding to the PDCCH, the aperiodic CSI report being performed on the PUSCH. In a case that the PUSCH is not a PUSCH based on the short processing time, a CSI reference resource for the aperiodic CSI report is the subframe n. In a case that the PUSCH is a PUSCH based on the short processing time, the CSI reference resource is the subframe n+k−n ref . The n ref  is larger than the k. 
     The 3rd Generation Partnership Project, also referred to as “3GPP,” is a collaboration agreement that aims to define globally applicable technical specifications and technical reports for third and fourth generation wireless communication systems. The 3GPP may define specifications for next generation mobile networks, systems and devices. 
     3GPP Long Term Evolution (LTE) is the name given to a project to improve the Universal Mobile Telecommunications System (UMTS) mobile phone or device standard to cope with future requirements. In one aspect, UMTS has been modified to provide support and specification for the Evolved Universal Terrestrial Radio Access (E-UTRA) and Evolved Universal Terrestrial Radio Access Network (E-UTRAN). 
     At least some aspects of the systems and methods disclosed herein may be described in relation to the 3GPP LTE, LTE-Advanced (LTE-A) and other standards (e.g., 3GPP Releases 8, 9, 10, 11 and/or 12). However, the scope of the present disclosure should not be limited in this regard. At least some aspects of the systems and methods disclosed herein may be utilized in other types of wireless communication systems. 
     A wireless communication device may be an electronic device used to communicate voice and/or data to a base station, which in turn may communicate with a network of devices (e.g., public switched telephone network (PSTN), the Internet, etc.). In describing systems and methods herein, a wireless communication device may alternatively be referred to as a mobile station, a UE, an access terminal, a subscriber station, a mobile terminal, a remote station, a user terminal, a terminal, a subscriber unit, a mobile device, etc. Examples of wireless communication devices include cellular phones, smart phones, personal digital assistants (PDAs), laptop computers, netbooks, e-readers, wireless modems, etc. In 3GPP specifications, a wireless communication device is typically referred to as a UE. However, as the scope of the present disclosure should not be limited to the 3GPP standards, the terms “UE” and “wireless communication device” may be used interchangeably herein to mean the more general term “wireless communication device.” A UE may also be more generally referred to as a terminal device. 
     In 3GPP specifications, a base station is typically referred to as a Node B, an evolved Node B (eNB), a home enhanced or evolved Node B (HeNB) or some other similar terminology. As the scope of the disclosure should not be limited to 3GPP standards, the terms “base station,” “Node B,” “eNB,” and “HeNB” may be used interchangeably herein to mean the more general term “base station.” Furthermore, the term “base station” may be used to denote an access point. An access point may be an electronic device that provides access to a network (e.g., Local Area Network (LAN), the Internet, etc.) for wireless communication devices. The term “communication device” may be used to denote both a wireless communication device and/or a base station. An eNB may also be more generally referred to as a base station device. 
     It should be noted that as used herein, a “cell” may be any communication channel that is specified by standardization or regulatory bodies to be used for International Mobile Telecommunications-Advanced (IMT-Advanced) and all of it or a subset of it may be adopted by 3GPP as licensed bands (e.g., frequency bands) to be used for communication between an eNB and a UE. It should also be noted that in E-UTRA and E-UTRAN overall description, as used herein, a “cell” may be defined as “combination of downlink and optionally uplink resources.” The linking between the carrier frequency of the downlink resources and the carrier frequency of the uplink resources may be indicated in the system information transmitted on the downlink resources. 
     “Configured cells” are those cells of which the UE is aware and is allowed by an eNB to transmit or receive information. “Configured cell(s)” may be serving cell(s). The UE may receive system information and perform the required measurements on all configured cells. “Configured cell(s)” for a radio connection may include a primary cell and/or no, one, or more secondary cell(s). “Activated cells” are those configured cells on which the UE is transmitting and receiving. That is, activated cells are those cells for which the UE monitors the physical downlink control channel (PDCCH) and in the case of a downlink transmission, those cells for which the UE decodes a physical downlink shared channel (PDSCH). “Deactivated cells” are those configured cells that the UE is not monitoring the transmission PDCCH. It should be noted that a “cell” may be described in terms of differing dimensions. For example, a “cell” may have temporal, spatial (e.g., geographical) and frequency characteristics. 
     The systems and methods disclosed may involve carrier aggregation (CA). Carrier aggregation refers to the concurrent utilization of more than one carrier. In carrier aggregation, more than one cell may be aggregated to a UE. In one example, carrier aggregation may be used to increase the effective bandwidth available to a UE. The same time division duplexing (TDD) uplink-downlink (UL/DL) configuration has to be used for TDD CA in Release-10, and for intra-band CA in Release-11. In Release-11, interband TDD CA with different TDD UL/DL configurations is supported. The inter-band TDD CA with different TDD UL/DL configurations may provide the flexibility of a TDD network in CA deployment. Furthermore, enhanced interference management with traffic adaptation (eIMTA) (also referred to as dynamic UL/DL reconfiguration) may allow flexible TDD UL/DL reconfiguration based on the network traffic load. 
     It should be noted that the term “concurrent” and variations thereof as used herein may denote that two or more events may overlap each other in time and/or may occur near in time to each other. Additionally, “concurrent” and variations thereof may or may not mean that two or more events occur at precisely the same time. 
     Packet data latency is a performance metric of a communication system. There is a requirement to reduce the latency from the view point of the perceived responsiveness of the system for new features (e.g., real-time communication for robotics applications) as well as the more efficient transactions of the current HTTP/TCP-based packets. In addition, it is said that the Tactile Internet, which will have significant impacts on future business, market and human lives, needs extremely reduced latency signals. The Tactile Internet could be provided through the same band as the current cellular communication, a different band (e.g., a higher frequency band such as a millimeter wave) or both of them. 
     A promising candidate for realizing the latency reduction is shortened Round Trip Time (RTT). However, coexistence of normal and shortened RTTs has not been defined. 
     The systems and methods described herein provide a sufficient processing time for CSI measurements when shortened RTT is configured. Typical configuration may be as follows. In a case where aperiodic CSI is triggered by a PDCCH that schedules a PUSCH with normal RTT, a CSI reference resource for the aperiodic CSI report may be the same subframe as the subframe where the PDCCH is transmitted. In case where aperiodic CSI is triggered by a PDCCH that schedules a PUSCH with shortened RTT, a CSI reference resource for the aperiodic CSI report may be allowed to be a valid subframe prior to the subframe where the PDCCH is transmitted. 
     Various examples of the systems and methods disclosed herein are now described with reference to the Figures, where like reference numbers may indicate functionally similar elements. The systems and methods as generally described and illustrated in the Figures herein could be arranged and designed in a wide variety of different implementations. Thus, the following more detailed description of several implementations, as represented in the Figures, is not intended to limit scope, as claimed, but is merely representative of the systems and methods. 
       FIG. 1  is a block diagram illustrating one implementation of one or more eNBs  160  and one or more UEs  102  in which systems and methods for low latency radio communications may be implemented. The one or more UEs  102  communicate with one or more eNBs  160  using one or more antennas  122   a - n.  For example, a UE  102  transmits electromagnetic signals to the eNB  160  and receives electromagnetic signals from the eNB  160  using the one or more antennas  122   a - n.  The eNB  160  communicates with the UE  102  using one or more antennas  180   a - n.    
     The UE  102  and the eNB  160  may use one or more channels  119 ,  121  to communicate with each other. For example, a UE  102  may transmit information or data to the eNB  160  using one or more uplink channels  121 . Examples of uplink channels  121  include a physical uplink control channel (PUCCH) and a PUSCH, etc. The one or more eNBs  160  may also transmit information or data to the one or more UEs  102  using one or more downlink channels  119 , for instance. Examples of downlink channels  119  include a PDCCH, a PDSCH, etc. Other kinds of channels may be used. 
     Each of the one or more UEs  102  may include one or more transceivers  118 , one or more demodulators  114 , one or more decoders  108 , one or more encoders  150 , one or more modulators  154 , a data buffer  104  and a UE operations module  124 . For example, one or more reception and/or transmission paths may be implemented in the UE  102 . For convenience, only a single transceiver  118 , decoder  108 , demodulator  114 , encoder  150  and modulator  154  are illustrated in the UE  102 , though multiple parallel elements (e.g., transceivers  118 , decoders  108 , demodulators  114 , encoders  150  and modulators  154 ) may be implemented. 
     The transceiver  118  may include one or more receivers  120  and one or more transmitters  158 . The one or more receivers  120  may receive signals from the eNB  160  using one or more antennas  122   a - n.  For example, the receiver  120  may receive and downconvert signals to produce one or more received signals  116 . The one or more received signals  116  may be provided to a demodulator  114 . The one or more transmitters  158  may transmit signals to the eNB  160  using one or more antennas  122   a - n.  For example, the one or more transmitters  158  may upconvert and transmit one or more modulated signals  156 . 
     The demodulator  114  may demodulate the one or more received signals  116  to produce one or more demodulated signals  112 . The one or more demodulated signals  112  may be provided to the decoder  108 . The UE  102  may use the decoder  108  to decode signals. The decoder  108  may produce decoded signals  110 , which may include a UE-decoded signal  106  (also referred to as a first UE-decoded signal  106 ). For example, the first UE-decoded signal  106  may comprise received payload data, which may be stored in a data buffer  104 . Another signal included in the decoded signals  110  (also referred to as a second UE-decoded signal  110 ) may comprise overhead data and/or control data. For example, the second UE-decoded signal  110  may provide data that may be used by the UE operations module  124  to perform one or more operations. 
     In general, the UE operations module  124  may enable the UE  102  to communicate with the one or more eNBs  160 . The UE operations module  124  may include one or more of a UE reduced latency module  126 . 
     Downlink and uplink transmissions may be organized into radio frames with a 10 millisecond (ms) duration. For a frame structure Type 1 (e.g., frequency division duplexing (FDD)), each 10 ms radio frame is divided into ten equally sized sub-frames. Each sub-frame includes two equally sized slots. For a frame structure Type 2 (e.g., TDD), each 10 ms radio frame includes two half-frames of 5 ms each. Each half-frame includes eight slots of length 0.5 ms and three special fields: DwPTS, guard period (GP) and UpPTS. The length of DwPTS and UpPTS is configurable subject to the total length of DwPTS, GP and UpPTS being equal to 1 ms. Additional details about frame structure are discussed in connection with  FIG. 5 . 
     Both 5 ms and 10 ms switch-point periodicity are supported. Subframe 1 in all configurations and subframe 6 in a configuration with 5 ms switch-point periodicity include DwPTS, GP and UpPTS. Subframe 6 in a configuration with 10 ms switch-point periodicity includes DwPTS only. All other subframes include two equally sized slots. 
     In LTE license access, subframes are classified into 2 types of subframes. One is the normal subframe that contains only either one of DL transmission and UL transmission. LTE license access with FDD has only the normal subframe. The other is the special subframe that contains three fields DwPTS, GP and UpPTS. DwPTS and UpPTS are durations reserved for DL transmission and UL transmission, respectively. 
     LTE license access with TDD can have the special subframe as well as the normal subframe. The lengths of DwPTS, GP and UpPTS can be configured by using a special subframe configuration. Any one of the following ten configurations may be set as a special subframe configuration. 
     1) Special subframe configuration 0: DwPTS includes 3 Orthogonal Frequency Division Multiplexing (OFDM) symbols. UpPTS includes 1 single carrier frequency-division multiple access (SC-FDMA) symbol. 
     2) Special subframe configuration 1: DwPTS includes 9 OFDM symbols for normal cyclic prefix (CP) and 8 OFDM symbols for extended CP. UpPTS includes 1 SC-FDMA symbol. 
     3) Special subframe configuration 2: DwPTS includes 10 OFDM symbols for normal CP and 9 OFDM symbols for extended CP. UpPTS includes 1 SC-FDMA symbol. 
     4) Special subframe configuration 3: DwPTS includes 11 OFDM symbols for normal CP and 10 OFDM symbols for extended CP. UpPTS includes 1 SC-FDMA symbol. 
     5) Special subframe configuration 4: DwPTS includes 12 OFDM symbols for normal CP and 3 OFDM symbols for extended CP. UpPTS includes 1 SC-FDMA symbol for normal CP and 2 SC-FDMA symbol for extended CP. 
     6) Special subframe configuration 5: DwPTS includes 3 OFDM symbols for normal CP and 8 OFDM symbols for extended CP. UpPTS includes 2 SC-FDMA symbols. 
     7) Special subframe configuration 6: DwPTS includes 9 OFDM symbols. UpPTS includes 2 SC-FDMA symbols. 
     8) Special subframe configuration 7: DwPTS includes 10 OFDM symbols for normal CP and 5 OFDM symbols for extended CP. UpPTS includes 2 SC-FDMA symbols. 
     9) Special subframe configuration 8: DwPTS includes 11 OFDM symbols. UpPTS includes 2 SC-FDMA symbols. Special subframe configuration 8 can be configured only for normal CP 
     10) Special subframe configuration 9: DwPTS includes 6 OFDM symbols. UpPTS includes 2 SC-FDMA symbols. Special subframe configuration 9 can be configured only for normal CP. 
     Frame structure Type 3 may be applicable to Licensed-Assisted Access (LAA) secondary cell operation with normal cyclic prefix only. The 10 subframes within a radio frame are available for downlink transmissions. Downlink transmissions occupy one or more consecutive subframes, starting anywhere within a subframe and ending with the last subframe either fully occupied or one of the DwPTS durations and structures. 
     For a UE  102  not capable of UL LAA, if the UE  102  is configured with a LAA SCell, the UE  102  may apply physical layer procedures assuming frame structure type 1 for the LAA SCell unless stated otherwise. 
     In the downlink, the OFDM access scheme may be employed. In the downlink, PDCCH, enhanced physical downlink control channel (EPDCCH), PDSCH and the like may be transmitted. A downlink radio frame may include multiple pairs of downlink resource blocks (RBs). The downlink RB pair is a unit for assigning downlink radio resources, defined by a predetermined bandwidth (RB bandwidth) and a time slot. Two slots (i.e., slot 0  and slot 1 ) equal one subframe. The downlink RB pair includes two downlink RBs that are continuous in the time domain. 
     The downlink RB includes twelve sub-carriers in frequency domain and seven (for normal CP) or six (for extended CP) OFDM symbols in time domain. A region defined by one sub-carrier in frequency domain and one OFDM symbol in time domain is referred to as a resource element (RE) and is uniquely identified by the index pair (k, l) in a slot, where k and l are indices in the frequency and time domains, respectively. While downlink subframes in one component carrier (CC) are discussed herein, downlink subframes are defined for each CC and downlink subframes are substantially in synchronization with each other among CCs. An example of a resource grid is discussed in connection with  FIG. 6 . 
     In the uplink, a Single-Carrier Frequency Division Multiple Access (SC-FDMA) access scheme may be employed. In the uplink, PUCCH, PDSCH, Physical Random Access Channel (PRACH) and the like may be transmitted. An uplink radio frame may include multiple pairs of uplink resource blocks. The uplink RB pair is a unit for assigning uplink radio resources, defined by a predetermined bandwidth (RB bandwidth) and a time slot. Two slots (i.e., slot 0  and slot 1 ) equal one subframe. The uplink RB pair includes two uplink RBs that are continuous in the time domain. 
     The uplink RB may include twelve sub-carriers in frequency domain and seven (for normal CP) or six (for extended CP) SC-FDMA symbols in time domain. A region defined by one sub-carrier in the frequency domain and one SC-FDMA symbol in the time domain is referred to as a RE and is uniquely identified by the index pair (k,l) in a slot, where k and l are indices in the frequency and time domains respectively. While uplink subframes in one component carrier (CC) are discussed herein, uplink subframes are defined for each CC. An example of a resource grid in the uplink is discussed in connection with  FIG. 7 . 
     In Carrier Aggregation (CA), two or more CCs may be aggregated to support wider transmission bandwidths (e.g., up to 100 MHz, beyond 100 MHz). A UE  102  may simultaneously receive or transmit on one or multiple CCs. Serving cells can be classified into a primary cell (PCell) and a secondary cell (SCell). 
     The primary cell may be the cell, operating on the primary frequency, in which the UE  102  either performs the initial connection establishment procedure or initiates the connection re-establishment procedure, or the cell indicated as the primary cell in the handover procedure. The secondary cell may be a cell, operating on a secondary frequency, which may be configured once a Radio Resource Control (RRC) connection is established and which may be used to provide additional radio resources. 
     In the downlink, the carrier corresponding to the PCell is the downlink primary component carrier (DL PCC) while in the uplink it is the uplink primary component carrier (UL PCC). Similarly, in the downlink, the carrier corresponding to the SCell is the downlink secondary component carrier (DL SCC) while in the uplink it is the uplink secondary component carrier (UL SCC). The UE  102  may apply a system information acquisition (i.e., acquisition of broadcast system information) and change monitoring procedures for the PCell. For an SCell, E-UTRAN may provide, via dedicated signaling, all system information relevant for operation in an RRC_CONNECTED message when adding the SCell. 
     In Dual Connectivity (DC), each of two or more serving cells may belong to either one of a master cell group (MCG) or a secondary cell group (SCG). The MCG is associated with a master eNB (MeNB) while the SCG is associated with a secondary eNB (SeNB). 
     DC operation may be configured to utilize radio resources provided by two distinct schedulers, located in the MeNB and SeNB. In the case of DC, the UE  102  may be configured with two Medium Access Control (MAC) entities: one MAC entity for MeNB and one MAC entity for SeNB. 
     When a UE  102  is configured with CA in the MCG, CA principles may generally apply to the MCG. For the SCG, at least one cell in the SCG has a configured UL CC and one of them, named the primary secondary cell (PSCell), is configured with physical uplink control channel (PUCCH) resources. Unlike the CA for which a UE  102  should cope with a delay spread of up to 30.26 μs among the component carriers, two operations are defined for the DC: synchronous and asynchronous DC. In synchronous DC operation, the UE  102  can cope with a maximum reception timing difference up to at least 33 μs between cell groups (CGs). In asynchronous DC operation, the UE  102  can cope with a maximum reception timing difference up to 500 μs between CGs. 
     Even in the case that DC is not configured, one or more PUCCH cell group(s) can be configured. A PUCCH cell group having a PCell may be referred to as a MCG or master PUCCH cell group (MPCG). The other cell group(s) may be referred to as a SCG or secondary PUCCH cell group (SPCG). Each SCG (or SPCG) may include a PSCell, on which a PUCCH transmission(s) for the SCG (or SPCG) can be performed. 
     A downlink physical channel may correspond to a set of resource elements carrying information originating from higher layers. The following downlink physical channels may be defined. A physical downlink shared channel (PDSCH) may carry a transport block provided by a higher layer. The transport block may contain user data, higher layer control messages, physical layer system information. The scheduling assignment of PDSCH in a given subframe may normally be carried by PDCCH or EPDCCH in the same subframe. 
     A physical broadcast channel (PBCH) may carry a master information block, which is required for an initial access. 
     A physical multicast channel (PMCH) may carry Multimedia Broadcast Multicast Services (MBMS) related data and control information. 
     A physical control format indicator channel (PCFICH) may carry a control format indicator (CFI) specifying the number of OFDM symbols on which PDCCHs are mapped. 
     A physical downlink control channel (PDCCH) may carry a scheduling assignment (also referred to as a DL grant) or an UL grant. The PDCCH may be transmitted via the same antenna port (e.g., cell-specific reference signal (CRS) port) as the PBCH. 
     A physical hybrid ARQ indicator channel (PHICH) may carry UL-associated hybrid automatic repeat request-acknowledgement (HARQ-ACK) information. 
     An enhanced physical downlink control channel (EPDCCH) may carry a scheduling assignment or an UL grant. The EPDCCH may be transmitted via a different antenna port (e.g., demodulation reference signal (DM-RS) port) from the PBCH and PDCCH. Possible REs on which EPDCCHs are mapped may be different from those for PDCCH, though they may partially overlap. 
     A downlink physical signal may correspond to a set of resource elements used by the physical layer but may not carry information originating from higher layers. 
     A cell-specific reference signal (CRS) may be assumed to be transmitted in all downlink subframes and DwPTS. For a normal subframe with normal CP, a CRS may be mapped on REs that are located in the 1st, 2nd, and 5th OFDM symbols in each slot. A CRS may be used for demodulation of the PDSCH, CSI measurement and Radio Resource Management (RRM) measurement. 
     A CSI reference signal (CSI-RS) may be transmitted in the subframes that are configured by higher layer signaling. The REs on which a CSI-RS is mapped are also configured by higher layer signaling. A CSI-RS may be further classified into non zero power (NZP) CSI-RS and ZP (zero power) CSI-RS. A part of a ZP CSI-RS resources may be configured as a CSI-interference measurement (CSI-IM) resource, which may be used for interference measurement. 
     A UE-specific reference signal (RS) (UE-RS) may be assumed to be transmitted in Physical Resource Block (PRB) pairs that are allocated for the PDSCH intended to the UE  102 . UE-RS may be used for demodulation of the associated PDSCH. 
     A Demodulation RS (DM-RS) may be assumed to be transmitted in PRB pairs that are allocated for EPDCCH transmission. DM-RS may be used for demodulation of the associated EPDCCH. 
     Primary/secondary synchronization signals may be transmitted to facilitate the UE&#39;s  102  cell search, which is the procedure by which the UE  102  acquires time and frequency synchronization with a cell and detects the physical layer Cell ID of that cell. E-UTRA cell search supports a scalable overall transmission bandwidth corresponding to 6 resource blocks and upwards. 
     A discovery signal may include CRS, primary/secondary synchronization signals NZP-CSI-RS (if configured). The UE  102  may assume a discovery signal occasion once every discovery reference signal (DRS) measurement timing configuration (DMTC)-Periodicity. The eNB  160  using cell on/off may adaptively turn the downlink transmission of a cell on and off. A cell whose downlink transmission is turned off may be configured as a deactivated SCell for a UE  102 . A cell performing on/off may transmit only periodic discovery signals and UEs  102  may be configured to measure the discovery signals for RRM. A UE  102  may perform RRM measurement and may discover a cell or transmission point of a cell based on discovery signals when the UE  102  is configured with discovery-signal-based measurements. 
     Uplink physical channels and uplink physical signals are also described herein. An uplink physical channel may correspond to a set of resource elements carrying information originating from higher layers. The following uplink physical channels may be defined. A Physical Uplink Shared Channel (PUSCH) may carry a transport block provided by a higher layer. The transport block may contain user data and/or higher layer control messages. An uplink grant of PUSCH in a given subframe may normally be carried by PDCCH or EPDCCH several subframes before the given subframe. A Physical Uplink Control Channel (PUCCH) may carry DL-associated HARQ-ACK information, a scheduling request, and/or CSI. A PRACH may carry a random access preamble. 
     An uplink physical signal may correspond to a set of resource elements used by the physical layer but may not carry information originating from higher layers. Reference signals (RS) are described herein. A PUSCH DM-RS (Demodulation RS) may be assumed to be transmitted in PRB pairs that are allocated for the PUSCH transmitted by the UE  102 . PUSCH DM-RS may be used for demodulation of the associated PUSCH. PUSCH DM-RS may be mapped on REs that are located in the 4th SC-FDMA symbol in each slot. 
     PUCCH DM-RS (Demodulation RS) may be assumed to be transmitted in PRB pairs that are allocated for the PUCCH transmitted by the UE  102 . PUCCH DM-RS may be used for demodulation of the associated PUCCH. For PUCCH format 1, 1a and 1b, PUCCH DM-RS may be mapped on REs which are located in the 3rd, 4th and 5th SC-FDMA symbols in each slot. For PUCCH format 2, 2a, 2b and 3, PUCCH DM-RS may be mapped on REs that are located in the 2nd and 6th SC-FDMA symbols in each slot. For PUCCH format 4 and 5, PUCCH DM-RS may be mapped on REs that are located in the 4th SC-FDMA symbol in each slot. 
     A sounding RS (SRS) may be transmitted in the last SC-FDMA symbol in uplink subframe or in 1 of 2 SC-FDMA symbol(s) in UpPTS. 
     A UE sounding procedure is also described herein. A UE  102  may transmit SRS on serving cell SRS resources based on two trigger types: trigger type 0 (higher layer signaling); or trigger type 1 (downlink control information (DCI) formats 0/4/1A for FDD and TDD and DCI formats 2B/2C/2D for TDD). In case both trigger type 0 and trigger type 1 SRS transmissions would occur in the same subframe in the same serving cell, the UE  102  may only transmit the trigger type 1 SRS transmission. 
     A UE  102  may be configured with SRS parameters for trigger type 0 and trigger type 1 on each serving cell. For trigger type 0, only a single set of SRS parameters may be used. For trigger type 1 and DCI format 4, three sets of SRS parameters (e.g., srs-ConfigApDCI-Format4) may be configured by higher layer signaling. The 2-bit SRS request field in DCI format 4 indicates the SRS parameter set given in Table 1. For trigger type 1 and DCI format 0, a single set of SRS parameters (e.g., srs-ConfigApDCI-Format0) may be configured by higher layer signaling. For trigger type 1 and DCI formats 1A/2B/2C/2D, a single common set of SRS parameters (e.g., srs-ConfigApDCI-Format1a 2b2c) may be configured by higher layer signaling. The SRS request field may be 1 bit for DCI formats 0/1A/2B/2C/2D, with a type 1 SRS triggered if the value of the SRS request field is set to “1”. 
     A 1-bit SRS request field may be included in DCI formats 0/1A for frame structure type 1 and 0/1A/2B/2C/2D for frame structure type 2 if the UE  102  is configured with SRS parameters for DCI formats 0/1A/2B/2C/2D by higher-layer signaling. Table 1 provides an SRS request value for trigger type 1 in DCI format 4. 
     
       
         
           
               
               
             
               
                 TABLE 1 
               
               
                   
               
               
                 Value of SRS 
                   
               
               
                 request field 
                 Description 
               
               
                   
               
             
            
               
                 ‘00’ 
                 No type 1 SRS trigger 
               
               
                 ‘01’ 
                 The 1 st  SRS parameter set configured by higher layers 
               
               
                 ‘10’ 
                 The 2 nd  SRS parameter set configured by higher layers 
               
               
                 ‘11’ 
                 The 3 rd  SRS parameter set configured by higher layers 
               
               
                   
               
            
           
         
       
     
     Trigger type 0 SRS configuration of a UE  102  in a serving cell for SRS periodicity (T SRS ) and SRS subframe offset (T offset ) may be derived using higher layer parameter  1   SRS . The periodicity T SRS  of the SRS transmission is serving cell specific and may be selected from the set {2, 5, 10, 20, 40, 80, 160, 320} ms or subframes. For the SRS periodicity T SRS  of 2 ms in TDD serving cell, two SRS resources may be configured in a half frame containing UL subframe(s) of the given serving cell. 
     Trigger type 1 SRS configuration of a UE  102  in a serving cell for SRS periodicity (T SRS,1 ) and SRS subframe offset (T offset,1 ) may be derived using higher layer parameter  1   SRS . The periodicity T SRS,1  of the SRS transmission is serving cell specific and may be selected from the set {2, 5, 10} ms or subframes. For the SRS periodicity T SRS,1  of 2 ms in TDD serving cell, two SRS resources may be configured in a half frame containing UL subframe(s) of the given serving cell. 
     In Rel-12, there are ten transmission modes. These transmission modes may be configurable for an LAA SCell. These transmission modes are illustrated in Table 2. 
     
       
         
           
               
               
               
             
               
                 TABLE 2 
               
               
                   
               
               
                 Transmission 
                   
                   
               
               
                 mode 
                 DCI format 
                 Transmission scheme 
               
               
                   
               
             
            
               
                 Mode 1 
                 DCI format 1A 
                 Single antenna port 
               
               
                   
                 DCI format 1 
                 Single antenna port 
               
               
                 Mode 2 
                 DCI format 1A 
                 Transmit diversity 
               
               
                   
                 DCI format 1 
                 Transmit diversity 
               
               
                 Mode 3 
                 DCI format 1A 
                 Transmit diversity 
               
               
                   
                 DCI format 2A 
                 Large delay Cyclic Delay Diversity (CDD) or 
               
               
                   
                   
                 Transmit diversity 
               
               
                 Mode 4 
                 DCI format 1A 
                 Transmit diversity 
               
               
                   
                 DCI format 2 
                 Closed-loop spatial multiplexing or Transmit 
               
               
                   
                   
                 diversity 
               
               
                 Mode 5 
                 DCI format 1A 
                 Transmit diversity 
               
               
                   
                 DCI format 1D 
                 Multi-user Multiple-Input Multiple-Output 
               
               
                   
                   
                 (MIMO) 
               
               
                 Mode 6 
                 DCI format 1A 
                 Transmit diversity 
               
               
                   
                 DCI format 1B 
                 Closed-loop spatial multiplexing using a single 
               
               
                   
                   
                 transmission layer 
               
               
                 Mode 7 
                 DCI format 1A 
                 Single-antenna port (for a single CRS port), 
               
               
                   
                   
                 transmit diversity (otherwise) 
               
               
                   
                 DCI format 1 
                 Single-antenna port 
               
               
                 Mode 8 
                 DCI format 1A 
                 Single-antenna port (for a single CRS port), 
               
               
                   
                   
                 transmit diversity (otherwise) 
               
               
                   
                 DCI format 2B 
                 Dual layer transmission or single-antenna port 
               
               
                 Mode 9 
                 DCI format 1A 
                 Single-antenna port (for a single CRS port or 
               
               
                   
                   
                 Multimedia Broadcast Single Frequency Network 
               
               
                   
                   
                 (MBSFN) subframe), transmit diversity 
               
               
                   
                   
                 (otherwise) 
               
               
                   
                 DCI format 2C 
                 Up to 8 layer transmission or single-antenna port 
               
               
                 Mode 10 
                 DCI format 1A 
                 Single-antenna port (for a single CRS port or 
               
               
                   
                   
                 MBSFN subframe), transmit diversity (otherwise) 
               
               
                   
                 DCI format 2D 
                 Up to 8 layer transmission or single-antenna port 
               
               
                   
               
            
           
         
       
     
     DCI format 1, 1A, 1B, 1C, 1D, 2, 2A, 2B, 2C, and 2D may be used for DL assignment (also referred to as DL grant). DCI format 0, and 4 may be used for UL grant. The DCI formats are illustrated in Table 3. 
     
       
         
           
               
               
             
               
                 TABLE 3 
               
               
                   
               
               
                 DCI format 
                 Use 
               
               
                   
               
             
            
               
                 DCI format 0 
                 scheduling of PUSCH in one UL cell 
               
               
                 DCI format 1 
                 scheduling of one PDSCH codeword in one cell 
               
               
                 DCI format 1A 
                 compact scheduling of one PDSCH codeword in one cell and 
               
               
                   
                 random access procedure initiated by a PDCCH order 
               
               
                 DCI format 1B 
                 compact scheduling of one PDSCH codeword in one cell with 
               
               
                   
                 precoding information 
               
               
                 DCI format 1C 
                 very compact scheduling of one PDSCH codeword, notifying 
               
               
                   
                 Multicast Control Channel (MCCH) change, reconfiguring TDD, 
               
               
                   
                 and LAA common information 
               
               
                 DCI format 1D 
                 compact scheduling of one PDSCH codeword in one cell with 
               
               
                   
                 precoding and power offset information 
               
               
                 DCI format 1A 
                 Transmit diversity 
               
               
                 DCI format 2 
                 scheduling of up to two PDSCH codewords in one cell with 
               
               
                   
                 precoding information 
               
               
                 DCI format 2A 
                 scheduling of up to two PDSCH codewords in one cell 
               
               
                 DCI format 2B 
                 scheduling of up to two PDSCH codewords in one cell with 
               
               
                   
                 scrambling identity information 
               
               
                 DCI format 2C 
                 scheduling of up to two PDSCH codewords in one cell with antenna 
               
               
                   
                 port, scrambling identity and number of layers information 
               
               
                 DCI format 2D 
                 scheduling of up to two PDSCH codewords in one cell with antenna 
               
               
                   
                 port, scrambling identity and number of layers information and 
               
               
                   
                 PDSCH RE Mapping and Quasi-Co-Location Indicator (PQI) 
               
               
                   
                 information 
               
               
                 DCI format 3 
                 transmission of transmitter power control (TPC) commands for 
               
               
                   
                 PUCCH and PUSCH with 2-bit power adjustments 
               
               
                 DCI format 3A 
                 transmission of TPC commands for PUCCH and PUSCH with 
               
               
                   
                 single bit power adjustments 
               
               
                 DCI format 4 
                 of PUSCH in one UL cell with multi-antenna port transmission 
               
               
                   
                 mode 
               
               
                 DCI format 5 
                 scheduling of Physical Sidelink Broadcast Channel (PSCCH), and 
               
               
                   
                 also contains several Sidelink Control Information (SCI) format 0 
               
               
                   
                 fields used for the scheduling of Physical Sidelink Shared Channel 
               
               
                   
                 (PSSCH) 
               
               
                   
               
            
           
         
       
     
     DCI format 1, 1A, 1B, 1C, 1D may include the bit fields provided in Table 4, where N DL   RB  is a downlink system band width of the serving cell, which is expressed in multiples of PRB (physical resource block) bandwidth. 
     
       
         
           
               
               
               
               
               
               
             
               
                   
                 TABLE 4 
               
               
                   
                   
               
               
                   
                 DCI F 1 
                 DCI F 1A 
                 DCI F 1B 
                 DCI F 1C 
                 DCI F 1D 
               
               
                   
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
               
               
            
               
                 Carrier Indicator 
                 0 or 3 
                 0 or 3 
                 0 or 3 
                 N/A 
                 0 or 3 
               
               
                 Field (CIF) 
               
               
                 Flag for format0/1A 
                 N/A 
                 1 
                 N/A 
                 N/A 
                 N/A 
               
               
                 differentiation 
               
               
                 Localized/Distributed 
                 N/A 
                 1 
                 1 
                 N/A 
                 1 
               
               
                 Virtual Resource 
               
               
                 Block (VRB) 
               
               
                 assignment flag 
               
               
                 Resource allocation 
                 1 
                 N/A 
                 N/A 
                 N/A 
                 N/A 
               
               
                 header 
               
               
                 Gap value 
                 N/A 
                 N/A 
                 N/A 
                 0 
                 N/A 
               
               
                   
                   
                   
                   
                 (N DL RB &lt; 50) 
               
               
                   
                   
                   
                   
                 or 1 
               
               
                   
                   
                   
                   
                 (otherwise) 
               
               
                 Resource block 
                 * 
                 ** 
                 ** 
                 *** 
                 ** 
               
               
                 assignment 
               
               
                 Modulation and 
                 5 
                 5 
                 5 
                 5 
                 5 
               
               
                 coding scheme 
               
               
                 HARQ process 
                 3 (FDD 
                 3 (FDD 
                 3 (FDD 
                 N/A 
                 3 (FDD 
               
               
                 number 
                 PCell) or 4 
                 PCell) or 4 
                 PCell) or 4 
                   
                 PCell) or 4 
               
               
                   
                 (TDD 
                 (TDD 
                 (TDD 
                   
                 (TDD 
               
               
                   
                 PCell) 
                 PCell) 
                 PCell) 
                   
                 PCell) 
               
               
                 New data indicator 
                 1 
                 1 
                 1 
                 N/A 
                 1 
               
               
                 Redundancy version 
                 2 
                 2 
                 2 
                 N/A 
                 2 
               
               
                 TPC command for 
                 2 
                 2 
                 2 
                 N/A 
                 2 
               
               
                 PUCCH 
               
               
                 Downlink 
                 0 (FDD 
                 0 (FDD 
                 0 (FDD 
                 N/A 
                 0 (FDD 
               
               
                 Assignment Index 
                 PCell) or 2 
                 PCell) or 2 
                 PCell) or 2 
                   
                 PCell) or 2 
               
               
                   
                 (otherwise) 
                 (otherwise) 
                 (otherwise) 
                   
                 (otherwise) 
               
               
                 SRS request 
                 N/A 
                 0 or 1 
                 N/A 
                 N/A 
                 N/A 
               
               
                 Downlink power 
                 N/A 
                 N/A 
                 N/A 
                 N/A 
                 1 
               
               
                 offset 
               
               
                 Transmitted 
                 N/A 
                 N/A 
                 2 (2 CRS 
                 N/A 
                 2 (2 CRS 
               
               
                 Precoding Matrix 
                   
                   
                 ports) or 4 
                   
                 ports) or 4 
               
               
                 Indicator (TPMI) 
                   
                   
                 (4 CRS 
                   
                 (4 CRS 
               
               
                 information for 
                   
                   
                 ports) 
                   
                 ports) 
               
               
                 precoding 
               
               
                 HARQ-ACK 
                 2 
                 2 
                 2 
                 N/A 
                 2 
               
               
                 resource offset 
                 (EPDCCH) 
                 (EPDCCH) 
                 (EPDCCH) 
                   
                 (EPDCCH) 
               
               
                   
                 or 0 
                 or 0 
                 or 0 
                   
                 or 0 
               
               
                   
                 (PDCCH) 
                 (PDCCH) 
                 (PDCCH) 
                   
                 (PDCCH) 
               
               
                   
               
            
           
         
       
     
     It should be noted that * is ceil(N DL   RB /P) bits, where P is determined from Table 5; ** is ceil(log 2 (N DL   RB (N DL   RB +1)/2)) bits; and *** is ceil(log 2 (floor(N DL   VRB,gap1 /N step   RB )(floor (N DL   VRB,gap1 /N step   RB )+1)/2)) bits, where N DL   VRB,gap1 =2*min(N gap, N   DL   RB −N gap ). Ngap may be derived from system bandwidth of the concerned serving cell. N step   RB  may be determined from Table 6. 
     
       
         
           
               
               
             
               
                 TABLE 5 
               
               
                   
               
               
                 System Bandwidth (BW) 
                 Precoding resource block group (PRG) size 
               
               
                 N DL RB 
                 P 
               
               
                   
               
             
            
               
                 &lt;=10 
                 1 
               
               
                 11-26 
                 2 
               
               
                 27-63 
                 3 
               
               
                  64-110 
                 4 
               
               
                   
               
            
           
         
       
     
     
       
         
           
               
               
               
             
               
                   
                 TABLE 6 
               
               
                   
                   
               
               
                   
                 System BW 
                   
               
               
                   
                 N DL RB 
                 N step RB 
               
               
                   
                   
               
             
            
               
                   
                 6-49 
                 2 
               
               
                   
                 50-110 
                 4 
               
               
                   
                   
               
            
           
         
       
     
     DCI format 2, 2A, 2B, 2C, 2D may include the bit fields provided in Table 7. 
     
       
         
           
               
               
               
               
               
               
             
               
                   
                 TABLE 7 
               
               
                   
                   
               
               
                   
                 DCI F 2 
                 DCI F 2A 
                 DCI F 2B 
                 DCI F 2C 
                 DCI F 2D 
               
               
                   
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
               
               
            
               
                 CIF 
                 0 or 3 
                 0 or 3 
                 0 or 3 
                 0 or 3 
                 0 or 3 
               
               
                 Resource 
                 1 
                 1 
                 1 
                 1 
                 1 
               
               
                 allocation header 
               
               
                 Resource block 
                 * 
                 * 
                 * 
                 * 
                 * 
               
               
                 assignment 
               
               
                 TPC command for 
                 2 
                 2 
                 2 
                 2 
                 2 
               
               
                 PUCCH 
               
               
                 Downlink 
                 0 (FDD 
                 0 (FDD 
                 0 (FDD 
                 0 (FDD 
                 0 (FDD 
               
               
                 Assignment Index 
                 PCell) or 2 
                 PCell) or 2 
                 PCell) or 2 
                 PCell) or 2 
                 PCell) or 2 
               
               
                   
                 (otherwise) 
                 (otherwise) 
                 (otherwise) 
                 (otherwise) 
                 (otherwise) 
               
               
                 HARQ process 
                 3 (FDD 
                 3 (FDD 
                 3 (FDD 
                 3 (FDD 
                 3 (FDD 
               
               
                 number 
                 PCell) or 4 
                 PCell) or 4 
                 PCell) or 4 
                 PCell) or 4 
                 PCell) or 4 
               
               
                   
                 (TDD 
                 (TDD 
                 (TDD 
                 (TDD 
                 (TDD 
               
               
                   
                 PCell) 
                 PCell) 
                 PCell) 
                 PCell) 
                 PCell) 
               
               
                 Scrambling 
                 N/A 
                 N/A 
                 1 
                 N/A 
                 N/A 
               
               
                 identity 
               
               
                 Antenna port, 
                 N/A 
                 N/A 
                 N/A 
                 3 
                 3 
               
               
                 scrambling 
               
               
                 identity and 
               
               
                 number of layers 
               
               
                 SRS request 
                 N/A 
                 N/A 
                 0 or 1 
                 0 or 1 
                 N/A 
               
               
                 Transport block to 
                 1 
                 1 
                 N/A 
                 N/A 
               
               
                 codeword swap 
               
               
                 flag 
               
               
                 Modulation and 
                 5 
                 5 
                 5 
                 5 
                 5 
               
               
                 coding scheme 
               
               
                 (TB1) 
               
               
                 New data 
                 1 
                 1 
                 1 
                 1 
                 1 
               
               
                 indicator (TB1) 
               
               
                 Redundancy 
                 2 
                 2 
                 2 
                 2 
                 2 
               
               
                 version (TB1) 
               
               
                 Modulation and 
                 5 
                 5 
                 5 
                 5 
                 5 
               
               
                 coding scheme 
               
               
                 (TB2) 
               
               
                 New data 
                 1 
                 1 
                 1 
                 1 
                 1 
               
               
                 indicator (TB2) 
               
               
                 Redundancy 
                 2 
                 2 
                 2 
                 2 
                 2 
               
               
                 version (TB2) 
               
               
                 PDSCH RE 
                 N/A 
                 N/A 
                 N/A 
                 N/A 
                 2 
               
               
                 Mapping and 
               
               
                 Quasi-Co- 
               
               
                 Location Indicator 
               
               
                 Precoding 
                 3 (2 CRS 
                 0 (2 CRS 
                 N/A 
                 N/A 
                 N/A 
               
               
                 information 
                 ports) or 6 
                 ports) or 2 
               
               
                   
                 (4 CRS 
                 (4 CRS 
               
               
                   
                 ports) 
                 ports) 
               
               
                 HARQ-ACK 
                 2 
                 2 
                 2 
                 2 
                 2 
               
               
                 resource offset 
                 (EPDCCH) 
                 (EPDCCH) 
                 (EPDCCH) 
                 (EPDCCH) 
                 (EPDCCH) 
               
               
                   
                 or 0 
                 or 0 
                 or 0 
                 or 0 
                 or 0 
               
               
                   
                 (PDCCH) 
                 (PDCCH) 
                 (PDCCH) 
                 (PDCCH) 
                 (PDCCH) 
               
               
                   
               
            
           
         
       
     
     DCI format 0 and 4 may include the following bit fields as provided in Table 8. 
     
       
         
           
               
               
               
             
               
                   
                 TABLE 8 
               
               
                   
                   
               
               
                   
                 DCI F 0 
                 DCI F 4 
               
               
                   
                   
               
             
            
               
                   
               
            
           
           
               
               
               
            
               
                 CIF 
                 0 or 3 
                 0 or 3 
               
               
                 Flag for format0/1A differentiation 
                 1 
                 N/A 
               
               
                 Frequency hopping flag 
                 1 
                 N/A 
               
               
                 Resource block assignment 
                 **** 
                 ***** 
               
               
                 TPC command for PUSCH 
                 2 
                 2 
               
               
                 Cyclic shift for DM-RS and 
                 3 
                 3 
               
               
                 orthogonal cover code (OCC) 
               
               
                 index 
               
               
                 UL index 
                 2 (TDD conf. 0) 
                 2 (TDD conf. 0) 
               
               
                   
                 or 0 (otherwise) 
                 or 0 (otherwise) 
               
               
                 Downlink Assignment Index 
                 2 (TDD PCell) 
                 2 (TDD PCell) 
               
               
                   
                 or 0 (otherwise) 
                 or 0 (otherwise) 
               
               
                 CSI request 
                 2 (multiple DL 
                 2 (multiple DL 
               
               
                   
                 cells, multiple 
                 cells, multiple 
               
               
                   
                 CSI processes, 
                 CSI processes, 
               
               
                   
                 multiple 
                 multiple 
               
               
                   
                 subframe sets) 
                 subframe sets) 
               
               
                   
                 or 1 (otherwise) 
                 or 1 (otherwise) 
               
               
                 SRS request 
                 0 or 1 
                 2 
               
               
                 Resource allocation type 
                 1 
                 1 
               
               
                 Modulation and coding scheme 
                 5 
                 5 
               
               
                 (TB1) 
               
               
                 New data indicator (TB1) 
                 1 
                 1 
               
               
                 Modulation and coding scheme 
                 N/A 
                 5 
               
               
                 (TB2) 
               
               
                 New data indicator (TB2) 
                 N/A 
                 1 
               
               
                 Precoding information 
                 N/A 
                 3 (2 CRS ports) 
               
               
                   
                   
                 or 6 (4 CRS 
               
               
                   
                   
                 ports) 
               
               
                   
               
            
           
         
       
     
     It should be noted that in Table 8, **** is ceil(log 2 (N UL   RB (N UL   RB +1)/2)) bits. Also, ***** is max(ceil(log 2 (N UL   RB (N UL   RB +1)/2)), ceil(log 2 (C(ceil(N UL   RB /P+1), 4)))) bits, where C(n, r) is a formula for Combinations (i.e., “n choose r”). 
     A PDCCH/EPDCCH search space is also described herein. PDCCH may be transmitted using the first 1 to 4 OFDM symbols in a subframe, while PDCCH may be transmitted using the OFDM symbols starting with the second to the fifth OFDM symbol and ending with the last OFDM symbol in a subframe. Resource element groups (REG) may be used for defining the mapping of control channels to resource elements. 
     A resource-element group may be represented by the index pair (k′,l′) of the resource element with the lowest index k in the group with all resource elements in the group having the same value of l. For example, (k,l=0) with k=k 0 +0,k 0 +1, . . . , k 0 +5 or k=k 0 +6, k 0 +7, . . . , k 0 +11. The set of resource elements (k, l) in a resource-element group depends on the number of cell-specific reference signals configured. Four symbols can be mapped to a single resource-element group. Mapping of a symbol-quadruplet  z(i), z(i+1), z(i+2), z(i+3)  onto a resource-element group represented by resource-element (k′, l′) is defined such that elements z(i) are mapped to resource elements (k, l) of the resource-element group not used for cell-specific reference signals in increasing order of i and k. 
     The physical downlink control channel carries scheduling assignments and other control information. A physical control channel is transmitted on an aggregation of one or several consecutive control channel elements (CCEs), where a control channel element corresponds to 9 resource element groups. The number of resource-element groups not assigned to PCFICH or PHICH is N REG . The CCEs available in the system are numbered from 0 to N CCE −1, where N CCE =└N REG /9]. The PDCCH supports multiple formats. A PDCCH consisting of n consecutive CCEs may only start on a CCE fulfilling i mod n=0, where i is the CCE number. 
     Enhanced resource element groups (EREG) are used for defining the mapping of enhanced control channels to resource elements. There are 16 EREGs, numbered from 0 to 15, per physical resource block pair. All resource elements, except resource elements carrying DM-RS for antenna ports p={107,108,109,110} for normal cyclic prefix or p={107,108} for extended cyclic prefix, may be numbered in a physical resource-block pair cyclically from 0 to 15 in an increasing order of first frequency, then time. All resource elements with number i in that physical resource-block pair constitutes EREG number i. 
     The enhanced physical downlink control channel (EPDCCH) carries scheduling assignments. An EPDCCH may be transmitted using an aggregation of one or several consecutive enhanced control channel elements (ECCEs) where each ECCE includes multiple enhanced resource element groups (EREGs). The number of ECCEs used for one EPDCCH depends on the EPDCCH format. 
     Both localized and distributed transmission may be supported. An EPDCCH can use either localized or distributed transmission, differing in the mapping of ECCEs to EREGs and PRB pairs. 
     The control region of each serving cell includes a set of CCEs, numbered from 0 to N CCE,k −1, where N CCE,k  is the total number of CCEs in the control region of subframe k. The UE  102  may monitor a set of PDCCH candidates on one or more activated serving cells as configured by higher layer signaling for control information, where monitoring implies attempting to decode each of the PDCCHs in the set according to all the monitored DCI formats. 
     The set of PDCCH candidates to monitor are defined in terms of search spaces, where a search space S k   (L)  at aggregation level L ∈ {1,2,4,8} is defined by a set of PDCCH candidates. For each serving cell on which PDCCH is monitored, the CCEs corresponding to PDCCH candidate m of the search space S k   (L)  are given by 
         L {( Y   k   +m′ )mod└ N   CCE,k   /L┘}+i.    (1)
 
     In Equation (1), Y k  is defined below, and i=0, . . . , L−1 . For the common search space (CSS) m′=m . For the PDCCH UE specific search space, for the serving cell on which PDCCH is monitored, if the monitoring UE  102  is configured with a carrier indicator field, then m′=m+M (L) ·n CI  where n CI  is the carrier indicator field value. Otherwise, if the monitoring UE  102  is not configured with a carrier indicator field then m′=m , where m=0, . . . , M (L) −1 . M (L)  is the number of PDCCH candidates to monitor in the given search space. 
     For the common search spaces, Y k  is set to 0 for the two aggregation levels L=4 and L=8. 
     For the UE-specific search space S k   (L)  at aggregation level L, the variable Y k  is defined by 
         Y   k =( A·Y   k-1 )mod  D.    (2)
 
     In Equation (2), Y k-1 =n RNTI ≠0, A=39827, D=65537 and k=└n s/ 2┘, where n s  is the slot number within a radio frame. The Radio Network Temporary Identifier (RNTI) value used for n RNTI  may be any RNTI. 
     The UE  102  may monitor one common search space in every non-discontinuous reception (DRX) subframe at each of the aggregation levels 4 and 8 on the primary cell. If a UE  102  is not configured for EPDCCH monitoring, and if the UE  102  is not configured with a carrier indicator field, then the UE  102  may monitor one PDCCH UE-specific search space at each of the aggregation levels 1, 2, 4, 8 on each activated serving cell in every non-DRX subframe. 
     If a UE  102  is not configured for EPDCCH monitoring, and if the UE  102  is configured with a carrier indicator field, then the UE  102  may monitor one or more UE-specific search spaces at each of the aggregation levels 1, 2, 4, 8 on one or more activated serving cells as configured by higher layer signaling in every non-DRX subframe. 
     If a UE  102  is configured for EPDCCH monitoring on a serving cell, and if that serving cell is activated, and if the UE  102  is not configured with a carrier indicator field, then the UE  102  may monitor one PDCCH UE-specific search space at each of the aggregation levels 1, 2, 4, 8 on that serving cell in all non-DRX subframes where EPDCCH is not monitored on that serving cell. 
     If a UE  102  is configured for EPDCCH monitoring on a serving cell, and if that serving cell is activated, and if the UE  102  is configured with a carrier indicator field, then the UE  102  may monitor one or more PDCCH UE-specific search spaces at each of the aggregation levels 1, 2, 4, 8 on that serving cell as configured by higher layer signaling in all non-DRX subframes where EPDCCH is not monitored on that serving cell. 
     The common and PDCCH UE-specific search spaces on the primary cell may overlap. 
     A UE configured with the carrier indicator field associated with monitoring PDCCH on serving cell c may monitor PDCCH configured with carrier indicator field and with cyclic redundancy check (CRC) scrambled by Cell Radio Network Temporary Identifier (C-RNTI) in the PDCCH UE specific search space of serving cell c. 
     A UE  102  configured with the carrier indicator field associated with monitoring PDCCH on the primary cell may monitor PDCCH configured with carrier indicator field and with CRC scrambled by Semi-Persistent Scheduling (SPS) C-RNTI in the PDCCH UE specific search space of the primary cell. 
     The UE may monitor the common search space for PDCCH without carrier indicator field. For the serving cell on which PDCCH is monitored, if the UE  102  is not configured with a carrier indicator field, it shall monitor the PDCCH UE specific search space for PDCCH without carrier indicator field, if the UE  102  is configured with a carrier indicator field it shall monitor the PDCCH UE specific search space for PDCCH with carrier indicator field. 
     If the UE  102  is not configured with a LAA SCell, the UE  102  is not expected to monitor the PDCCH of a secondary cell if it is configured to monitor PDCCH with carrier indicator field corresponding to that secondary cell in another serving cell. 
     If the UE  102  is configured with a LAA SCell, the UE  102  is not expected to monitor the PDCCH UE specific space of the LAA SCell if it is configured to monitor PDCCH with a carrier indicator field corresponding to that LAA SCell in another serving cell where the UE  102  is not expected to be configured to monitor PDCCH with carrier indicator field in an LAA SCell. Alternatively, the UE  102  is not expected to monitor the PDCCH UE specific space of the LAA SCell if it is configured to monitor PDCCH with a carrier indicator field corresponding to that LAA SCell in another serving cell where the UE  102  is not expected to be scheduled with PDSCH starting in the second slot in a subframe in an LAA SCell if the UE  102  is configured to monitor PDCCH with carrier indicator field corresponding to that LAA SCell in another serving cell. 
     For the serving cell on which PDCCH is monitored, the UE  102  may monitor PDCCH candidates at least for the same serving cell. A UE  102  configured to monitor PDCCH candidates with CRC scrambled by C-RNTI or SPS C-RNTI with a common payload size and with the same first CCE index n CCE  but with different sets of DCI information fields in the common search space or PDCCH UE specific search space on the primary cell may assume that for the PDCCH candidates with CRC scrambled by C-RNTI or SPS C-RNTI, if the UE  102  is configured with the carrier indicator field associated with monitoring the PDCCH on the primary cell, only the PDCCH in the common search space is transmitted by the primary cell. Otherwise, only the PDCCH in the UE specific search space is transmitted by the primary cell. 
     A UE  102  configured to monitor PDCCH candidates in a given serving cell with a given DCI format size with CIF, and CRC scrambled by C-RNTI, where the PDCCH candidates may have one or more possible values of CIF for the given DCI format size, may assume that a PDCCH candidate with the given DCI format size may be transmitted in the given serving cell in any PDCCH UE specific search space corresponding to any of the possible values of CIF for the given DCI format size. 
     If a serving cell is a LAA SCell, and if the higher layer parameter subframeStartPosition for the SCell indicates ‘s07’, the UE  102  monitors PDCCH UE-specific search space candidates on the SCell in both the first and second slots of a subframe. Otherwise, the UE  102  monitors PDCCH UE-specific search space candidates on the SCell in the first slots of a subframe. 
     If a serving cell is a LAA SCell, the UE  102  may receive PDCCH with DCI CRC scrambled by component carrier Radio Network Temporary Identifier (CC-RNTI) on the LAA SCell. The DCI formats that the UE  102  may monitor depend on the configured transmission mode per each serving cell. If a UE  102  is configured with higher layer parameter skipMonitoringDCI-format0-1A for a serving cell, the UE  102  is not required to monitor the PDCCH with DCI Format 0/ 1 A in the UE specific search space for that serving cell. 
     Regarding the EPDCCH search space, for each serving cell, higher layer signaling can configure a UE  102  with one or two EPDCCH-PRB-sets for EPDCCH monitoring. The PRB-pairs corresponding to an EPDCCH-PRB-set are indicated by higher layers. Each EPDCCH-PRB-set may include a set of ECCEs numbered from 0 to N ECCE,p,k −1 where N ECCE,p,k  is the number of ECCEs in EPDCCH-PRB-set p of subframe k. Each EPDCCH-PRB-set can be configured for either localized EPDCCH transmission or distributed EPDCCH transmission. 
     The UE  102  may monitor a set of EPDCCH candidates on one or more activated serving cells as configured by higher layer signaling for control information, where monitoring implies attempting to decode each of the EPDCCHs in the set according to the monitored DCI formats. 
     The UE  102  may monitor a set of EPDCCH candidates on one or more activated serving cells as configured by higher layer signaling for control information. Monitoring may imply attempting to decode each of the EPDCCHs in the set according to the monitored DCI formats. 
     The set of EPDCCH candidates to monitor are defined in terms of EPDCCH UE-specific search spaces. For each serving cell, the subframes in which the UE  102  monitors EPDCCH UE-specific search spaces are configured by higher layers. 
     The UE  102  may not monitor EPDCCH for TDD and normal downlink CP, in special subframes for the special subframe configurations 0 and 5. The UE  102  may not monitor EPDCCH for TDD and extended downlink CP, in special subframes for the special subframe configurations 0, 4 and 7. The UE  102  may not monitor EPDCCH in subframes indicated by higher layers to decode PMCH. The UE  102  may not monitor EPDCCH for TDD and if the UE  102  is configured with different UL/DL configurations for the primary and a secondary cell, in a downlink subframe on the secondary cell when the same subframe on the primary cell is a special subframe and the UE  102  is not capable of simultaneous reception and transmission on the primary and secondary cells. 
     An EPDCCH UE-specific search space ES k   L ) at aggregation level L∈ {1,2,4,8,16,32} is defined by a set of EPDCCH candidates. For an EPDCCH-PRB-set p, the ECCEs corresponding to EPDCCH candidate m of the search space ES k   (L)  are given by 
     
       
         
           
             
               
                 
                   
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     In Equation (3), Y p,k  is defined below, i=0, . . . , L−1, and b=n CI  if the UE  102  is configured with a carrier indicator field for the serving cell on which EPDCCH is monitored, otherwise b=0. Also in Equation (3), n CI  is the carrier indicator field value and m=0,1 . . . M p   (L) −1. 
     If the UE  102  is not configured with a carrier indicator field for the serving cell on which EPDCCH is monitored, M p   (L)  is the number of EPDCCH candidates to monitor at aggregation level L in EPDCCH-PRB-set p for the serving cell on which EPDCCH is monitored. Otherwise, M p   (L)  is the number of EPDCCH candidates to monitor at aggregation level L in EPDCCH-PRB-set p for the serving cell indicated by n CI . 
     The variable Y p,k  is defined by 
         Y   p,k =( A   p   ·Y   p,k-1 )mod  D.    (4)
 
     In Equation (4), Y p,k-1 =n RNTI ≠0, A 0 =39827, A 1 =39829, D=65537 and k=└n s /2┘, where n s  is the slot number within a radio frame. 
     If a UE  102  is configured with higher layer parameter skipMonitoringDCI-format0-1A for a serving cell, the UE  102  is not required to monitor the EPDCCH with DCI Format 0/1A in the UE specific search space for that serving cell. 
     If the UE  102  is not configured with a carrier indicator field, then the UE  102  may monitor one EPDCCH UE-specific search space at each of the aggregation levels on each activated serving cell for which it is configured to monitor EPDCCH. 
     If a UE  102  is configured for EPDCCH monitoring, and if the UE  102  is configured with a carrier indicator field, then the UE  102  may monitor one or more EPDCCH UE-specific search spaces at each of the aggregation levels on one or more activated serving cells as configured by higher layer signaling. 
     A UE  102  configured with the carrier indicator field associated with monitoring EPDCCH on serving cell c may monitor EPDCCH configured with the carrier indicator field and with CRC scrambled by C-RNTI in the EPDCCH UE specific search space of serving cell c. 
     A UE  102  configured with the carrier indicator field associated with monitoring EPDCCH on the primary cell may monitor EPDCCH configured with the carrier indicator field and with CRC scrambled by SPS C-RNTI in the EPDCCH UE specific search space of the primary cell. 
     A UE  102  is not expected to be configured to monitor EPDCCH with a carrier indicator field in an LAA SCell. A UE is not expected to be scheduled with PDSCH starting in the second slot in a subframe in an LAA SCell if the UE  102  is configured to monitor EPDCCH with a carrier indicator field corresponding to that LAA SCell in another serving cell. 
     For the serving cell on which EPDCCH is monitored, if the UE  102  is not configured with a carrier indicator field, it may monitor the EPDCCH UE specific search space for EPDCCH without the carrier indicator field. If the UE  102  is configured with a carrier indicator field it may monitor the EPDCCH UE specific search space for EPDCCH with the carrier indicator field. 
     A UE  102  is not expected to monitor the EPDCCH of a secondary cell if it is configured to monitor EPDCCH with a carrier indicator field corresponding to that secondary cell in another serving cell. For the serving cell on which EPDCCH is monitored, the UE  102  may monitor EPDCCH candidates at least for the same serving cell. 
     A UE  102  configured to monitor EPDCCH candidates in a given serving cell with a given DCI format size with CIF, and CRC scrambled by C-RNTI, where the EPDCCH candidates may have one or more possible values of CIF for the given DCI format size, may assume that an EPDCCH candidate with the given DCI format size may be transmitted in the given serving cell in any EPDCCH UE specific search space corresponding to any of the possible values of CIF for the given DCI format size. 
     For the serving cell on which EPDCCH is monitored, a UE  102  is not required to monitor the EPDCCH in a subframe that is configured by higher layers to be part of a positioning reference signal occasion if the positioning reference signal occasion is only configured within Multimedia Broadcast Single Frequency Network (MBSFN) subframes and the cyclic prefix length used in subframe #0 is a normal cyclic prefix. 
     The UE&#39;s  102  MAC procedure may include the following operations Downlink Shared Channel (DL-SCH) data transfer may include DL assignment reception and HARQ operation. For the DL assignment reception, downlink assignments transmitted on the PDCCH indicate if there is a transmission on a DL-SCH for a particular MAC entity and provide the relevant HARQ information. 
     For the HARQ operation, there may be one HARQ entity at the MAC entity for each serving cell that maintains a number of parallel HARQ processes. Each HARQ process may be associated with a HARQ process identifier. The HARQ entity may direct HARQ information and associated transport blocks (TBs) received on the DL-SCH to the corresponding HARQ processes. If a downlink assignment has been indicated for this transmission time interval (TTI), the MAC entity may allocate the TB(s) received from the physical layer and the associated HARQ information to the HARQ process indicated by the associated HARQ information. If this is a new transmission, the MAC entity may then attempt to decode the received data. If this is a retransmission, the MAC entity may then combine the received data with the data currently in the soft buffer for this TB and attempts to decode the combined data. 
     The UE&#39;s  102  MAC procedure may also include Uplink Shared Channel (UL-SCH) data transfer. This may include a UL grant reception; HARQ operation; and multiplexing and assembly. For UL grant reception, in order to transmit on the UL-SCH the MAC entity must have a valid uplink grant (except for non-adaptive HARQ retransmissions) which it may receive dynamically on the PDCCH or in a random access response or which may be configured semi-persistently. To perform requested transmissions, the MAC layer may receive HARQ information from lower layers. When the physical layer is configured for uplink spatial multiplexing, the MAC layer may receive up to two grants (one per HARQ process) for the same TTI from lower layers. 
     For HARQ operation, there may be one HARQ entity at the MAC entity for each serving cell with a configured uplink, which maintains a number of parallel HARQ processes allowing transmissions to take place continuously while waiting for the HARQ feedback on the successful or unsuccessful reception of previous transmissions. At a given TTI, if an uplink grant is indicated for the TTI, the HARQ entity may identify the HARQ process(es) for which a transmission should take place. It may also route the received HARQ feedback (i.e., acknowledgment (ACK)/negative acknowledgment (NACK) information), modulation and coding scheme (MCS) and resource, relayed by the physical layer, to the appropriate HARQ process(es). For each TTI, the HARQ entity may identify the HARQ process(es) associated with this TTI. 
     For multiplexing and assembly, RRC may control the scheduling of uplink data by signaling for each logical channel. An increasing priority value may indicate a lower priority level, prioritisedBitRate may set the prioritized bit rate (PBR), bucketSizeDuration may set the bucket size duration (BSD). 
     The MAC entity may maintain a variable Bj for each logical channel j. Bj may be initialized to zero when the related logical channel is established, and may be incremented by the product PBR×TTI duration for each TTI, where PBR is the prioritized bit rate of logical channel j. However, the value of Bj may never exceed the bucket size and if the value of Bj is larger than the bucket size of logical channel j, Bj may be set to the bucket size. The bucket size of a logical channel is equal to PBR×BSD, where PBR and BSD are configured by upper layers. 
     When a Scheduling Request (SR) is triggered, it may be considered as pending until it is cancelled. All pending SR(s) may be cancelled and sr-ProhibitTimer may be stopped when a MAC Protocol Data Unit (PDU) is assembled and this PDU includes a Buffer Status Report (BSR) that contains a buffer status up to (and including) the last event that triggered a BSR or, if all pending SR(s) are triggered by a sidelink BSR, when a MAC PDU is assembled and this PDU includes a sidelink BSR which contains buffer status up to (and including) the last event that triggered a sidelink BSR, or, if all pending SR(s) are triggered by a sidelink BSR, when upper layers configure autonomous resource selection, or when the UL grant(s) can accommodate all pending data available for transmission. 
     A buffer status reporting procedure may be used to provide the serving eNB  160  with information about the amount of data available for transmission in the UL buffers associated with the MAC entity. RRC controls BSR reporting by configuring three timers (e.g., periodicBSR-Timer, retxBSR-Timer and logicalChannelSR-ProhibitTimer) and by, for each logical channel, optionally signaling logicalChannelGroup, which allocates the logical channel to a logical channel group (LCG). 
     A power headroom reporting procedure may be used to provide the serving eNB  160  with information about the difference between the nominal UE maximum transmit power and the estimated power for UL-SCH transmission per activated serving cell and also with information about the difference between the nominal UE maximum power and the estimated power for UL-SCH and PUCCH transmission on a SpCell. 
     A solution to reduce latency is shortened round trip time (RTT) for legacy (1 ms) TTI. This covers the cases of carrier aggregation and non-carrier aggregation. For the shortened RTT, an interval between TB reception and HARQ-ACK transmission may be shorter than that of the normal RTT. Alternatively, an interval between HARQ-ACK reception and TB retransmission may be shorter than that of the normal RTT. Or, both of them may be shorter. These may require faster processing. 
     Shortened RTT with 1 ms TTI may apply at least for the case of restricted maximum supported transport block sizes for PDSCH and/or PUSCH when the reduced minimum timing is in operation. Reducing processing time can significantly reduce the user plane latency and improve Transmission Control Protocol (TCP) throughput. Moreover, reducing processing time is useful for delay-sensitive real-time applications. 
     A retransmission cycle of a DL-TB with a shortened RTT timeline is described in connection with  FIG. 10 . A retransmission cycle of a UL-TB with the shortened RTT timeline is described in connection with  FIG. 11 . 
     The shortened RTT may be applied independently of shortened TTI, and they can be applied simultaneously. The dedicated RRC message indicating a configuration of shortened RTT may also include the shortened RTT value or an equivalent such as the value k. The shortened RTT may also be referred to as sRTT, short processing time, short scheduling delay, reduced processing time, processing time reduction, quick HARQ-ACK reporting, or the like. 
     A UE  102  configured with the shortened RTT may still perform the normal RTT-based communication. It should be noted that shortened RTT-based communication may support PDCCH only so that the UE  102  finishes DCI decoding earlier. Alternatively, shortened RTT-based communication may support PDCCH and EPDCCH so that the eNB  160  has more scheduling flexibility. 
     Fallback to normal RTT is also described herein. Even when a UE  102  is configured with shortened RTT-based communication in a serving cell (e.g., PCell, PSCell), the UE  102  may also still be able to perform the normal RTT-based communication in the same serving cell. In other words, shortened RTT-based HARQ processes and normal RTT-based HARQ processes may be able to operate simultaneously between the eNB  160  and the UE  102  in the serving cell. 
     For DL transmissions, there are at least two alternatives from the PDSCH transmission/reception perspective. In a first alternative (A 1 ), an eNB  160  may transmit shortened RTT-based (E)PDCCH/PDSCH and normal RTT-based (E)PDCCH/PDSCH for a single UE  102  in a single subframe. The UE  102  can receive shortened RTT-based (E)PDCCH/PDSCH and normal RTT-based (E)PDCCH/PDSCH in the single subframe. 
     In a second alternative (A 2 ), an eNB  160  may transmit shortened RTT-based (E)PDCCH/PDSCH and normal RTT-based (E)PDCCH/PDSCH for a single UE  102  in different subframes but not in a single subframe. The UE  102  can receive shortened RTT-based (E)PDCCH/PDSCH and normal RTT-based (E)PDCCH/PDSCH in the different subframes but cannot receive (or “is not expected to receive”) them in a single subframe. 
     For DL transmissions, there are two alternatives from the PDSCH associated HARQ-ACK transmission/reception perspective. In a first alternative (B 1 ), a UE  102  may transmit HARQ-ACKs of shortened RTT-based PDSCH and normal RTT-based PDSCH in a single subframe. The eNB  160  can receive HARQ-ACKs of shortened RTT-based PDSCH and normal RTT-based PDSCH from the UE  102  in the single subframe. 
     In a second alternative (B 2 ), a UE  102  may transmit HARQ-ACKs of shortened RTT-based PDSCH and normal RTT-based PDSCH in different subframes but not in a single subframe. The eNB  160  can receive HARQ-ACKs of shortened RTT-based PDSCH and normal RTT-based PDSCH from the UE  102  in the different subframes but is not expected to receive them in a single subframe. 
     Similarly, for UL transmissions, there are two alternatives from the (E)PDCCH/PHICH transmission/reception perspective. In a first alternative (C 1 ), an eNB  160  may transmit shortened RTT-based (E)PDCCH/PHICH and normal RTT-based (E)PDCCH/PHICH for a single UE  102  in a single subframe. The UE  102  can receive shortened RTT-based (E)PDCCH/PHICH and normal RTT-based (E)PDCCH/PHICH in the single subframe. 
     In a second alternative (C 2 ), an eNB  160  may transmit shortened RTT-based (E)PDCCH/PHICH and normal RTT-based (E)PDCCH/PHICH for a single UE  102  in different subframes but not in a single subframe. The UE  102  can receive shortened RTT-based (E)PDCCH/PHICH and normal RTT-based (E)PDCCH/PHICH in the different subframes but cannot receive (or “is not expected to receive”) them in a single subframe. 
     For UL transmissions, there are two alternatives from the PUSCH transmission/reception perspective. In a first alternative (D 1 ), a UE  102  may transmit shortened RTT-based PUSCH and normal RTT-based PUSCH in a single subframe. The eNB  160  can receive shortened RTT-based PUSCH and normal RTT-based PUSCH from the UE  102  in the single subframe. 
     In a second alternative (D 2 ), a UE  102  may transmit shortened RTT-based PUSCH and normal RTT-based PUSCH in different subframes but not in a single subframe. The eNB  160  can receive shortened RTT-based PUSCH and normal RTT-based PUSCH from the UE  102  in the different subframes but is not expected to receive them in a single subframe. 
     Any combination of the alternatives A, B, C, and D is possible, and each of them has its merit. Among them, typical combinations could be [A1, B1, C1, D1], [A1, B2, C1 , D1], [A2, B1, C2, D1], [A2, B2, C2, D1], and [A2, B2, C2, D2]. 
     On alternative A1 and A2, the UE  102  may have to have a knowledge about which RTT-based PDSCH is scheduled in the subframe where (E)PDCCH is detected. There are several approaches for realizing this. 
     In a first approach (Approach 1), search space types are different between shortened RTT and normal RTT. More specifically, when the eNB  160  transmits normal RTT-based PDSCH, the eNB  160  may transmit the corresponding PDCCH (e.g., PDCCH carrying DL assignment which schedules the PDSCH) on a PDCCH CSS. When the eNB  160  transmits shortened RTT-based PDSCH, the eNB  160  may transmit the corresponding (E)PDCCH on an (E)PDCCH UE-specific search space (USS). 
     If the UE  102  detects PDCCH on the PDCCH CSS, the UE  102  may assume that the corresponding PDSCH is a normal RTT-based PDSCH. If the UE  102  detects (E)PDCCH on the (E)PDCCH USS, the UE  102  may assume that the corresponding PDSCH is a shortened RTT-based PDSCH. With this approach, the normal RTT-based PDSCH may be scheduled only by DCI format 1A, while the shortened RTT-based PDSCH may be scheduled by the other DCI formats (e.g., DCI format 2, 2A, 2C, 2D, etc.) as well as DCI format 1A. 
     In a second approach (Approach 2), the search spaces are different between shortened RTT and normal RTT. For example, given that there are M (L)  (E)PDCCH candidates for aggregation level L, the first M 1   (L)  (E)PDCCH candidates may carry DL assignment for the normal RTT-based PDSCH, and the remaining M 2   (L)  (E)PDCCH candidates may carry DL assignment for the shortened RTT-based PDSCH. Here, M 1   (L) +M 2   (L) =M (L) . 
     For another example, M (L)  (E)PDCCH candidates with aggregation level L less than or equal to L t  may carry DL assignment for the normal RTT-based PDSCH, while M (L)  (E)PDCCH candidates with aggregation level L greater than L t  may carry DL assignment for the shortened RTT-based PDSCH. For EPDCCH, this search space separation may be done per EPDCCH PRB set. 
     In a third approach (Approach 3), EPDCCH PRB sets are different between shortened RTT and normal RTT. More specifically, an information element of EPDCCH PRB sets configuration may also be able to include information which indicates that EPDCCHs within the concerned EPDCCH PRB set schedules the shortened RTT-based PDSCH. If the information element does not include this information, EPDCCHs within the concerned EPDCCH PRB set schedules the normal RTT-based PDSCH. If EPDCCH PRB sets, one of which is for the normal RTT base and the other is for the shortened RTT, are overlapped, and if DCI format sizes are the same between those two EPDCCH PRB sets, the UE  102  and the eNB  160  assume the detected EPDCCH may schedule the normal RTT-based PDSCH in order to avoid ambiguity on the RTT type. Alternatively, the detected EPDCCH may schedule the shortened RTT-based PDSCH. 
     In a fourth approach (Approach 4), DCI formats are different between shortened RTT and normal RTT. For example, DCI format sizes are different. For shortened RTT, DCI format for very compact scheduling (e.g., DCI format 1A or 1C or a new DCI format having the same or even smaller size with DCI format 1A or 1C may be used), while the normal DCI format may be used for the normal RTT. To reduce the DCI format size, the new DCI format for the shortened RTT might not have some information field(s) (e.g., Resource block assignment field). Instead, the new DCI format may include an information field indicating for one of several parameter sets that are configured by higher layer signaling such as dedicated RRC signaling. Each of the parameter sets may include Resource block assignment, etc. 
     In a fifth approach (Approach 5), HARQ processes are different between shortened RTT and normal RTT. In one example, the shortened RTT may be configured per HARQ process. More specifically, there are 8 HARQ processes for FDD. The eNB  160  may send the UE  102  a dedicated RRC message indicating the HARQ process numbers for which the shortened RTT applies. The UE  102  configured with the shortened RTT according to the RRC message assumes the shortened RTT for the HARQ process(es) whose HARQ process numbers are indicated. The UE  102  may assume the normal RTT for the other HARQ process(es). Alternatively, the dedicated RRC message may indicate 8-bits-long bitmap information, where the i-th bit corresponds to the i-th HARQ process and indicates whether the shortened RTT applies to the i-th HARQ process or not. In another example, once the UE  102  is configured with shortened RTT, the shortened RTT applies to pre-determined HARQ process(es). Any combination of the above approaches may be applied. 
     Similarly to alternative A1 and A2, also for alternative C1 and C2, the UE  102  may have to have knowledge about which RTT-based PUSCH is scheduled in the subframe where (E)PDCCH is detected. The above-described approaches may be applicable. In this case, PDSCH is replaced by PUSCH; and with the timing difference between PDSCH and the corresponding HARQ-ACK replaced by the timing difference between (E)PDCCH and the corresponding PUSCH and/or the timing difference between PUSCH and the corresponding PHICH. 
     Random Access Response Grant, which is the 20-bit UL Grant indicated by higher layer, may support only PUSCH with normal processing time. 
     The time and frequency resources that can be used by the UE  102  to report channel state information (CSI) which includes Channel Quality Indicator (CQI), precoding matrix indicator (PMI), precoding type indicator (PTI), and/or rank indication (RI) are controlled by the eNB. For spatial multiplexing, the UE  102  may determine a RI corresponding to the number of useful transmission layers. For transmit diversity, RI is equal to one. CSI reporting may be periodic or aperiodic. The UE  102  is configured with resource-restricted CSI measurements if subframe sets are configured by higher layer parameter csi-SubframePatternConfig-r12. The UE  102  in transmission mode  10  can be configured with one or more CSI processes per serving cell by higher layers. Each CSI process is associated with a CSI-RS resource and a CSI-interference measurement (CSI-IM) resource. 
     If a UE  102  is not configured for simultaneous PUSCH and PUCCH transmission, it may transmit periodic CSI reporting on PUCCH in subframes with no PUSCH allocation. If a UE  102  is not configured for simultaneous PUSCH and PUCCH transmission, it may transmit periodic CSI reporting on PUSCH of the serving cell with a smallest ServCelllndex in subframes with a PUSCH allocation, where the UE  102  may use the same PUCCH-based periodic CSI reporting format on PUSCH. In case both periodic and aperiodic CSI reporting would occur in the same subframe, the UE  102  may only transmit the aperiodic CSI report in that subframe. 
     For CSI reporting, a UE  102  may derive for each channel quality indicator (CQI) value reported in uplink subframe n the highest CQI index between 1 and 15 which satisfies the following condition, or CQI index 0 if CQI index 1 does not satisfy the condition that a single PDSCH transport block with a combination of modulation scheme and transport block size corresponding to the CQI index, and occupying a group of downlink physical resource blocks termed the CSI reference resource, could be received with a transport block error probability not exceeding 0.1. 
     Even when the processing time is reduced for PUSCH transmission, CSI calculation may still require an appropriate processing time. Therefore, a CSI reference resource may be defined depending on whether the UE  102  is configured with the processing time reduction or not. 
     To be more specific, with the normal RTT, the CSI reference resource corresponding to CSI reported in a given subframe may be the same valid downlink or valid special subframe as the subframe where the corresponding CSI request is indicated in the DCI format (i.e., UL grant scheduling the normal RTT based PUSCH). Meanwhile, when the UE  102  is configured with the sRTT for the concerned PUSCH, the CSI reference resource corresponding to CSI reported in a given subframe may be allowed to be an earlier (prior) valid downlink or valid special subframe than the subframe where the corresponding CSI request is indicated in the DCI format (i.e., UL grant scheduling the s RTT based PUSCH) in order to ensure sufficient processing time for CSI calculation. 
     For example, the procedure shown in Listing (1) may be used to derive the CSI reference resource for a serving cell when the corresponding CSI is transmitted in subframe n. where n CQI   _   ref  is a timing difference (also referred to as CSI reference resource timing offset) between the CSI reference resource and the CSI reporting subframe and is expressed as the number of subframes. 
     
       
         
           
               
             
               
                   
               
               
                 Listing (1) 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
            
               
                 For a non-BL/CE (bandwidth reduction/coverage enhancement) UE (e.g. a normal 
               
               
                 UE), in the frequency domain, the CSI reference resource is defined by the group of 
               
               
                 downlink physical resource blocks corresponding to the band to which the derived 
               
               
                 CQI value relates. For a BL/CE UE (e.g. a machine type communication (MTC) 
               
               
                 UE), in the frequency domain, the CSI reference resource includes all downlink 
               
               
                 physical resource blocks for any of the narrowband to which the derived CQI value 
               
               
                 relates. 
               
               
                 In the time domain and for a non-BL/CE UE, 
               
               
                 for a UE configured in transmission mode 1-9 or transmission mode 10 with a 
               
               
                 single configured CSI process for the serving cell, the CSI reference resource is 
               
               
                 defined by a single downlink or special subframe n-n CQI     —     ref , 
               
               
                 where for periodic CSI reporting n CQI     —     ref  is the smallest value greater than or 
               
               
                 equal to 4, such that it corresponds to a valid downlink or valid special 
               
               
                 subframe, 
               
               
                 where for aperiodic CSI reporting, if the UE is not configured with the higher 
               
               
                 layer parameter csi-SubframePatternConfig-r12, 
               
               
                 n CQI     —     ref  is such that the reference resource is in the same valid downlink 
               
               
                 or valid special subframe as the corresponding CSI request in an uplink 
               
               
                 DCI format. 
               
               
                 n CQI     —     ref  is equal to 4 and subframe n-n CQI     —     ref  corresponds to a valid 
               
               
                 downlink or valid special subframe, where subframe n-n CQI     —     ref  is received 
               
               
                 after the subframe with the corresponding CSI request in a Random Access 
               
               
                 Response Grant. 
               
               
                 if there is no valid value for n CQI     —     ref  based on the above conditions, then 
               
               
                 n CQI     —     ref  is the smallest value such that the reference resource is in a valid 
               
               
                 downlink or valid special subframe n-n CQI     —     ref  prior to the subframe with 
               
               
                 the corresponding CSI request, where subframe n-n CQI     —     ref  is the lowest 
               
               
                 indexed valid downlink or valid special subframe within a radio frame; 
               
               
                 where for aperiodic CSI reporting, and the UE configured with the higher 
               
               
                 layer parameter csi-SubframePatternConfig-r12, 
               
               
                 for the UE configured in transmission mode 1-9, 
               
               
                 n CQI     —     ref  is the smallest value greater than or equal to 4 and subframe n- 
               
               
                 n CQI     —     ref  corresponds to a valid downlink or valid special subframe, 
               
               
                 where subframe n-n CQI     —     ref  is received on or after the subframe with the 
               
               
                 corresponding CSI request in an uplink DCI format; 
               
               
                 n CQI     —     ref  is the smallest value greater than or equal to 4, and subframe 
               
               
                 n-n CQI     —     ref  corresponds to a valid downlink or valid special subframe, 
               
               
                 where subframe n-n CQI     —     ref  is received after the subframe with the 
               
               
                 corresponding CSI request in an Random Access Response Grant; 
               
               
                 if there is no valid value for n CQI     —     ref  based on the above conditions, 
               
               
                 then n CQI     —     ref  is the smallest value such that the reference resource is in 
               
               
                 a valid downlink or valid special subframe n-n CQI     —     ref  prior to the 
               
               
                 subframe with the corresponding CSI request, where subframe n- 
               
               
                 n CQI     —     ref  is the lowest indexed valid downlink or valid special subframe 
               
               
                 within a radio frame; 
               
               
                 for the UE configured in transmission mode 10, 
               
               
                 n CQI     —     ref  is the smallest value greater than or equal to 4, such that it 
               
               
                 corresponds to a valid downlink or valid special subframe, and the 
               
               
                 corresponding CSI request is in an uplink DCI format; 
               
               
                 n CQI     —     ref  is the smallest value greater than or equal to 4, and subframe 
               
               
                 n-n CQI     —     ref  corresponds to a valid downlink or valid special subframe, 
               
               
                 where subframe n-n CQI     —     ref  is received after the subframe with the 
               
               
                 corresponding CSI request in a Random Access Response Grant; 
               
               
                 for a UE configured in transmission mode 10 with multiple configured CSI 
               
               
                 processes for the serving cell irrespective of whether the UE is configured with 
               
               
                 the processing time reduction for the serving cell, the CSI reference resource for 
               
               
                 a given CSI process is defined by a single downlink or special subframe n- 
               
               
                 n CQI     —     ref , 
               
               
                 where for FDD serving cell and periodic or aperiodic CSI reporting n CQI     —     ref   
               
               
                 is the smallest value greater than or equal to 5, such that it corresponds to a 
               
               
                 valid downlink or valid special subframe, and for aperiodic CSI reporting the 
               
               
                 corresponding CSI request is in an uplink DCI format; 
               
               
                 where for FDD serving cell and aperiodic CSI reporting n CQI     —     ref  is equal to 5 
               
               
                 and subframe n-n CQI     —     ref  corresponds to a valid downlink or valid special 
               
               
                 subframe, where subframe n-n CQI     —     ref  is received after the subframe with the 
               
               
                 corresponding CSI request in a Random Access Response Grant. 
               
               
                 where for TDD serving cell, and 2 or 3 configured CSI processes, and 
               
               
                 periodic or aperiodic CSI reporting, n CQI     —     ref  is the smallest value greater than 
               
               
                 or equal to 4, such that it corresponds to a valid downlink or valid special 
               
               
                 subframe, and for aperiodic CSI reporting the corresponding CSI request is in 
               
               
                 an uplink DCI format; 
               
               
                 where for TDD serving cell, and 2 or 3 configured CSI processes, and 
               
               
                 aperiodic CSI reporting, n CQI     —     ref  is equal to 4 and subframe n-n CQI     —     ref   
               
               
                 corresponds to a valid downlink or valid special subframe, where subframe n- 
               
               
                 n CQI     —     ref  is received after the subframe with the corresponding CSI request in 
               
               
                 a Random Access Response Grant; 
               
               
                 where for TDD serving cell, and 4 configured CSI processes, and periodic or 
               
               
                 aperiodic CSI reporting, n CQI     —     ref  is the smallest value greater than or equal to 
               
               
                 5, such that it corresponds to a valid downlink or valid special subframe, and 
               
               
                 for aperiodic CSI reporting the corresponding CSI request is in an uplink DCI 
               
               
                 format; 
               
               
                 where for TDD serving cell, and 4 configured CSI processes, and aperiodic 
               
               
                 CSI reporting, n CQI     —     ref  is equal to 5 and subframe n-n CQI     —     ref  corresponds to 
               
               
                 a valid downlink or valid special subframe, where subframe n-n CQI     —     ref  is 
               
               
                 received after the subframe with the corresponding CSI request in a Random 
               
               
                 Access Response Grant. 
               
               
                   
               
            
           
         
       
     
     For another example, the procedure shown in Listing (2) may be used to derive the CSI reference resource for a serving cell when the corresponding CSI is transmitted in subframe n. 
     
       
         
           
               
             
               
                   
               
               
                 Listing (2) 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
            
               
                 For a non-BL/CE (bandwidth reduction/coverage enhancement) UE (e.g. a normal 
               
               
                 UE), in the frequency domain, the CSI reference resource is defined by the group of 
               
               
                 downlink physical resource blocks corresponding to the band to which the derived 
               
               
                 CQI value relates. For a BL/CE UE (e.g. a machine type communication (MTC) 
               
               
                 UE), in the frequency domain, the CSI reference resource includes all downlink 
               
               
                 physical resource blocks for any of the narrowband to which the derived CQI value 
               
               
                 relates. 
               
               
                 In the time domain and for a non-BL/CE UE, 
               
               
                 for a UE configured in transmission mode 1-9 or transmission mode 10 with a 
               
               
                 single configured CSI process for the serving cell, the CSI reference resource is 
               
               
                 defined by a single downlink or special subframe n-n CQI     —     ref  , 
               
               
                 where for periodic CSI reporting n CQI     —     ref  is the smallest value greater than or 
               
               
                 equal to 4, such that it corresponds to a valid downlink or valid special 
               
               
                 subframe, 
               
               
                 where for aperiodic CSI reporting, if the UE is not configured with the higher 
               
               
                 layer parameter csi-SubframePatternConfig-r12, or if the UE is not 
               
               
                 configured with the short processing time 
               
               
                 n CQI     —     ref  is such that the reference resource is in the same valid downlink 
               
               
                 or valid special subframe as the corresponding CSI request in an uplink 
               
               
                 DCI format. 
               
               
                 n CQI     —     ref  is equal to 4 and subframe n-n CQI     —     ref  corresponds to a valid 
               
               
                 downlink or valid special subframe, where subframe n-n CQI     —     ref  is received 
               
               
                 after the subframe with the corresponding CSI request in a Random Access 
               
               
                 Response Grant. 
               
               
                 where for aperiodic CSI reporting, and the UE configured with at least either 
               
               
                 the higher layer parameter csi-SubframePatternConfig-r12 or the short 
               
               
                 processing time, 
               
               
                 for the UE configured in transmission mode 1-9, 
               
               
                 n CQI     —     ref  is the smallest value greater than or equal to 4 and subframe n- 
               
               
                 n CQI     —     ref  corresponds to a valid downlink or valid special subframe, 
               
               
                 where subframe n-n CQI     —     ref  is received on or after the subframe with the 
               
               
                 corresponding CSI request in an uplink DCI format; 
               
               
                 n CQI     —     ref  is the smallest value greater than or equal to 4, and subframe 
               
               
                 n-n CQI     —     ref  corresponds to a valid downlink or valid special subframe, 
               
               
                 where subframe n-n CQI     —     ref  is received after the subframe with the 
               
               
                 corresponding CSI request in an Random Access Response Grant; 
               
               
                 if there is no valid value for n CQI     —     ref  based on the above conditions, 
               
               
                 then n CQI     —     ref  is the smallest value such that the reference resource is in 
               
               
                 a valid downlink or valid special subframe n-n CQI     —     ref  prior to the 
               
               
                 subframe with the corresponding CSI request, where subframe n- 
               
               
                 n CQI     —     ref  is the lowest indexed valid downlink or valid special subframe 
               
               
                 within a radio frame; 
               
               
                 for the UE configured in transmission mode 10, 
               
               
                 n CQI     —     ref  is the smallest value greater than or equal to 4, such that it 
               
               
                 corresponds to a valid downlink or valid special subframe, and the 
               
               
                 corresponding CSI request is in an uplink DCI format; 
               
               
                 n CQI     —     ref  is the smallest value greater than or equal to 4, and subframe 
               
               
                 n-n CQI     —     ref  corresponds to a valid downlink or valid special subframe, 
               
               
                 where subframe n-n CQI     —     ref  is received after the subframe with the 
               
               
                 corresponding CSI request in a Random Access Response Grant; 
               
               
                 for a UE configured in transmission mode 10 with multiple configured CSI 
               
               
                 processes for the serving cell irrespective of whether the UE is configured with 
               
               
                 the processing time reduction for the serving cell, the CSI reference resource for 
               
               
                 a given CSI process is defined by a single downlink or special subframe n- 
               
               
                 n CQI     —     ref , 
               
               
                 where for FDD serving cell and periodic or aperiodic CSI reporting n CQI     —     ref   
               
               
                 is the smallest value greater than or equal to 5, such that it corresponds to a 
               
               
                 valid downlink or valid special subframe, and for aperiodic CSI reporting the 
               
               
                 corresponding CSI request is in an uplink DCI format; 
               
               
                 where for FDD serving cell and aperiodic CSI reporting n CQI     —     ref  is equal to 5 
               
               
                 and subframe n-n CQI     —     ref  corresponds to a valid downlink or valid special 
               
               
                 subframe, where subframe n-n CQI     —     ref  is received after the subframe with the 
               
               
                 corresponding CSI request in a Random Access Response Grant. 
               
               
                 where for TDD serving cell, and 2 or 3 configured CSI processes, and 
               
               
                 periodic or aperiodic CSI reporting, n CQI     —     ref  is the smallest value greater than 
               
               
                 or equal to 4, such that it corresponds to a valid downlink or valid special 
               
               
                 subframe, and for aperiodic CSI reporting the corresponding CSI request is in 
               
               
                 an uplink DCI format; 
               
               
                 where for TDD serving cell, and 2 or 3 configured CSI processes, and 
               
               
                 aperiodic CSI reporting, n CQI     —     ref  is equal to 4 and subframe n-n CQI     —     ref   
               
               
                 corresponds to a valid downlink or valid special subframe, where subframe n- 
               
               
                 n CQI     —     ref  is received after the subframe with the corresponding CSI request in 
               
               
                 a Random Access Response Grant; 
               
               
                 where for TDD serving cell, and 4 configured CSI processes, and periodic or 
               
               
                 aperiodic CSI reporting, n CQI     —     ref  is the smallest value greater than or equal to 
               
               
                 5, such that it corresponds to a valid downlink or valid special subframe, and 
               
               
                 for aperiodic CSI reporting the corresponding CSI request is in an uplink DCI 
               
               
                 format; 
               
               
                 where for TDD serving cell, and 4 configured CSI processes, and aperiodic 
               
               
                 CSI reporting, n CQI     —     ref  is equal to 5 and subframe n-n CQI     —     ref  corresponds to 
               
               
                 a valid downlink or valid special subframe, where subframe n-n CQI     —     ref  is 
               
               
                 received after the subframe with the corresponding CSI request in a Random 
               
               
                 Access Response Grant. 
               
               
                   
               
            
           
         
       
     
     For yet another example, the procedure shown in Listing (3) may be used to derive the CSI reference resource for a serving cell when the corresponding CSI is transmitted in subframe n. 
     
       
         
           
               
             
               
                   
               
               
                 Listing (3) 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
            
               
                 For a non-BL/CE (bandwidth reduction/coverage enhancement) UE (e.g. a normal 
               
               
                 UE), in the frequency domain, the CSI reference resource is defined by the group of 
               
               
                 downlink physical resource blocks corresponding to the band to which the derived 
               
               
                 CQI value relates. For a BL/CE UE (e.g. a machine type communication (MTC) 
               
               
                 UE), in the frequency domain, the CSI reference resource includes all downlink 
               
               
                 physical resource blocks for any of the narrowband to which the derived CQI value 
               
               
                 relates. 
               
               
                 In the time domain and for a non-BL/CE UE, 
               
               
                 for a UE configured in transmission mode 1-9 or transmission mode 10 with a 
               
               
                 single configured CSI process for the serving cell, the CSI reference resource is 
               
               
                 defined by a single downlink or special subframe n-n CQI     —     ref , 
               
               
                 where for periodic CSI reporting n CQI     —     ref  is the smallest value greater than or 
               
               
                 equal to 4, such that it corresponds to a valid downlink or valid special 
               
               
                 subframe, 
               
               
                 where for aperiodic CSI reporting, if the UE is not configured with the higher 
               
               
                 layer parameter csi-SubframePatternConfig-r12, and if the UE is not 
               
               
                 configured with the processing time reduction for the serving cell (or if the 
               
               
                 aperiodic CSI reporting is not triggered by the (E)PDCCH which schedules a 
               
               
                 shortened processing time based PUSCH). 
               
               
                 n CQI     —     ref  is such that the reference resource is in the same valid downlink 
               
               
                 or valid special subframe as the corresponding CSI request in an uplink 
               
               
                 DCI format. 
               
               
                 n CQI     —     ref  is equal to 4 and subframe n-n CQI     —     ref  corresponds to a valid 
               
               
                 downlink or valid special subframe, where subframe n-n CQI     —     ref  is received 
               
               
                 after the subframe with the corresponding CSI request in a Random Access 
               
               
                 Response Grant. 
               
               
                 where for aperiodic CSI reporting, if the UE is not configured with the higher 
               
               
                 layer parameter csi-SubframePatternConfig-r12, and if the UE is configured 
               
               
                 with the processing time reduction for the serving cell (or if the aperiodic CSI 
               
               
                 reporting is triggered by the (E)PDCCH which schedules a shortened 
               
               
                 processing time based PUSCH). 
               
               
                 n CQI     —     ref  is the smallest value such that the reference resource is in a valid 
               
               
                 downlink or valid special subframe n-n CQI     —     ref  prior to the subframe with 
               
               
                 the corresponding CSI request, where subframe n-n CQI     —     ref  is the lowest 
               
               
                 indexed valid downlink or valid special subframe (within a radio frame); 
               
               
                 n CQI     —     ref  is equal to 4 and subframe n-n CQI     —     ref  corresponds to a valid 
               
               
                 downlink or valid special subframe, where subframe n-n CQI     —     ref  is received 
               
               
                 after the subframe with the corresponding CSI request in a Random Access 
               
               
                 Response Grant. 
               
               
                 where for aperiodic CSI reporting, and the UE configured with the higher 
               
               
                 layer parameter csi-SubframePatternConfig-r12, 
               
               
                 for the UE configured in transmission mode 1-9 and the UE is not 
               
               
                 configured with the processing time reduction for the serving cell (or the 
               
               
                 aperiodic CSI reporting is not triggered by the (E)PDCCH which schedules 
               
               
                 a shortened processing time based PUSCH), 
               
               
                 n CQI     —     ref  is the smallest value greater than or equal to 4 and subframe n- 
               
               
                 n CQI     —     ref  corresponds to a valid downlink or valid special subframe, 
               
               
                 where subframe n-n CQI     —     ref  is received on or after the subframe with the 
               
               
                 corresponding CSI request in an uplink DCI format; 
               
               
                 n CQI     —     ref  is the smallest value greater than or equal to 4, and subframe 
               
               
                 n-n CQI     —     ref  corresponds to a valid downlink or valid special subframe, 
               
               
                 where subframe n-n CQI     —     ref  is received after the subframe with the 
               
               
                 corresponding CSI request in an Random Access Response Grant; 
               
               
                 if there is no valid value for n CQI     —     ref  based on the above conditions, 
               
               
                 then n CQI     —     ref  is the smallest value such that the reference resource is in 
               
               
                 a valid downlink or valid special subframe n-n CQI     —     ref  prior to the 
               
               
                 subframe with the corresponding CSI request, where subframe n- 
               
               
                 n CQI     —     ref  is the lowest indexed valid downlink or valid special subframe 
               
               
                 within a radio frame; 
               
               
                 for the UE configured in transmission mode 1-9 and the UE is configured 
               
               
                 with the processing time reduction for the serving cell (or the aperiodic 
               
               
                 CSI reporting is triggered by the (E)PDCCH which schedules a shortened 
               
               
                 processing time based PUSCH), 
               
               
                 n CQI     —     ref  is the smallest value such that the reference resource is in a 
               
               
                 valid downlink or valid special subframe n-n CQI     —     ref  prior to the 
               
               
                 subframe with the corresponding CSI request, where subframe n- 
               
               
                 n CQI     —     ref  is the lowest indexed valid downlink or valid special subframe 
               
               
                 (within a radio frame); 
               
               
                 n CQI     —     ref  is the smallest value greater than or equal to 4, and subframe 
               
               
                 n-n CQI     —     ref  corresponds to a valid downlink or valid special subframe, 
               
               
                 where subframe n-n CQI     —     ref  is received after the subframe with the 
               
               
                 corresponding CSI request in an Random Access Response Grant; 
               
               
                 for the UE configured in transmission mode 10 irrespective of whether the 
               
               
                 UE is configured with the processing time reduction for the serving cell, 
               
               
                 n CQI     —     ref  is the smallest value greater than or equal to 4, such that it 
               
               
                 corresponds to a valid downlink or valid special subframe, and the 
               
               
                 corresponding CSI request is in an uplink DCI format; 
               
               
                 n CQI     —     ref  is the smallest value greater than or equal to 4, and subframe 
               
               
                 n-n CQI     —     ref  corresponds to a valid downlink or valid special subframe, 
               
               
                 where subframe n-n CQI     —     ref  is received after the subframe with the 
               
               
                 corresponding CSI request in a Random Access Response Grant; 
               
               
                 for a UE configured in transmission mode 10 with multiple configured CSI 
               
               
                 processes for the serving cell irrespective of whether the UE is configured with 
               
               
                 the processing time reduction for the serving cell, the CSI reference resource for 
               
               
                 a given CSI process is defined by a single downlink or special subframe n- 
               
               
                 n CQI     —     ref , 
               
               
                 where for FDD serving cell and periodic or aperiodic CSI reporting n CQI     —     ref   
               
               
                 is the smallest value greater than or equal to 5, such that it corresponds to a 
               
               
                 valid downlink or valid special subframe, and for aperiodic CSI reporting the 
               
               
                 corresponding CSI request is in an uplink DCI format; 
               
               
                 where for FDD serving cell and aperiodic CSI reporting n CQI     —     ref  is equal to 5 
               
               
                 and subframe n-n CQI     —     ref  corresponds to a valid downlink or valid special 
               
               
                 subframe, where subframe n-n CQI     —     ref  is received after the subframe with the 
               
               
                 corresponding CSI request in a Random Access Response Grant. 
               
               
                 where for TDD serving cell, and 2 or 3 configured CSI processes, and 
               
               
                 periodic or aperiodic CSI reporting, n CQI     —     ref  is the smallest value greater than 
               
               
                 or equal to 4, such that it corresponds to a valid downlink or valid special 
               
               
                 subframe, and for aperiodic CSI reporting the corresponding CSI request is in 
               
               
                 an uplink DCI format; 
               
               
                 where for TDD serving cell, and 2 or 3 configured CSI processes, and 
               
               
                 aperiodic CSI reporting, n CQI     —     ref  is equal to 4 and subframe n-n CQI     —     ref   
               
               
                 corresponds to a valid downlink or valid special subframe, where subframe n- 
               
               
                 n CQI     —     ref  is received after the subframe with the corresponding CSI request in 
               
               
                 a Random Access Response Grant; 
               
               
                 where for TDD serving cell, and 4 configured CSI processes, and periodic or 
               
               
                 aperiodic CSI reporting, n CQI     —     ref  is the smallest value greater than or equal to 
               
               
                 5, such that it corresponds to a valid downlink or valid special subframe, and 
               
               
                 for aperiodic CSI reporting the corresponding CSI request is in an uplink DCI 
               
               
                 format; 
               
               
                 where for TDD serving cell, and 4 configured CSI processes, and aperiodic 
               
               
                 CSI reporting, n CQI     —     ref  is equal to 5 and subframe n-n CQI     —     ref  corresponds to 
               
               
                 a valid downlink or valid special subframe, where subframe n-n CQI     —     ref  is 
               
               
                 received after the subframe with the corresponding CSI request in a Random 
               
               
                 Access Response Grant. 
               
               
                   
               
            
           
         
       
     
     For yet another example, the procedure shown in Listing (4) may be used to derive the CSI reference resource for a serving cell when the corresponding CSI is transmitted in subframe n. 
     
       
         
           
               
             
               
                   
               
               
                 Listing (4) 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
            
               
                 For a non-BL/CE (bandwidth reduction/coverage enhancement) UE (e.g. a normal 
               
               
                 UE), in the frequency domain, the CSI reference resource is defined by the group of 
               
               
                 downlink physical resource blocks corresponding to the band to which the derived 
               
               
                 CQI value relates. For a BL/CE UE (e.g. a machine type communication (MTC) 
               
               
                 UE), in the frequency domain, the CSI reference resource includes all downlink 
               
               
                 physical resource blocks for any of the narrowband to which the derived CQI value 
               
               
                 relates. 
               
               
                 In the time domain and for a non-BL/CE UE, 
               
               
                 for a UE configured in transmission mode 1-9 or transmission mode 10 with a 
               
               
                 single configured CSI process for the serving cell, the CSI reference resource is 
               
               
                 defined by a single downlink or special subframe n-n CQI     —     ref , 
               
               
                 where for periodic CSI reporting n CQI     —     ref  is the smallest value greater than or 
               
               
                 equal to 4, such that it corresponds to a valid downlink or valid special 
               
               
                 subframe, 
               
               
                 where for aperiodic CSI reporting, if the UE is not configured with the higher 
               
               
                 layer parameter csi-SubframePatternConfig-r12, or if aperiodic CSI reporting 
               
               
                 is triggered by an uplink grant which schedules PUSCH with the normal 
               
               
                 processing time, 
               
               
                 n CQI     —     ref  is such that the reference resource is in the same valid downlink 
               
               
                 or valid special subframe as the corresponding CSI request in an uplink 
               
               
                 DCI format. 
               
               
                 n CQI     —     ref  is equal to 4 and subframe n-n CQI     —     ref  corresponds to a valid 
               
               
                 downlink or valid special subframe, where subframe n-n CQI     —     ref  is received 
               
               
                 after the subframe with the corresponding CSI request in a Random Access 
               
               
                 Response Grant. 
               
               
                 where for aperiodic CSI reporting, and if the UE configured with the higher 
               
               
                 layer parameter csi-SubframePatternConfig-r12, or if the aperiodic CSI 
               
               
                 reporting is triggered by an uplink grant which schedules PUSCH with the 
               
               
                 short processing time, 
               
               
                 for the UE configured in transmission mode 1-9, 
               
               
                 n CQI     —     ref  is the smallest value greater than or equal to 4 and subframe n- 
               
               
                 n CQI     —     ref  corresponds to a valid downlink or valid special subframe, 
               
               
                 where subframe n-n CQI     —     ref  is received on or after the subframe with the 
               
               
                 corresponding CSI request in an uplink DCI format; 
               
               
                 n CQI     —     ref  is the smallest value greater than or equal to 4, and subframe 
               
               
                 n-n CQI     —     ref  corresponds to a valid downlink or valid special subframe, 
               
               
                 where subframe n-n CQI     —     ref  is received after the subframe with the 
               
               
                 corresponding CSI request in an Random Access Response Grant; 
               
               
                 if there is no valid value for n CQI     —     ref  based on the above conditions, 
               
               
                 then n CQI     —     ref  is the smallest value such that the reference resource is in 
               
               
                 a valid downlink or valid special subframe n-n CQI     —     ref  prior to the 
               
               
                 subframe with the corresponding CSI request, where subframe n- 
               
               
                 n CQI     —     ref  is the lowest indexed valid downlink or valid special subframe 
               
               
                 within a radio frame; 
               
               
                 for the UE configured in transmission mode 10, 
               
               
                 n CQI     —     ref  is the smallest value greater than or equal to 4, such that it 
               
               
                 corresponds to a valid downlink or valid special subframe, and the 
               
               
                 corresponding CSI request is in an uplink DCI format; 
               
               
                 n CQI     —     ref  is the smallest value greater than or equal to 4, and subframe 
               
               
                 n-n CQI     —     ref  corresponds to a valid downlink or valid special subframe, 
               
               
                 where subframe n-n CQI     —     ref  is received after the subframe with the 
               
               
                 corresponding CSI request in a Random Access Response Grant; 
               
               
                 for a UE configured in transmission mode 10 with multiple configured CSI 
               
               
                 processes for the serving cell irrespective of whether the UE is configured with 
               
               
                 the processing time reduction for the serving cell, the CSI reference resource for 
               
               
                 a given CSI process is defined by a single downlink or special subframe n- 
               
               
                 n CQI     —     ref , 
               
               
                 where for FDD serving cell and periodic or aperiodic CSI reporting n CQI     —     ref   
               
               
                 is the smallest value greater than or equal to 5, such that it corresponds to a 
               
               
                 valid downlink or valid special subframe, and for aperiodic CSI reporting the 
               
               
                 corresponding CSI request is in an uplink DCI format; 
               
               
                 where for FDD serving cell and aperiodic CSI reporting n CQI     —     ref  is equal to 5 
               
               
                 and subframe n-n CQI     —     ref  corresponds to a valid downlink or valid special 
               
               
                 subframe, where subframe n-n CQI     —     ref  is received after the subframe with the 
               
               
                 corresponding CSI request in a Random Access Response Grant. 
               
               
                 where for TDD serving cell, and 2 or 3 configured CSI processes, and 
               
               
                 periodic or aperiodic CSI reporting, n CQI     —     ref  is the smallest value greater than 
               
               
                 or equal to 4, such that it corresponds to a valid downlink or valid special 
               
               
                 subframe, and for aperiodic CSI reporting the corresponding CSI request is in 
               
               
                 an uplink DCI format; 
               
               
                 where for TDD serving cell, and 2 or 3 configured CSI processes, and 
               
               
                 aperiodic CSI reporting, n CQI     —     ref  is equal to 4 and subframe n-n CQI     —     ref   
               
               
                 corresponds to a valid downlink or valid special subframe, where subframe n- 
               
               
                 n CQI     —     ref  is received after the subframe with the corresponding CSI request in 
               
               
                 a Random Access Response Grant; 
               
               
                 where for TDD serving cell, and 4 configured CSI processes, and periodic or 
               
               
                 aperiodic CSI reporting, n CQI     —     ref  is the smallest value greater than or equal to 
               
               
                 5, such that it corresponds to a valid downlink or valid special subframe, and 
               
               
                 for aperiodic CSI reporting the corresponding CSI request is in an uplink DCI 
               
               
                 format; 
               
               
                 where for TDD serving cell, and 4 configured CSI processes, and aperiodic 
               
               
                 CSI reporting, n CQI     —     ref  is equal to 5 and subframe n-n CQI     —     ref  corresponds to 
               
               
                 a valid downlink or valid special subframe, where subframe n-n CQI     —     ref  is 
               
               
                 received after the subframe with the corresponding CSI request in a Random 
               
               
                 Access Response Grant. 
               
               
                   
               
            
           
         
       
     
     A subframe in a serving cell may be considered to be a valid downlink or a valid special subframe if all conditions shown in Listing (5) are satisfied. 
     
       
         
           
               
             
               
                   
               
               
                 Listing (5) 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
            
               
                 it is configured as a downlink subframe or a special subframe for that UE, and 
               
               
                 in case multiple cells with different uplink-downlink configurations are 
               
               
                 aggregated and the UE is not capable of simultaneous reception and 
               
               
                 transmission in the aggregated cells, the subframe in the primary cell is a 
               
               
                 downlink subframe or a special subframe with the length of DwPTS more 
               
               
                 than 7680T s , and 
               
               
                 except for transmission mode 9 or 10, it is not an MBSFN subframe, and 
               
               
                 it does not contain a DwPTS field in case the length of DwPTS is 7680T s  and 
               
               
                 less, and 
               
               
                 it does not fall within a configured measurement gap for that UE, and 
               
               
                 for periodic CSI reporting, it is an element of the CSI subframe set linked to 
               
               
                 the periodic CSI report when that UE is configured with CSI subframe sets, 
               
               
                 and 
               
               
                 for a UE configured in transmission mode 10 with multiple configured CSI 
               
               
                 processes, and aperiodic CSI reporting for a CSI process, it is an element of 
               
               
                 the CSI subframe set linked to the downlink or special subframe with the 
               
               
                 corresponding CSI request in an uplink DCI format, when that UE is 
               
               
                 configured with CSI subframe sets for the CSI process and UE is not 
               
               
                 configured with the higher layer parameter csi-SubframePatternConfig-r12, 
               
               
                 and 
               
               
                 for a UE configured in transmission mode 1-9, and aperiodic CSI reporting, it 
               
               
                 is an element of the CSI subframe set associated with the corresponding CSI 
               
               
                 request in an uplink DCI format, when that UE is configured with CSI 
               
               
                 subframe sets by the higher layer parameter csi-SubframePatternConfig-r12, 
               
               
                 and 
               
               
                 for a UE configured in transmission mode 10, and aperiodic CSI reporting for 
               
               
                 a CSI process, it is an element of the CSI subframe set associated with the 
               
               
                 corresponding CSI request in an uplink DCI format, when that UE is 
               
               
                 configured with CSI subframe sets by the higher layer parameter csi- 
               
               
                 SubframePatternConfig-r12 for the CSI process. 
               
               
                 except if the serving cell is a LAA Scell, and at least one OFDM symbol in 
               
               
                 the subframe is not occupied. 
               
               
                 except if the serving cell is a LAA Scell, and a slot number for discovery 
               
               
                 signal sequence generation is not equal to a normal slot number. 
               
               
                 except if the serving cell is a LAA Scell, and for a UE configured in 
               
               
                 transmission mode 9 or 10, the configured CSI-RS resource associated with 
               
               
                 the CSI process is not in the subframe. 
               
               
                   
               
            
           
         
       
     
     The UE operations module  124  may provide information  148  to the one or more receivers  120 . For example, the UE operations module  124  may inform the receiver(s)  120  when to receive retransmissions. 
     The UE operations module  124  may provide information  138  to the demodulator  114 . For example, the UE operations module  124  may inform the demodulator  114  of a modulation pattern anticipated for transmissions from the eNB  160 . 
     The UE operations module  124  may provide information  136  to the decoder  108 . For example, the UE operations module  124  may inform the decoder  108  of an anticipated encoding for transmissions from the eNB  160 . 
     The UE operations module  124  may provide information  142  to the encoder  150 . The information  142  may include data to be encoded and/or instructions for encoding. For example, the UE operations module  124  may instruct the encoder  150  to encode transmission data  146  and/or other information  142 . The other information  142  may include uplink control information such as PDSCH HARQ-ACK information, CSI and/or scheduling request (SR). 
     The encoder  150  may encode transmission data  146  and/or other information  142  provided by the UE operations module  124 . For example, encoding the data  146  and/or other information  142  may involve error detection and/or correction coding, mapping data to space, time and/or frequency resources for transmission, multiplexing, etc. The encoder  150  may provide encoded data  152  to the modulator  154 . 
     The UE operations module  124  may provide information  144  to the modulator  154 . For example, the UE operations module  124  may inform the modulator  154  of a modulation type (e.g., constellation mapping) to be used for transmissions to the eNB  160 . The modulator  154  may modulate the encoded data  152  to provide one or more modulated signals  156  to the one or more transmitters  158 . 
     The UE operations module  124  may provide information  140  to the one or more transmitters  158 . This information  140  may include instructions for the one or more transmitters  158 . For example, the UE operations module  124  may instruct the one or more transmitters  158  when to transmit a signal to the eNB  160 . For instance, the one or more transmitters  158  may transmit during a UL subframe. The one or more transmitters  158  may upconvert and transmit the modulated signal(s)  156  to one or more eNBs  160 . 
     The UE reduced latency module  126  may reduce latency through the use of a shortened round trip time (RTT). In an implementation, the UE reduced latency module  126  may set, according to a configuration by an eNB  160 , a short processing time for a serving cell. The UE reduced latency module  126  may receive, in a subframe n, a PDCCH. The UE reduced latency module  126  may receive, in the subframe n, a PDSCH corresponding to the PDCCH. The UE reduced latency module  126  may send, in a subframe n+k, a HARQ-ACK corresponding to the PDSCH. In a case that the PDCCH is a PDCCH in common search space, the k may be equal to k 1 . In a case that the PDCCH is a PDCCH in UE-specific search space, the k may be equal to k 2 . The k 2  may be smaller than the k 1 . 
     The UE reduced latency module  126  may control a reception of CSI feedback with the use of a shortened RTT. In an implementation, the UE reduced latency module  126  may configure a short processing time for a serving cell. The UE reduced latency module  126  may receive, in a subframe n, a PDCCH of which a CSI request field is set to trigger an aperiodic CSI report. The UE reduced latency module  126  may transmit, in the subframe n+k, a PUSCH corresponding to the PDCCH, and the aperiodic CSI report is performed on the PUSCH. In a case that the PUSCH is not a PUSCH based on the short processing time, a CSI reference resource may be the subframe n. In a case that the PUSCH is a PUSCH based on the short processing time, a CSI reference resource may be the subframe n+k−n ref . The n ref  is larger than the k. 
     In another implementation, in a case that the k is equal to k 1 , a CSI reference resource may be the subframe n. In a case that the k is smaller than the k 1 , a CSI reference resource may be the subframe n+k−n ref . The n ref  is larger than the k. 
     In yet another implementation, in a case that the PDCCH is a PDCCH in common search space, a CSI reference resource may be the subframe n. In case that the PDCCH is a PDCCH in UE-specific search space, a CSI reference resource may be the subframe n+k−n ref . The n ref  is larger than the k. 
     The eNB  160  may include one or more transceivers  176 , one or more demodulators  172 , one or more decoders  166 , one or more encoders  109 , one or more modulators  113 , a data buffer  162  and an eNB operations module  182 . For example, one or more reception and/or transmission paths may be implemented in an eNB  160 . For convenience, only a single transceiver  176 , decoder  166 , demodulator  172 , encoder  109  and modulator  113  are illustrated in the eNB  160 , though multiple parallel elements (e.g., transceivers  176 , decoders  166 , demodulators  172 , encoders  109  and modulators  113 ) may be implemented. 
     The transceiver  176  may include one or more receivers  178  and one or more transmitters  117 . The one or more receivers  178  may receive signals from the UE  102  using one or more antennas  180   a - n.  For example, the receiver  178  may receive and downconvert signals to produce one or more received signals  174 . The one or more received signals  174  may be provided to a demodulator  172 . The one or more transmitters  117  may transmit signals to the UE  102  using one or more antennas  180   a - n.  For example, the one or more transmitters  117  may upconvert and transmit one or more modulated signals  115 . 
     The demodulator  172  may demodulate the one or more received signals  174  to produce one or more demodulated signals  170 . The one or more demodulated signals  170  may be provided to the decoder  166 . The eNB  160  may use the decoder  166  to decode signals. The decoder  166  may produce one or more decoded signals  164 ,  168 . For example, a first eNB-decoded signal  164  may comprise received payload data, which may be stored in a data buffer  162 . A second eNB-decoded signal  168  may comprise overhead data and/or control data. For example, the second eNB-decoded signal  168  may provide data (e.g., PDSCH HARQ-ACK information and/or CSI) that may be used by the eNB operations module  182  to perform one or more operations. 
     In general, the eNB operations module  182  may enable the eNB  160  to communicate with the one or more UEs  102 . The eNB operations module  182  may include one or more of an eNB reduced latency module  194 . 
     The eNB reduced latency module  194  may reduce latency through the use of a shortened round trip time (RTT). In an implementation, the eNB reduced latency module  194  may configure, in a UE  102 , a short processing time for a serving cell. The eNB reduced latency module  194  may transmit, in a subframe n, a PDCCH. The eNB reduced latency module  194  may transmit, in the subframe n, a PDSCH corresponding to the PDCCH. The eNB reduced latency module  194  may obtain, in a subframe n+k, a HARQ-ACK corresponding to the PDSCH. In a case that the PDCCH is a PDCCH in common search space, the k may be equal to k 1 . In a case that the PDCCH is a PDCCH in UE-specific search space, the k may be equal to k 2 . The k 2  may be smaller than the k 1 . 
     The eNB reduced latency module  194  may control a reception of CSI feedback with the use of a shortened RTT. In an implementation, the eNB reduced latency module  194  may configure, in a UE  102 , a short processing time for a serving cell. The eNB reduced latency module  194  may transmit, in a subframe n, a PDCCH of which a CSI request field is set to trigger an aperiodic CSI report. The eNB reduced latency module  194  may receive, in the subframe n+k, a PUSCH corresponding to the PDCCH, and the aperiodic CSI report is performed on the PUSCH. In a case that the PUSCH is not a PUSCH based on the short processing time, a CSI reference resource may be the subframe n. In a case that the PUSCH is a PUSCH based on the short processing time, a CSI reference resource may be the subframe n+k−n ref . The n ref  is larger than the k. 
     In another implementation, in a case that the k is equal to k 1 , a CSI reference resource may be the subframe n. In a case that the k is smaller than the k 1 , a CSI reference resource may be the subframe n+k−n ref . The n ref  is larger than the k. 
     In yet another implementation, in a case that the PDCCH is a PDCCH in common search space, a CSI reference resource may be the subframe n. In case that the PDCCH is a PDCCH in UE-specific search space, a CSI reference resource may be the subframe n+k−n ref . The n ref  is larger than the k. 
     The eNB operations module  182  may provide information  188  to the demodulator  172 . For example, the eNB operations module  182  may inform the demodulator  172  of a modulation pattern anticipated for transmissions from the UE(s)  102 . 
     The eNB operations module  182  may provide information  186  to the decoder  166 . For example, the eNB operations module  182  may inform the decoder  166  of an anticipated encoding for transmissions from the UE(s)  102 . 
     The eNB operations module  182  may provide information  101  to the encoder  109 . The information  101  may include data to be encoded and/or instructions for encoding. For example, the eNB operations module  182  may instruct the encoder  109  to encode information  101 , including transmission data  105 . 
     The encoder  109  may encode transmission data  105  and/or other information included in the information  101  provided by the eNB operations module  182 . For example, encoding the data  105  and/or other information included in the information  101  may involve error detection and/or correction coding, mapping data to space, time and/or frequency resources for transmission, multiplexing, etc. The encoder  109  may provide encoded data  111  to the modulator  113 . The transmission data  105  may include network data to be relayed to the UE  102 . 
     The eNB operations module  182  may provide information  103  to the modulator  113 . This information  103  may include instructions for the modulator  113 . For example, the eNB operations module  182  may inform the modulator  113  of a modulation type (e.g., constellation mapping) to be used for transmissions to the UE(s)  102 . The modulator  113  may modulate the encoded data  111  to provide one or more modulated signals  115  to the one or more transmitters  117 . 
     The eNB operations module  182  may provide information  192  to the one or more transmitters  117 . This information  192  may include instructions for the one or more transmitters  117 . For example, the eNB operations module  182  may instruct the one or more transmitters  117  when to (or when not to) transmit a signal to the UE(s)  102 . The one or more transmitters  117  may upconvert and transmit the modulated signal(s)  115  to one or more UEs  102 . 
     It should be noted that a DL subframe may be transmitted from the eNB  160  to one or more UEs  102  and that a UL subframe may be transmitted from one or more UEs  102  to the eNB  160 . Furthermore, both the eNB  160  and the one or more UEs  102  may transmit data in a standard special subframe. 
     It should also be noted that one or more of the elements or parts thereof included in the eNB(s)  160  and UE(s)  102  may be implemented in hardware. For example, one or more of these elements or parts thereof may be implemented as a chip, circuitry or hardware components, etc. It should also be noted that one or more of the functions or methods described herein may be implemented in and/or performed using hardware. For example, one or more of the methods described herein may be implemented in and/or realized using a chipset, an application-specific integrated circuit (ASIC), a large-scale integrated circuit (LSI) or integrated circuit, etc. 
       FIGS. 2A and 2B  are block diagrams illustrating a detailed configuration of an eNB  260  and a UE  202  in which systems and methods for low latency radio communications may be implemented. In  FIG. 2A , the eNB  260  may include a higher layer processor  223   a,  a DL transmitter  225  (also referred to as a physical layer transmitter) and a UL receiver  239  (also referred to as a physical layer receiver). The higher layer processor  223   a  may communicate with the DL transmitter  225 , UL receiver  239  and subsystems of each. 
     The DL transmitter  225  may include a control channel transmitter  227  (also referred to as a physical downlink control channel transmitter), a shared channel transmitter  233  (also referred to as a physical downlink shared channel transmitter), and a reference signal transmitter  229  (also referred to as a physical signal transmitter). The DL transmitter  225  may transmit signals/channels to a UE  202  using a transmission antenna  235   a.    
     The UL receiver  239  may include a control channel receiver  241  (also referred to as a physical uplink control channel receiver), a shared channel receiver  247  (also referred to as a physical uplink shared channel receiver), and a reference signal receiver  243  (also referred to as a physical signal receiver). The UL receiver  239  may receive signals/channels from the UE  202  using a receiving antenna  237   a.  The control channel receiver  241  and the shared channel receiver  247  may extract uplink control information (UCI) from a channel and deliver the extracted UCI to the higher layer processor  223   a.    
     The eNB  260  may configure, in a UE  202 , shortened RTT for a serving cell. The configuration may be performed by the higher layer processor  223   a.  The higher layer processor  223   a  may also control the DL transmitter  225  and UL receiver  239  based on the configuration. To be more specific, the higher layer processor  223   a  may control transmission and reception timing of the physical layer transmitter and receiver. The higher layer processor  223   a  may utilize the UCI for subsequent data scheduling. 
     Upon the configuration, the eNB  260  may use the normal RTT and the shortened RTT for communication with the UE  202 . More specifically, a HARQ process for the normal RTT-based transmission and a HARQ process for the shortened RTT-based transmission may run simultaneously on the serving cell for DL and/or UL. Moreover, the eNB  260  and the UE  202  may assume different CSI reference resource timing offsets for the normal RTT-based transmission and for the shortened RTT-based transmission. 
     In  FIG. 2B , the UE  202  may include a higher layer processor  223   b,  a DL (SL) receiver  249  (also referred to as a physical layer receiver) and a UL (SL) transmitter  259  (also referred to as a physical layer transmitter). The higher layer processor  223   b  may communicate with the DL (SL) receiver  249 , UL (SL) transmitter  259  and subsystems of each. 
     The DL (SL) receiver  249  may include a control channel receiver  251  (also referred to as a physical downlink control channel receiver), a shared channel receiver  257  (also referred to as a physical downlink shared channel receiver), and a reference signal receiver  253  (also referred to as a physical signal transmitter). The DL (SL) receiver  249  may receive signals/channels from the eNB  260  using a receiving antenna  237   b.    
     The UL (SL) transmitter  259  may include control channel transmitter  261  (also referred to as a physical uplink control channel transmitter), a shared channel transmitter  267  (also referred to as a physical uplink shared channel transmitter), and a reference signal transmitter  263  (also referred to as a physical signal receiver). The UL (SL) transmitter  259  may send signals/channels to the eNB  260  using a transmission antenna  235   b.    
     The UE  202  may configure (e.g., acquire a configuration of) shortened RTT for a serving cell. The configuration may be performed by the higher layer processor  223   b.  The higher layer processor  223   b  may also control the physical layer transmitter and receiver based on the configuration. To more specific, the higher layer processor  223   b  may control transmission and reception timing as well as UCI multiplexing of the physical layer transmitter and receiver. 
     Upon the configuration, the UE  202  may use the normal RTT and the shortened RTT for communication with the UE  202 . More specifically, a HARQ process for the normal RTT-based transmission and a HARQ process for the shortened RTT-based transmission may run simultaneously on the serving cell for DL and/or UL. 
     In an example, the eNB  260  and the UE  202  may have the following structures to support the approach 1 for DL HARQ RTT reduction. The eNB  260  may comprise a higher-layer processor  223   a  that configures, for the UE  202 , a short processing time for DL HARQ. The UE  202  may comprise a higher-layer processor  223   b  that configures the short processing time. 
     The eNB  260  may also comprise the PDCCH transmitter (e.g., control channel transmitter  227 ) that transmits, in a subframe n, a PDCCH. The UE  202  may also comprise the PDCCH receiver (e.g., control channel receiver  251 ) that receives (monitors), in the subframe n, the PDCCH. A CSI request field of the PDCCH may be set to trigger an aperiodic CSI report. The UE  202  may also comprise the reference signal receiver  253  that performs CSI measurements using downlink reference signals and delivers the CSI to either the shared channel transmitter  267  or the control channel transmitter  261  depending on whether the CSI is periodic or aperiodic and whether a PUSCH is scheduled or not. 
     The eNB  260  may also comprise the PUSCH receiver (e.g., shared channel receiver  247 ) configured to receive, in the subframe n+k, the PUSCH corresponding to the PDCCH. The aperiodic CSI report being performed on the PUSCH. The UE  202  may also comprise the PUSCH transmitter (e.g., shared channel transmitter  267 ) that transmits, in the subframe n+k, the corresponding PUSCH upon the detection of the PDCCH. 
     The UE  202  may comprise the uplink transmitter  259  that feeds back, in the subframe n+k, a CSI reporting. The eNB  260  may comprise the uplink receiver  239  that obtains, in the subframe n+k, the CSI reporting. 
     In a case that the PUSCH is not a PUSCH based on the short processing time, a CSI reference resource is the subframe n. In a case that the PUSCH is a PUSCH based on the short processing time, a CSI reference resource is the subframe n+k−n ref , where the n ref  is larger than the k. 
     Alternatively, in a case that the k is equal to k 1 , a CSI reference resource is the subframe n. In a case that k is smaller than the k 1 , a CSI reference resource is the subframe n+k−n ref , where the n ref  is larger than the k. 
     Alternatively, in a case that the PDCCH is a PDCCH in common search space, the CSI reference resource is the subframe n. In a case that the PDCCH is a PDCCH in UE-specific search space, a CSI reference resource is the subframe n+k−n ref , where the n ref  is larger than the k. Moreover, if the UE  202  is not configured with the short processing time, the CSI reference resource is the subframe n. 
     From another perspective, the eNB  260  may comprise a higher-layer processor  223   a  that configures, for the UE  202 , a short processing time. The UE  202  may comprise a higher-layer processor  223   b  that configures the short processing time. The eNB  260  may also comprise the PDCCH transmitter that transmits a PDCCH. The UE  202  may also comprise the PDCCH receiver that receives (monitors) the PDCCH. The eNB  260  may also comprise the PDSCH transmitter configured to transmit, in the same subframe, the PDSCH corresponding to the PDCCH. The UE  202  may also comprise the PDSCH receiver that receives, in the same subframe, the corresponding PDSCH upon the detection of the PDCCH. The UE  202  may comprise the uplink transmitter  259  that feeds back, in the subframe n, a HARQ-ACK indicating the result of the PDSCH decoding (ACK for successful decoding; NACK for unsuccessful decoding). The eNB  260  may comprise the uplink receiver  239  that obtains, in the subframe n, the HARQ-ACK. 
     In a case that the PDCCH is a PDCCH in common search space, the HARQ-ACK in the subframe n corresponds to the PDSCH in subframe n-k 1 . In a case that the PDCCH is a PDCCH in UE-specific search space, the HARQ-ACK in the subframe n corresponds to the PDSCH in subframe n-k 2 , where the k 2  is smaller than the k 1 . Moreover, if the UE  202  is not configured with the short processing time, and if the HARQ-ACK in the subframe n corresponds to the PDSCH in the subframe n-k, the k is equal to k 1 . 
     In another example, the eNB  260  and the UE  202  may have the following structures to support the approach 1 for UL HARQ RTT reduction. The eNB  260  may comprise a higher-layer processor  223   a  that configures, for the UE  202 , a short processing time for UL HARQ. The UE  202  may comprise a higher-layer processor  223   b  that configures the short processing time. The eNB  260  may also comprise the PDCCH transmitter that transmits, in a subframe n, a PDCCH. The UE  202  may also comprise the PDCCH receiver that receives (monitors), in the subframe n, the PDCCH. The UE  202  may also comprise the PUSCH transmitter that transmits, in the subframe n+k, the PUSCH corresponding to the PDCCH upon the detection of the PDCCH. The eNB  260  may also comprise the PUSCH receiver configured to receive, in the subframe n+k, the PDSCH corresponding to the PDCCH. 
     In a case that the PDCCH is a PDCCH in common search space, the k is equal to k 1 . In a case that the PDCCH is a PDCCH in UE-specific search space, the k is equal to k 2 , where the k 2  is smaller than the k 1 . Moreover, if the UE  202  is not configured with the short processing time, and if the PUSCH in the subframe n+k corresponds to the PDCCH in the subframe n, the k is equal to k 1 . 
     From another perspective, the eNB  260  may comprise a higher-layer processor  223   a  that configures, for the UE  202 , a short processing time for UL HARQ. The UE  202  may comprise a higher-layer processor  223   b  that configures the short processing time. The eNB  260  may also comprise the PDCCH transmitter that transmits a PDCCH. The UE  202  may also comprise the PDCCH receiver that receives (monitors) the PDCCH. The UE  202  may also comprise the PUSCH transmitter that transmits, in the subframe n, the PUSCH corresponding to the PDCCH in subframe n-k upon the detection of the PDCCH in the subframe n-k. The eNB  260  may also comprise the PUSCH receiver configured to receive, in the subframe n, the PDSCH. 
     In a case that the PUSCH is scheduled by a PDCCH in common search space, the PUSCH in the subframe n corresponds to the PDCCH in subframe n-k 1 . In a case that the PUSCH is scheduled by a PDCCH in UE-specific search space, the PUSCH in the subframe n corresponds to the PDCCH in subframe n-k 2 , where the k 2  is smaller than the k 1 . Moreover, if the UE  202  is not configured with the short processing time, and if the PUSCH in the subframe n corresponds to the PDCCH in the subframe n-k, where k is equal to the k 1 . 
     In yet another example, the eNB  260  and the UE  202  may have the following structures to support the approach 1 for UL HARQ RTT reduction. The eNB  260  may comprise a higher-layer processor  223   a  that configures, for the UE  202 , a short processing time for UL HARQ. The UE  202  may comprise a higher-layer processor  223   b  that configures the short processing time. The UE  202  may also comprise the PUSCH transmitter that transmits, in the subframe n, the PUSCH corresponding to the PDCCH upon the detection of the PDCCH. The eNB  260  may also comprise the PUSCH receiver configured to receive, in the subframe n, the PDSCH corresponding to the PDCCH. The eNB  260  may also comprise the control channel transmitter that transmits, in a subframe n+k, a PHICH. The UE  202  may also comprise the control channel receiver that receives (monitors), in the subframe n+k, the PHICH. 
     In a case that the PUSCH is scheduled by a PDCCH in common search space, the k is equal to k 1 . In a case that the PUSCH is scheduled by a PDCCH in UE-specific search space, the k is equal to k 2 , where the k 2  is smaller than the k 1 . Moreover, if the UE  202  is not configured with the short processing time, and if the PHICH in the subframe n+k corresponds to the PUSCH in the subframe n, the k is equal to k 1 . 
     It should be noted that, although “k” is used multiple times in the above explanations, its values could change according to the context and is not necessarily the same. Similarly, although “n” is used multiple times in the above explanations, its values could change according to the context and is not necessarily the same. 
       FIG. 3  is a flow diagram illustrating a method  300  by a UE  102 . The UE  102  may communicate with one or more eNBs  160  in a wireless communication network. In one implementation, the wireless communication network may include an LTE network. 
     The UE  102  may configure  302  a short processing time. For example, the UE  102  may configure  302  a shortened RTT for a serving cell on the basis of a message from the eNB  160 . The configurations may be performed by a higher layer processor  223   b.    
     The UE  102  may receive  304 , in a subframe n, a physical downlink control channel (PDCCH). For example, the UE  102  may include a control channel receiver  251  that receives  304  (monitors), in the subframe n, the PDCCH. A CSI request field of the PDCCH may be set to trigger an aperiodic CSI report. 
     The UE  102  may transmit  306 , in the subframe n+k, a physical uplink shared channel (PUSCH) corresponding to the PDCCH. For example, the UE  102  may include a shared channel transmitter  267  that transmits, in the subframe n+k, the corresponding PUSCH upon the detection of the PDCCH. The aperiodic CSI report may be performed on the PUSCH if the aperiodic CSI report is triggered. 
     In a case that the PUSCH is not a PUSCH based on the short processing time, a CSI reference resource for the aperiodic CSI report is the subframe n. In a case that the PUSCH is a PUSCH based on the short processing time, the CSI reference resource is the subframe n+k−n ref . The n ref  is larger than the k. 
       FIG. 4  is a flow diagram illustrating a method  400  by an eNB  160 . The eNB  160  may communicate with one or more UEs  102  in a wireless communication network. In one implementation, the wireless communication network may include an LTE network. 
     The eNB  160  may configure  402 , in a UE  102 , a short processing time. For example, the eNB  160  may include a higher-layer processor  223   a  that configures, for the UE  102 , a short processing time for the UL HARQ. 
     The eNB  160  may transmit  404 , in a subframe n, a PDCCH. For example, the eNB  160  may include a PDCCH transmitter (e.g., control channel transmitter  227 ) that transmits PDCCH in a subframe n. A CSI request field of the PDCCH may be set to trigger an aperiodic CSI report. 
     The eNB  160  may receive  406 , in the subframe n+k, a PUSCH corresponding to the PDCCH. For example, the eNB  160  may include a PUSCH receiver (e.g., shared channel receiver  247 ) configured to receive, in the subframe n+k, the PUSCH corresponding to the PDCCH. The aperiodic CSI report may be performed on the PUSCH if the aperiodic CSI report is triggered. 
     In a case that PUSCH is not a PUSCH based on the short processing time, the CSI reference resource for the aperiodic CSI report is the subframe n. In a case that PUSCH is a PUSCH based on the short processing time, the CSI reference resource is the subframe n+k−n ref . The n ref  is larger than the k. 
       FIG. 5  is a diagram illustrating one example of a radio frame  581  that may be used in accordance with the systems and methods disclosed herein. This radio frame  581  structure illustrates a TDD structure. Each radio frame  581  may have a length of T f =307200·T s =10 ms, where T f  is a radio frame  581  duration and T s  is a time unit equal to 
     
       
         
           
             1 
             
               ( 
               
                 15000 
                 × 
                 2048 
               
               ) 
             
           
         
       
     
     seconds. The radio frame  581  may include two half-frames  579 , each having a length of 153600·T s =5 ms. Each half-frame  579  may include five subframes  569   a - e,    569   f - j  each having a length of 30720·T s =1 ms. Each subframe  569  may include two slots  583  each having a length of 15360·T s =½ ms. 
     TDD UL/DL configurations 0-6 are given below in Table 9 (from Table 4.2-2 in 3GPP TS 36.211). UL/DL configurations with both 5 millisecond (ms) and 10 ms downlink-to-uplink switch-point periodicity may be supported. In particular, seven UL/DL configurations are specified in 3GPP specifications, as shown in Table 9 below. In Table 9, “D” denotes a downlink subframe, “S” denotes a special subframe and “U” denotes a UL subframe. 
     
       
         
           
               
               
               
             
               
                 TABLE 9 
               
             
            
               
                   
               
               
                 TDD 
                 Downlink- 
                   
               
               
                 UL/DL 
                 to-Uplink 
               
               
                 Config- 
                 Switch- 
               
               
                 uration 
                 Point 
                 Subframe Number 
               
            
           
           
               
               
               
               
               
               
               
               
               
               
               
               
            
               
                 Number 
                 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 
               
               
                   
               
            
           
         
       
     
     In Table 9 above, for each subframe in a radio frame, “D” indicates that the subframe is reserved for downlink transmissions, “U” indicates that the subframe is reserved for uplink transmissions and “S” indicates a special subframe with three fields: a downlink pilot time slot (DwPTS), a guard period (GP) and an uplink pilot time slot (UpPTS). The length of DwPTS and UpPTS is given in Table 10 (from Table 4.2-1 of 3GPP TS 36.211) subject to the total length of DwPTS, GP and UpPTS being equal to 30720·T s =1 ms. In Table 10, “cyclic prefix” is abbreviated as “CP” and “configuration” is abbreviated as “Config” for convenience. 
     
       
         
           
               
               
               
             
               
                   
                 TABLE 10 
               
             
            
               
                   
                   
               
               
                   
                 Normal CP in downlink 
                 Extended CP in downlink 
               
            
           
           
               
               
               
               
            
               
                   
                 UpPTS 
                   
                 UpPTS 
               
            
           
           
               
               
               
               
               
               
               
            
               
                 Special 
                   
                 Normal 
                 Extended 
                   
                 Normal 
                 Extended 
               
               
                 Subframe 
                   
                 CP in 
                 CP in 
                   
                 CP in 
                 CP in 
               
               
                 Config 
                 DwPTS 
                 uplink 
                 uplink 
                 DwPTS 
                 uplink 
                 uplink 
               
               
                   
               
               
                 0 
                  6592 · T s   
                 2192 · T s   
                 2560 · T s   
                  7680 · T s   
                 2192 · T s   
                 2560 · T s   
               
               
                 1 
                 19760 · T s   
                   
                   
                 20480 · T s   
               
               
                 2 
                 21952 · T s   
                   
                   
                 23040 · T s   
               
               
                 3 
                 24144 · T s   
                   
                   
                 25600 · T s   
               
               
                 4 
                 26336 · T s   
                   
                   
                  7680 · T s   
                 4384 · T s   
                 5120 · T s   
               
               
                 5 
                  6592 · T s   
                 4384 · T s   
                 5120 · T s   
                 20480 · T s   
               
               
                 6 
                 19760 · T s   
                   
                   
                 23040 · T s   
               
               
                 7 
                 21952 · T s   
                   
                   
                 — 
                 — 
                 — 
               
               
                 8 
                 24144 · T s   
                   
                   
                 — 
                 — 
                 — 
               
               
                   
               
            
           
         
       
     
     UL/DL configurations with both 5 ms and 10 ms downlink-to-uplink switch-point periodicity are supported. In the case of 5 ms downlink-to-uplink switch-point periodicity, the special subframe exists in both half-frames. In the case of 10 ms downlink-to-uplink switch-point periodicity, the special subframe exists in the first half-frame only. Subframes 0 and 5 and DwPTS may be reserved for downlink transmission. UpPTS and the subframe immediately following the special subframe may be reserved for uplink transmission. 
     In accordance with the systems and methods disclosed herein, some types of subframes  569  that may be used include a downlink subframe, an uplink subframe and a special subframe  577 . In the example illustrated in  FIG. 5 , which has a 5 ms periodicity, two standard special subframes  577   a - b  are included in the radio frame  581 . The remaining subframes  569  are normal subframes  585 . 
     The first special subframe  577   a  includes a downlink pilot time slot (DwPTS)  571   a,  a guard period (GP)  573   a  and an uplink pilot time slot (UpPTS)  575   a.  In this example, the first standard special subframe  577   a  is included in subframe one  569   b.  The second standard special subframe  577   b  includes a downlink pilot time slot (DwPTS)  571   b,  a guard period (GP)  573   b  and an uplink pilot time slot (UpPTS)  575   b.  In this example, the second standard special subframe  577   b  is included in subframe six  569   g.  The length of the DwPTS  571   a - b  and UpPTS  575   a - b  may be given by Table 4.2-1 of 3GPP TS 36.211 (illustrated in Table 10 above) subject to the total length of each set of DwPTS  571 , GP  573  and UpPTS  575  being equal to 30720·T s =1 ms. 
     Each subframe i  569   a - j  (where i denotes a subframe ranging from subframe zero  569   a  (e.g., 0) to subframe nine  569   j  (e.g., 9) in this example) is defined as two slots, 2i and 2i+1 of length T slot =15360·T s =0.5 ms in each subframe  569 . For example, subframe zero (e.g., 0)  569   a  may include two slots, including a first slot. 
     UL/DL configurations with both 5 ms and 10 ms downlink-to-uplink switch-point periodicity may be used in accordance with the systems and methods disclosed herein.  FIG. 5  illustrates one example of a radio frame  581  with 5 ms switch-point periodicity. In the case of 5 ms downlink-to-uplink switch-point periodicity, each half-frame  579  includes a standard special subframe  577   a - b.  In the case of 10 ms downlink-to-uplink switch-point periodicity, a special subframe  577  may exist in the first half-frame  579  only. 
     Subframe zero (e.g., 0)  569   a  and subframe five (e.g., 5)  569   f  and DwPTS  571   a - b  may be reserved for downlink transmission. The UpPTS  575   a - b  and the subframe(s) immediately following the special subframe(s)  577   a - b  (e.g., subframe two  569   c  and subframe seven  569   h ) may be reserved for uplink transmission. It should be noted that, in some implementations, special subframes  577  may be considered DL subframes in order to determine a set of DL subframe associations that indicate UCI transmission uplink subframes of a UCI transmission cell. 
     LTE license access with TDD can have the special subframe as well as the normal subframe. The lengths of DwPTS, GP and UpPTS can be configured by using a special subframe configuration. Any one of the following ten configurations may be set as a special subframe configuration. 
     1) Special subframe configuration 0: DwPTS includes 3 OFDM symbols. UpPTS includes 1 single carrier frequency-division multiple access (SC-FDMA) symbol. 
     2) Special subframe configuration 1: DwPTS includes 9 OFDM symbols for normal CP and 8 OFDM symbols for extended CP. UpPTS includes 1 SC-FDMA symbol. 
     3) Special subframe configuration 2: DwPTS includes 10 OFDM symbols for normal CP and 9 OFDM symbols for extended CP. UpPTS includes 1 SC-FDMA symbol. 
     4) Special subframe configuration 3: DwPTS includes 11 OFDM symbols for normal CP and 10 OFDM symbols for extended CP. UpPTS includes 1 SC-FDMA symbol. 
     5) Special subframe configuration 4: DwPTS includes 12 OFDM symbols for normal CP and 3 OFDM symbols for extended CP. UpPTS includes 1 SC-FDMA symbol for normal CP and 2 SC-FDMA symbol for extended CP. 
     6) Special subframe configuration 5: DwPTS includes 3 OFDM symbols for normal CP and 8 OFDM symbols for extended CP. UpPTS includes 2 SC-FDMA symbols. 
     7) Special subframe configuration 6: DwPTS includes 9 OFDM symbols. UpPTS includes 2 SC-FDMA symbols. 
     8) Special subframe configuration 7: DwPTS includes 10 OFDM symbols for normal CP and 5 OFDM symbols for extended CP. UpPTS includes 2 SC-FDMA symbols. 
     9) Special subframe configuration 8: DwPTS includes 11 OFDM symbols. UpPTS includes 2 SC-FDMA symbols. Special subframe configuration 8 can be configured only for normal CP 
     10) Special subframe configuration 9: DwPTS includes 6 OFDM symbols. UpPTS includes 2 SC-FDMA symbols. Special subframe configuration 9 can be configured only for normal CP. 
       FIG. 6  is a diagram illustrating one example of a resource grid for the downlink. The resource grid illustrated in  FIG. 6  may be utilized in some implementations of the systems and methods disclosed herein. More detail regarding the resource grid is given in connection with  FIG. 1 . 
     In  FIG. 6 , one downlink subframe  669  may include two downlink slots  683 . DL DL   RB  is downlink bandwidth configuration of the serving cell, expressed in multiples of N RB   sc , where N RB    sc  is a resource block  687  size in the frequency domain expressed as a number of subcarriers, and N DL   symb  is the number of OFDM symbols  1085  in a downlink slot  683 . A resource block  687  may include a number of resource elements (RE)  689 . 
     For a PCell, N DL   RB  is broadcast as a part of system information. For an SCell (including an LAA SCell), N DL   RB  is configured by a RRC message dedicated to a UE  102 . For PDSCH mapping, the available RE  689  may be the RE  689  whose index 1 fulfills 1≧1 data,start  and/or 1 data,end ≧1 in a subframe. 
       FIG. 7  is a diagram illustrating one example of a resource grid for the uplink. The resource grid illustrated in  FIG. 7  may be utilized in some implementations of the systems and methods disclosed herein. More detail regarding the resource grid is given in connection with  FIG. 1 . 
     In  FIG. 7 , one uplink subframe  769  may include two uplink slots  783 . N UL   RB  is uplink bandwidth configuration of the serving cell, expressed in multiples of N RB   sc , where N RB   sc  is a resource block  789  size in the frequency domain expressed as a number of subcarriers, and N UL   symb  is the number of SC-FDMA symbols  793  in an uplink slot  783 . A resource block  789  may include a number of resource elements (RE)  791 . 
     For a PCell, N UL   RB  is broadcast as a part of system information. For an SCell (including an LAA SCell), N UL   RB  is configured by a RRC message dedicated to a UE  102 . 
       FIG. 8  illustrates an example of a retransmission cycle of a DL transport block (DL-TB). When data transmission occurs in a higher layer at the eNB side, the eNB  860  may determine physical layer parameters (e.g., MCS, PRB assignment, etc.) for an initial transmission of the DL-TB. The eNB  860  may transmit  801  a DL assignment and the corresponding PDSCH carrying the DL-TB(s) in the same subframe. 
     If the UE  802  detects PDCCH or EPDCCH carrying the DL assignment, the UE  802  may attempt to decode DL-TB in the corresponding PDSCH. If the UE  802  succeeds to decode DL-TB, then the UE  802  may report  803  ACK as the HARQ-ACK in the subframe 4-TTI later than the subframe carrying the DL assignment and DL-TB. Otherwise, the UE  802  reports  803  NACK as the HARQ-ACK in that subframe. 
     When the eNB  860  receives NACK, the eNB  860  re-transmits  805  the DL-TB in the subframe 4-TTI later than the subframe carrying HARQ-ACK. Similarly, the next retransmission may be performed in the subframe 8-TTI later than the subframe of the 1st retransmission. Eventually, the retransmission cycle is 8 TTIs. In other words, a given DL-TB may be transmitted in every 8 subframe at minimum as long as the UE  802  reports NACK for the DL-TB. 
     Therefore, from the HARQ-ACK feedback perspective, the HARQ-ACK in subframe n corresponds to PDSCH in subframe n-k (for FDD, k=4 for FDD; for TDD, k is determined depending on UL/DL association set defined for TDD). From the HARQ retransmission perspective, the HARQ RTT timer (i.e., the minimum amount of subframe(s) before a DL HARQ retransmission from the previous transmission) for a HARQ process is set to k+4 such that the UE  802  might not be expected to receive retransmission of the same transport block earlier than subframe n+4. 
     For each serving cell, in case of FDD configuration on the serving cell which carries the HARQ feedback for this serving cell the HARQ RTT timer is set to 8 subframes. For each serving cell, in case of TDD configuration on the serving cell which carries the HARQ feedback for this serving cell the HARQ RTT timer is set to k+4 subframes, where k is the interval between the downlink transmission and the transmission of associated HARQ feedback. Here “n” of “subframe n” expresses a subframe number, which is incremented with “1” subframe by subframe in time domain. 
       FIG. 9  illustrates an example of a retransmission cycle of a UL transport block (UL-TB). When data transmission occurs in a higher layer at the UE side, the UE  902  may send  901  a scheduling request (SR) or may initiate a Random Access Channel (RACH) procedure instead of sending the SR. 
     If the eNB  960  receives the SR or finished the RACH procedure, the eNB  960  may determine physical layer parameters (e.g., MCS, PRB assignment, etc.) for an initial transmission of the UL-TB. The eNB  960  may transmit  903  an UL grant. 
     If the UE  902  detects PDCCH or EPDCCH carrying the UL grant, the UE  902  may transmit  905  PUSCH containing the UL-TB in the subframe 4-TTI later than the subframe carrying the UL grant. The eNB  960  may attempt to decode the UL-TB. 
     If the UE  902  succeeds to decode DL-TB, then the eNB  960  may report  907  ACK as the HARQ-ACK or may send another UL grant scheduling a new UL-TB in the subframe 4-TTI later than the subframe carrying the UL-TB. Otherwise, the eNB  960  may report NACK as the HARQ-ACK or may send another UL grant scheduling the same UL-TB in that subframe. 
     When the UE  902  receives NACK or another UL grant scheduling the same UL-TB, the UE  902  may re-transmit  909  the UL-TB in the subframe 4-TTI later than the subframe carrying HARQ-ACK or the UL grant. Similarly, the next retransmission may be performed in the subframe 8-TTI later than the subframe of the 1st retransmission. Eventually, the retransmission cycle is 8 TTIs. In other words, a given UL-TB may be transmitted in every 8 subframe at minimum as long as the eNB  960  reports NACK or sends an UL grant initiating a retransmission for the UL-TB. 
       FIG. 10  illustrates an example of a retransmission cycle of a DL-TB with a shortened Round Trip Time (RTT) timeline. When data transmission occurs in a higher layer at the eNB side, the eNB  1060  may determine physical layer parameters for an initial transmission of the DL-TB. The eNB  1060  may transmit  1001  a DL assignment and the corresponding PDSCH carrying the DL-TB(s) in the same subframe. 
     If the UE  1002  detects the PDCCH or EPDCCH carrying the DL assignment, the UE  1002  may attempt to decode DL-TB in the corresponding PDSCH. If the UE  1002  succeeds to decode DL-TB, then the UE  1002  may report  1003  ACK as the HARQ-ACK in the subframe 2-TTI later than the subframe carrying the DL assignment and DL-TB. Otherwise, the UE  1002  may report  1003  NACK as the HARQ-ACK in that subframe. 
     When the eNB  1060  receives NACK, the eNB  1060  may re-transmit  1005  the DL-TB in the subframe 2-TTI later than the subframe carrying HARQ-ACK. Similarly, the next retransmission may be performed in the subframe 4-TTI later than the subframe of the 1st retransmission. 
     Eventually, the retransmission cycle is 4 TTIs. In other words, a given DL-TB may be transmitted in every 4 subframe at minimum as long as the UE  1002  reports NACK for the DL-TB. 
       FIG. 11  illustrates an example of a retransmission cycle of a UL-TB with a shortened RTT timeline. When data transmission occurs in a higher layer at the UE side, the UE  1102  may send  1101  a scheduling request (SR) or may initiate a RACH procedure instead of sending SR. 
     If the eNB  1160  receives the SR or finished the RACH procedure, the eNB  1160  may determine physical layer parameters (e.g., MCS, PRB assignment, etc.) for an initial transmission of the UL-TB. The eNB  1160  may transmit  1103  a UL grant. If the UE  1102  detects a PDCCH or EPDCCH carrying the UL grant, the UE  1102  may transmit  1105  PUSCH containing the UL-TB in the subframe 2-TTI later than the subframe carrying the UL grant. The eNB  1160  may attempt to decode the UL-TB. 
     If the eNB  1160  succeeds to decode UL-TB, then the eNB  1160  may report  1107  ACK as the HARQ-ACK or may send another UL grant scheduling a new UL-TB in the subframe 2-TTI later than the subframe carrying the UL-TB. Otherwise, the eNB  1160  may report  1107  NACK as the HARQ-ACK or may send another UL grant scheduling the same UL-TB in that subframe. 
     When the UE  1102  receives NACK or another UL grant scheduling the same UL-TB, the UE  1102  may re-transmit  1109  the UL-TB in the subframe 2-TTI later than the subframe carrying the HARQ-ACK or the UL grant. Similarly, the next retransmission may be performed in the subframe 4-TTI later than the subframe of the 1st retransmission. 
     Eventually, the retransmission cycle is 4 TTIs. In other words, a given UL-TB may be transmitted in every 4 subframe at minimum as long as the eNB  1160  reports NACK or sends a UL grant initiating a retransmission for the UL-TB. 
     The shortened 2-TTI interval provides a RTT of 4 TTIs, with a 2 OFDM symbol TTI, the RTT is 8 symbols. If the interval is 3 TTIs, the RTT is 6 TTIs, with a 2 OFDM symbol TTI, the RTT is 12 symbols. Both of them are under 1 ms RTT. 
       FIG. 12  illustrates various components that may be utilized in a UE  1202 . The UE  1202  described in connection with  FIG. 12  may be implemented in accordance with the UE  102  described in connection with  FIG. 1 . The UE  1202  includes a processor  1203  that controls operation of the UE  1202 . The processor  1203  may also be referred to as a central processing unit (CPU). Memory  1205 , which may include read-only memory (ROM), random access memory (RAM), a combination of the two or any type of device that may store information, provides instructions  1207   a  and data  1209   a  to the processor  1203 . A portion of the memory  1205  may also include non-volatile random access memory (NVRAM). Instructions  1207   b  and data  1209   b  may also reside in the processor  1203 . Instructions  1207   b  and/or data  1209   b  loaded into the processor  1203  may also include instructions  1207   a  and/or data  1209   a  from memory  1205  that were loaded for execution or processing by the processor  1203 . The instructions  1207   b  may be executed by the processor  1203  to implement the method  300  described above. 
     The UE  1202  may also include a housing that contains one or more transmitters  1258  and one or more receivers  1220  to allow transmission and reception of data. The transmitter(s)  1258  and receiver(s)  1220  may be combined into one or more transceivers  1218 . One or more antennas  1222   a - n  are attached to the housing and electrically coupled to the transceiver  1218 . 
     The various components of the UE  1202  are coupled together by a bus system  1211 , which may include a power bus, a control signal bus and a status signal bus, in addition to a data bus. However, for the sake of clarity, the various buses are illustrated in  FIG. 12  as the bus system  1211 . The UE  1202  may also include a digital signal processor (DSP)  1213  for use in processing signals. The UE  1202  may also include a communications interface  1215  that provides user access to the functions of the UE  1202 . The UE  1202  illustrated in  FIG. 12  is a functional block diagram rather than a listing of specific components. 
       FIG. 13  illustrates various components that may be utilized in an eNB  1360 . The eNB  1360  described in connection with  FIG. 13  may be implemented in accordance with the eNB  160  described in connection with  FIG. 1 . The eNB  1360  includes a processor  1303  that controls operation of the eNB  1360 . The processor  1303  may also be referred to as a central processing unit (CPU). Memory  1305 , which may include read-only memory (ROM), random access memory (RAM), a combination of the two or any type of device that may store information, provides instructions  1307   a  and data  1309   a  to the processor  1303 . A portion of the memory  1305  may also include non-volatile random access memory (NVRAM). Instructions  1307   b  and data  1309   b  may also reside in the processor  1303 . Instructions  1307   b  and/or data  1309   b  loaded into the processor  1303  may also include instructions  1307   a  and/or data  1309   a  from memory  1305  that were loaded for execution or processing by the processor  1303 . The instructions  1307   b  may be executed by the processor  1303  to implement the method  400  described above. 
     The eNB  1360  may also include a housing that contains one or more transmitters  1317  and one or more receivers  1378  to allow transmission and reception of data. The transmitter(s)  1317  and receiver(s)  1378  may be combined into one or more transceivers  1376 . One or more antennas  1380   a - n  are attached to the housing and electrically coupled to the transceiver  1376 . 
     The various components of the eNB  1360  are coupled together by a bus system  1311 , which may include a power bus, a control signal bus and a status signal bus, in addition to a data bus. However, for the sake of clarity, the various buses are illustrated in  FIG. 13  as the bus system  1311 . The eNB  1360  may also include a digital signal processor (DSP)  1313  for use in processing signals. The eNB  1360  may also include a communications interface  1315  that provides user access to the functions of the eNB  1360 . The eNB  1360  illustrated in  FIG. 13  is a functional block diagram rather than a listing of specific components. 
       FIG. 14  is a block diagram illustrating one implementation of a UE  1402  in which systems and methods for low latency radio communications may be implemented. The UE  1402  includes transmit means  1458 , receive means  1420  and control means  1424 . The transmit means  1458 , receive means  1420  and control means  1424  may be configured to perform one or more of the functions described in connection with  FIG. 1  above.  FIG. 12  above illustrates one example of a concrete apparatus structure of  FIG. 14 . Other various structures may be implemented to realize one or more of the functions of  FIG. 1 . For example, a DSP may be realized by software. 
       FIG. 15  is a block diagram illustrating one implementation of an eNB  1560  in which systems and methods for low latency radio communications may be implemented. The eNB  1560  includes transmit means  1517 , receive means  1578  and control means  1582 . The transmit means  1517 , receive means  1578  and control means  1582  may be configured to perform one or more of the functions described in connection with  FIG. 1  above.  FIG. 13  above illustrates one example of a concrete apparatus structure of  FIG. 15 . Other various structures may be implemented to realize one or more of the functions of  FIG. 1 . For example, a DSP may be realized by software. 
     The term “computer-readable medium” refers to any available medium that can be accessed by a computer or a processor. The term “computer-readable medium,” as used herein, may denote a computer- and/or processor-readable medium that is non-transitory and tangible. By way of example, and not limitation, a computer-readable or processor-readable medium may comprise RAM, ROM, electrically erasable programmable read-only memory (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 in the form of instructions or data structures and that can be accessed by a computer or processor. Disk and disc, as used herein, includes 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. 
     It should be noted that one or more of the methods described herein may be implemented in and/or performed using hardware. For example, one or more of the methods described herein may be implemented in and/or realized using a chipset, an application-specific integrated circuit (ASIC), a large-scale integrated circuit (LSI) or integrated circuit, etc. 
     Each of the methods disclosed herein comprises one or more steps or actions for achieving the described method. The method steps and/or actions may be interchanged with one another and/or combined into a single step without departing from the scope of the claims. In other words, unless a specific order of steps or actions is required for proper operation of the method that is being described, the order and/or use of specific steps and/or actions may be modified without departing from the scope of the claims. 
     It is to be understood that the claims are not limited to the precise configuration and components illustrated above. Various modifications, changes and variations may be made in the arrangement, operation and details of the systems, methods, and apparatus described herein without departing from the scope of the claims. 
     A program running on the eNB  160  or the UE  102  according to the described systems and methods is a program (a program for causing a computer to operate) that controls a CPU and the like in such a manner as to realize the function according to the described systems and methods. Then, the information that is handled in these apparatuses is temporarily stored in a RAM while being processed. Thereafter, the information is stored in various ROMs or HDDs, and whenever necessary, is read by the CPU to be modified or written. As a recording medium on which the program is stored, among a semiconductor (for example, a ROM, a nonvolatile memory card, and the like), an optical storage medium (for example, a DVD, a MO, a MD, a CD, a BD, and the like), a magnetic storage medium (for example, a magnetic tape, a flexible disk, and the like), and the like, any one may be possible. Furthermore, in some cases, the function according to the described systems and methods described above is realized by running the loaded program, and in addition, the function according to the described systems and methods is realized in conjunction with an operating system or other application programs, based on an instruction from the program. 
     Furthermore, in a case where the programs are available on the market, the program stored on a portable recording medium can be distributed or the program can be transmitted to a server computer that connects through a network such as the Internet. In this case, a storage device in the server computer also is included. Furthermore, some or all of the eNB  160  and the UE  102  according to the systems and methods described above may be realized as an LSI that is a typical integrated circuit. Each functional block of the eNB  160  and the UE  102  may be individually built into a chip, and some or all functional blocks may be integrated into a chip. Furthermore, a technique of the integrated circuit is not limited to the LSI, and an integrated circuit for the functional block may be realized with a dedicated circuit or a general-purpose processor. Furthermore, if with advances in a semiconductor technology, a technology of an integrated circuit that substitutes for the LSI appears, it is also possible to use an integrated circuit to which the technology applies. 
     Moreover, each functional block or various features of the base station device and the terminal device used in each of the aforementioned embodiments may be implemented or executed by a circuitry, which is typically an integrated circuit or a plurality of integrated circuits. The circuitry designed to execute the functions described in the present specification may comprise a general-purpose processor, a digital signal processor (DSP), an application specific or general application integrated circuit (ASIC), a field programmable gate array (FPGA), or other programmable logic devices, discrete gates or transistor logic, or a discrete hardware component, or a combination thereof. The general-purpose processor may be a microprocessor, or alternatively, the processor may be a conventional processor, a controller, a microcontroller or a state machine. The general-purpose processor or each circuit described above may be configured by a digital circuit or may be configured by an analogue circuit. Further, when a technology of making into an integrated circuit superseding integrated circuits at the present time appears due to advancement of a semiconductor technology, the integrated circuit by this technology is also able to be used.