Systems and methods for operating with different transmission time interval (TTI) durations

Abstract

To provide a device and a technique for determining a transmission time interval (TTI) duration and / or varying the TTI duration.SOLUTION: A TTI duration may be varied based on one or more of timing of transmission, the amount of data available for transmission, and a type of data to be transmitted. The TTI duration may be for one or more of an enhanced physical downlink control channel (EPDCCH), a physical downlink shared channel (PDSCH), and / or a physical uplink control channel (PUCCH). One or more different TTI durations may be achieved by modifying the number of OFDM symbols per TTI and / or symbol duration (e.g., subcarrier spacing). One or more variable time-slot boundaries are contemplated. The TTI duration per set of subcarriers is contemplated. One or more timing rules to deal with different processing times are contemplated.SELECTED DRAWING: Figure 6

Description

[Technical Field]

[0001] The present invention relates to wireless communications. [Background technology]

[0002] CROSS-REFERENCE TO RELATED APPLICATIONS This application claims the benefit of U.S. Provisional Patent Application No. 62 / 047,610, filed September 8, 2014, and U.S. Provisional Patent Application No. 62 / 204,380, filed August 12, 2015, the entire disclosures of which are hereby incorporated by reference for all purposes as if fully set forth in their respective entireties.

[0003] Automatic Repeat Request (ARQ) and Hybrid Automatic Repeat Request (HARQ) are techniques that may be used for error checking and / or correction for errors, such as those performed during signal transmission. Latency in wireless networks may be caused by one or more factors, which may include the use of HARQ. Summary of the Invention

[0004] A wireless transmit / receive unit (WTRU) includes a processor programmed to execute instructions stored in a computer memory, including determining a transmission time interval (TTI) duration and / or reducing the TTI duration. The WTRU processor may be programmed to reduce (and / or vary) the TTI duration based on one or more of the timing of the transmission, the amount of data available for transmission, and / or the type of data to be transmitted. The transmission time interval duration may be for one or more of an enhanced physical downlink control channel (EPDCCH), a physical downlink shared channel (PDSCH), and / or a physical uplink control channel (PUCCH).

[0005] The TTI duration may be achieved, for example, by varying one or more of the number of OFDM symbols per TTI and / or the symbol duration (e.g., subcarrier spacing). The RE mapping may be based on the TTI duration. The RE mapping may be dependent on the number of OFDM symbols, for example, the number of OFDM symbols per TTI. One or more variable time slot boundaries are contemplated.

[0006] TTI duration per set of subcarriers is contemplated. One or more (e.g., additional) timing rules are contemplated to accommodate different processing times. One or more (e.g., additional) rules are contemplated to accommodate one or more or multiple simultaneous feedback reports. One or more (e.g., additional) rules are contemplated for UL scheduling with reduced TTI duration.

[0007] A wireless transmit / receive unit (WTRU) may comprise a processor. The processor may be configured to dynamically determine a first transmission time interval (TTI) duration based on one or more factors. The processor may be configured to dynamically determine a second TTI duration based on one or more factors. The second TTI duration may differ from the first TTI duration. The processor may be configured to assign the first TTI duration to a first channel of one or more channels. The processor may be configured to assign the second TTI duration to a second channel of the one or more channels. The WTRU may comprise a transmitter. The transmitter may be configured to send a first transmission over the first channel within the first TTI duration.

[0008] A wireless transmit / receive unit (WTRU) may comprise a processor. The processor may be configured to associate a first transmission time interval (TTI) duration with a first hybrid automatic repeat request (HARQ) process. The processor may be configured to associate a second TTI duration with a second HARQ process. The second TTI duration may differ from the first TTI duration. The WTRU may be configured to activate at least one of the first HARQ process or the second HARQ process. The WTRU may comprise a transmitter. The transmitter may be configured to send a first transmission within at least one of the first TTI duration using the first HARQ process or the second TTI duration using the second HARQ process.

[0009] A wireless transmit / receive unit (WTRU) may include a receiver. The receiver may be configured to receive an enhanced physical downlink control channel (EPDCCH). The WTRU may include a processor. The processor may be configured to identify a first transmission time interval (TTI) duration based at least in part on the EPDCCH. The receiver may be configured to receive a first transmission via a physical downlink shared channel (PDSCH) within the first TTI duration. The WTRU may include a transmitter. The transmitter may be configured to send a second transmission via a physical uplink shared channel (PUSCH) within a second TTI duration. The second TTI duration may be different from the first TTI duration.

[0010] A wireless transmit / receive unit (WTRU) may comprise a receiver. The receiver may be configured to receive an enhanced physical downlink control channel (EPDCCH) configuration. The EPDCCH configuration may include information for one or more EPDCCH search spaces. The WTRU may comprise a processor. The processor may be configured to assign a first transmission time interval (TTI) duration to a first EPDCCH search space of the one or more EPDCCH search spaces. The processor may be configured to assign a second TTI duration to a second EPDCCH search space of the one or more EPDCCH search spaces. The second TTI duration may be different from the first TTI duration. [Brief explanation of the drawings]

[0011] A more detailed understanding may be had from the following description, given by way of example in conjunction with the accompanying drawings, in which: [Figure 1A] FIG. 1 illustrates an example communication system in which one or more disclosed embodiments may be implemented. [Figure 1B] FIG. 1 is a system diagram of an example wireless transmit / receive unit in which one or more disclosed embodiments may be implemented. [Figure 1C] FIG. 1 is a system diagram of a radio access network and a core network in which one or more disclosed embodiments may be implemented. [Figure 1D] FIG. 1 is a system diagram of a radio access network and a core network in which one or more disclosed embodiments may be implemented. [Figure 1E] FIG. 1 is a system diagram of a radio access network and a core network in which one or more disclosed embodiments may be implemented. [Figure 2] FIG. 1 illustrates an example physical layer channel that may be used in one or more embodiments. [Figure 3] FIG. 2 illustrates an example uplink physical layer channel that may be used in one or more embodiments. [Figure 4]A diagram showing examples of different TTI durations in one or more different subframes and / or in one or more different bandwidth portions. [Figure 5] 1 illustrates an example scheduling using a reduced transmission time interval EPDCCH for a reduced transmission time interval PDSCH that may be used in one or more embodiments. [Figure 6] FIG. 1 illustrates an example PUCCH transmitted in a single timeslot using two resource blocks (RBs) and the entire timeslot, which may be used in one or more embodiments. [Figure 7] FIG. 10 illustrates an example PUCCH transmitted in a single timeslot transmitted over half a timeslot and over two RBs, which may be used in one or more embodiments. DETAILED DESCRIPTION OF THE INVENTION

[0012] A detailed description of exemplary embodiments will now be set forth in connection with various figures. While this description provides detailed examples of possible implementations, it should be noted that the details are for illustrative purposes only and are in no way intended to limit the scope of the present application. As used herein, the articles "a" and "an" may be understood to mean, for example, "one or more" or "at least one," unless further stipulated or stated.

[0013] 1A is a diagram of an example communication system 100 in which one or more disclosed embodiments may be implemented. The communication system 100 may be a multiple-access system that provides content, such as voice, data, video, messaging, broadcasts, etc., to multiple wireless users. The communication system 100 may enable the multiple wireless users to access such content through sharing of system resources, including wireless bandwidth. For example, the communication system 100 may use one or more channel access schemes, such as code division multiple access (CDMA), time division multiple access (TDMA), frequency division multiple access (FDMA), orthogonal FDMA (OFDMA), single-carrier FDMA (SC-FDMA), etc.

[0014] 1A, communications system 100 may include wireless transmit / receive units (WTRUs) 102a, 102b, 102c, and / or 102d (which may be collectively or collectively referred to as WTRUs 102), radio access networks (RANs) 103 / 104 / 105, core networks 106 / 107 / 109, public switched telephone network (PSTN) 108, the Internet 110, and other networks 112, although it will be understood that the disclosed embodiments contemplate any number of WTRUs, base stations, networks, and / or network elements. Each of WTRUs 102a, 102b, 102c, 102d may be any type of device configured to operate and / or communicate in a wireless environment. By way of example, WTRUs 102a, 102b, 102c, 102d may be configured to transmit and / or receive wireless signals and may include user equipment (UE), mobile stations, fixed or mobile subscriber units, pagers, mobile phones, personal digital assistants (PDAs), smartphones, laptops, notebooks, personal computers, wireless sensors, consumer electronic devices, etc.

[0015] The communications system 100 may also include a base station 114a and a base station 114b. Each of the base stations 114a, 114b may be any type of device configured to wirelessly interface with at least one of the WTRUs 102a, 102b, 102c, 102d to facilitate access to one or more communications networks, such as the core networks 106 / 107 / 109, the Internet 110, and / or the network 112. By way of example, the base stations 114a, 114b may be a base transceiver station (BTS), a Node B, an eNodeB, a Home Node B, a Home eNodeB, a site controller, an access point (AP), a wireless router, etc. Although the base stations 114a, 114b are each shown as a single element, it will be understood that the base stations 114a, 114b may include any number of interconnected base stations and / or network elements.

[0016] The base station 114a may be part of the RAN 103 / 104 / 105, which may also include other base stations and / or network elements (not shown), such as a base station controller (BSC), a radio network controller (RNC), relay nodes, etc. The base station 114a and / or base station 114b may be configured to transmit and / or receive wireless signals within a particular geographic area, which may be referred to as a cell (not shown). A cell may be further divided into cell sectors. For example, the cell associated with the base station 114a may be divided into three sectors. Thus, in one embodiment, the base station 114a may include three transceivers, one for each sector of the cell. In another embodiment, the base station 114a may use multiple-input multiple-output (MIMO) technology and thus utilize multiple transceivers for each sector of the cell.

[0017] The base stations 114a, 114b may communicate with one or more of the WTRUs 102a, 102b, 102c, 102d over an air interface 115 / 116 / 117, which may be any suitable wireless communication link (e.g., radio frequency (RF), microwave, infrared (IR), ultraviolet (UV), visible light, etc.). The air interface 115 / 116 / 117 may be established using any suitable radio access technology (RAT).

[0018] More specifically, as noted above, the communication system 100 may be a multiple-access system and may use one or more channel access schemes, such as CDMA, TDMA, FDMA, OFDMA, SC-FDMA, etc. For example, the base station 114a and the WTRUs 102a, 102b, 102c in the RANs 103 / 104 / 105 may implement a radio technology such as Universal Mobile Telecommunications System (UMTS) Terrestrial Radio Access (UTRA), which may establish the air interface 115 / 116 / 117 using Wideband CDMA (WCDMA). WCDMA may include communication protocols such as High Speed ​​Packet Access (HSPA) and / or Evolved HSPA (HSPA+). HSPA may include High Speed ​​Downlink Packet Access (HSDPA) and / or High Speed ​​Uplink Packet Access (HSUPA).

[0019] In another embodiment, the base station 114a and the WTRUs 102a, 102b, 102c may implement a radio technology such as Evolved UMTS Terrestrial Radio Access (E-UTRA), which may establish the air interface 115 / 116 / 117 using Long Term Evolution (LTE) and / or LTE-Advanced (LTE-A).

[0020] In other embodiments, the base station 114a and the WTRUs 102a, 102b, 102c may implement a radio technology such as IEEE 802.16 (i.e., Worldwide Interoperability for Microwave Access (WiMAX)), CDMA2000, CDMA2000 1X, CDMA2000 EV-DO, Interim Standard 2000 (IS-2000), Interim Standard 95 (IS-95), Interim Standard 856 (IS-856), Global System for Mobile Communications (GSM), Enhanced Data Rates for GSM Evolution (EDGE), GSM EDGE (GERAN), or the like.

[0021] The base station 114b in FIG. 1A may be, for example, a wireless router, a Home NodeB, a Home eNodeB, or an access point and may utilize any suitable RAT for facilitating wireless connectivity in a local area, such as a business, a home, a vehicle, a campus, etc. In one embodiment, the base station 114b and the WTRUs 102c, 102d may implement a radio technology such as IEEE 802.11 to establish a wireless local area network (WLAN). In another embodiment, the base station 114b and the WTRUs 102c, 102d may implement a radio technology such as IEEE 802.15 to establish a wireless personal area network (WPAN). In another embodiment, the base station 114b and the WTRUs 102c, 102d may utilize a cellular-based RAT (e.g., WCDMA, CDMA2000, GSM, LTE, LTE-A, etc.) to establish a picocell or femtocell. As shown in FIG. 1A, the base station 114b may have a direct connection to the Internet 110. Therefore, the base station 114b may not need to access the Internet 110 via the core network 106 / 107 / 109.

[0022] The RANs 103 / 104 / 105 may communicate with the core network 106 / 107 / 109, which may be any type of network configured to provide voice, data, application, and / or VoIP services to one or more of the WTRUs 102a, 102b, 102c, 102d. For example, the core network 106 / 107 / 109 may provide call control, billing services, mobile location-based services, prepaid calls, Internet connectivity, video distribution, etc., and / or perform high-level security functions such as user authentication. Although not shown in FIG. 1A , it will be understood that the RANs 103 / 104 / 105 and / or the core network 106 / 107 / 109 may communicate, directly or indirectly, with other RANs that use the same RAT as the RANs 103 / 104 / 105 or a different RAT. For example, in addition to being connected to RANs 103 / 104 / 105 that may utilize E-UTRA radio technology, core networks 106 / 107 / 109 may also communicate with another RAN (not shown) that uses GSM radio technology.

[0023] The core networks 106 / 107 / 109 can also serve as gateways for the WTRUs 102a, 102b, 102c, 102d to access the PSTN 108, the Internet 110, and / or other networks 112. The PSTN 108 can include a circuit-switched telephone network that provides plain old telephone service (POTS). The Internet 110 can include a global system of interconnected computer networks and devices that use common communication protocols, such as TCP, UDP, and IP in the TCP / IP Internet protocol suite. The network 112 can include wired or wireless communication networks owned and / or operated by other service providers. For example, the network 112 can include another core network connected to one or more RANs, which can use the same RAT as the RANs 103 / 104 / 105 or a different RAT.

[0024] Some or all of the WTRUs 102a, 102b, 102c, 102d in the communications system 100 may include multi-mode capabilities, i.e., the WTRUs 102a, 102b, 102c, 102d may include multiple transceivers for communicating with different wireless networks over different wireless links. For example, the WTRU 102c shown in FIG. 1A may be configured to communicate with a base station 114a, which may use a cellular-based wireless technology, and with a base station 114b, which may use an IEEE 802.11 wireless technology.

[0025] 1B is a system diagram of an example WTRU 102. As shown in FIG. 1B, the WTRU 102 may include a processor 118, a transceiver 120, a transmit / receive element 122, a speaker / microphone 124, a keypad 126, a display / touchpad 128, non-removable memory 130, removable memory 132, a power source 134, a GPS chipset 136, and other peripherals 138. It will be understood that the WTRU 102 may include any subcombination of the above elements while remaining consistent with an embodiment. Embodiments also contemplate that the base stations 114a and 114b, and / or the nodes they may represent, such as, but not limited to, a transceiver station (BTS), a Node B, a site controller, an access point (AP), a Home Node B, an evolved Home Node B (eNodeB), a Home Evolved Node B (HeNB), a Home Evolved Node B Gateway, and a proxy node, among others, may include some or all of the elements shown in FIG. 1B and described herein.

[0026] The processor 118 may be a general-purpose processor, a special-purpose processor, a conventional processor, a digital signal processor (DSP), multiple microprocessors, one or more microprocessors associated with a DSP core, a controller, a microcontroller, an application specific integrated circuit (ASIC), a field programmable gate array (FPGA) circuit, any other type of integrated circuit (IC), a state machine, etc. The processor 118 may perform signal coding, data processing, power control, input / output processing, and / or any other function that enables the WTRU 102 to operate in a wireless environment. The processor 118 may be coupled to the transceiver 120, which may be coupled to the transmit / receive element 122. While FIG. 1B depicts the processor 118 and the transceiver 120 as separate components, it will be understood that the processor 118 and the transceiver 120 may be integrated together in an electronic circuit package or chip.

[0027] The transmit / receive element 122 may be configured to transmit signals to or receive signals from a base station (e.g., base station 114a) over the air interface 115 / 116 / 117. For example, in one embodiment, the transmit / receive element 122 may be an antenna configured to transmit and / or receive RF signals. In another embodiment, the transmit / receive element 122 may be an emitter / detector configured to transmit and / or receive IR, UV, or visible light signals, for example. In another embodiment, the transmit / receive element 122 may be configured to transmit and / or receive both RF and light signals. It will be understood that the transmit / receive element 122 may be configured to transmit and / or receive any combination of wireless signals.

[0028] 1B shows the transmit / receive element 122 as a single element, the WTRU 102 may include any number of transmit / receive elements 122. More specifically, the WTRU 102 may use MIMO technology. Thus, in one embodiment, the WTRU 102 may include two or more transmit / receive elements 122 (e.g., multiple antennas) for transmitting and receiving wireless signals over the air interface 115 / 116 / 117.

[0029] The transceiver 120 may be configured to modulate signals to be transmitted by the transmit / receive element 122 and to demodulate signals received by the transmit / receive element 122. As mentioned above, the WTRU 102 may have multi-mode capabilities. Thus, the transceiver 120 may include multiple transceivers to enable the WTRU 102 to communicate over multiple RATs, such as UTRA and IEEE 802.11.

[0030] The processor 118 of the WTRU 102 may be coupled to and may receive user input data from a speaker / microphone 124, a keypad 126, and / or a display / touchpad 128 (e.g., a liquid crystal display (LCD) display unit or an organic light emitting diode (OLED) display unit). The processor 118 may also output user data to the speaker / microphone 124, the keypad 126, and / or the display / touchpad 128. Further, the processor 118 may access information from and store data in any type of suitable memory, such as non-removable memory 130 and / or removable memory 132. The non-removable memory 130 may include RAM, ROM, a hard disk, or any other type of memory storage device. The removable memory 132 may include a subscriber identity module (SIM) card, a memory stick, a secure digital (SD) memory card, etc. In other embodiments, the processor 118 may access information from and store data in memory that is not physically located on the WTRU 102, such as on a server or home computer (not shown).

[0031] The processor 118 may receive power from the power source 134 and may be configured to distribute and / or control the power to other components within the WTRU 102. The power source 134 may be any suitable device for powering the WTRU 102. For example, the power source 134 may include one or more dry batteries (e.g., nickel-cadmium (NiCd), nickel-zinc (NiZn), nickel-metal hydride (NiMH), lithium-ion (Li-ion), etc.), solar cells, fuel cells, etc.

[0032] The processor 118 may also be coupled to a GPS chipset 136, which may be configured to provide location information (e.g., longitude and latitude) regarding the current location of the WTRU 102. In addition to or instead of information from the GPS chipset 136, the WTRU 102 may receive location information from a base station (e.g., base stations 114a, 114b) over the air interface 115 / 116 / 117 and / or may determine its location based on the timing of signals received from two or more nearby base stations. It will be appreciated that the WTRU 102 may obtain location information by way of any suitable location determination method while remaining consistent with an embodiment.

[0033] The processor 118 may further be coupled to other peripherals 138, which may include one or more software and / or hardware modules that provide additional features, functionality, and / or wired or wireless connectivity. For example, the peripherals 138 may include an accelerometer, an electronic compass, a satellite transceiver, a digital camera (for photos or videos), a USB port, a vibration device, a television receiver / transmitter, a hands-free headset, a Bluetooth module, a frequency modulation (FM) radio unit, a digital music player, a media player, a video game player module, an internet browser, etc.

[0034] 1C is a system diagram of the RAN 103 and the core network 106 according to an embodiment. As described above, the RAN 103 may communicate with the WTRUs 102a, 102b, and 102c over the air interface 115 using UTRA radio technology. The RAN 103 may also communicate with the core network 106. As shown in FIG. 1C, the RAN 103 may include Node Bs 140a, 140b, and 140c, each of which may include one or more transceivers for communicating with the WTRUs 102a, 102b, and 102c over the air interface 115. Each of the Node Bs 140a, 140b, and 140c may be associated with a particular cell (not shown) within the RAN 103. The RAN 103 may also include RNCs 142a and 142b. It will be understood that the RAN 103 may include any number of Node Bs and RNCs while remaining consistent with an embodiment.

[0035] As shown in FIG. 1C , Node Bs 140a and 140b can communicate with RNC 142a. Node B 140c can also communicate with RNC 142b. Node Bs 140a, 140b, and 140c can communicate with RNCs 142a and 142b, respectively, via an Iub interface. RNCs 142a and 142b can also communicate with each other via an Iur interface. Each of RNCs 142a and 142b can be configured to control the respective Node Bs 140a, 140b, and 140c to which it is connected. Each of RNCs 142a and 142b can also be configured to perform or support other functions, such as outer loop power control, load control, admission control, packet scheduling, handover control, macro diversity, security functions, and data encryption.

[0036] 1C may include a media gateway (MGW) 144, a mobile switching center (MSC) 146, a serving GPRS support node (SGSN) 148, and / or a gateway GPRS support node (GGSN) 150. Although each of the above elements is shown as part of the core network 106, it will be understood that any one of these elements may be owned and / or operated by an entity other than the core network operator.

[0037] The RNC 142a in the RAN 103 may be connected to an MSC 146 in the core network 106 via an IuCS interface. The MSC 146 may be connected to an MGW 144. The MSC 146 and MGW 144 may provide the WTRUs 102a, 102b, 102c with access to circuit-switched networks, such as the PSTN 108, to facilitate communications between the WTRUs 102a, 102b, 102c and traditional landline communication devices.

[0038] The RNC 142a in the RAN 103 may also be connected to an SGSN 148 in the core network 106 via an IuPS interface. The SGSN 148 may be connected to a GGSN 150. The SGSN 148 and GGSN 150 may provide the WTRUs 102a, 102b, 102c with access to packet-switched networks, such as the Internet 110, to facilitate communications between the WTRUs 102a, 102b, 102c and IP-enabled devices.

[0039] As mentioned above, the core network 106 may also be connected to the networks 112, which may include other wired or wireless networks owned and / or operated by other service providers.

[0040] 1D is a system diagram of the RAN 104 and the core network 107 according to an embodiment. As mentioned above, the RAN 104 can communicate with the WTRUs 102a, 102b, 102c over the air interface 116 using E-UTRA radio technology. The RAN 104 can also communicate with the core network 107.

[0041] The RAN 104 may include eNodeBs 160a, 160b, and 160c, although it will be understood that the RAN 104 may include any number of eNodeBs while remaining consistent with an embodiment. The eNodeBs 160a, 160b, and 160c may each include one or more transceivers for communicating with the WTRUs 102a, 102b, and 102c over the air interface 116. In one embodiment, the eNodeBs 160a, 160b, and 160c may implement MIMO techniques. Thus, for example, the eNodeB 160a may transmit wireless signals to, and receive wireless signals from, the WTRU 102a using multiple antennas.

[0042] Each of the eNodeBs 160a, 160b, 160c may be associated with a particular cell (not shown) and may be configured to handle radio resource management decisions, handover decisions, scheduling of users on the uplink and / or downlink, etc. As shown in FIG. 1D, the eNodeBs 160a, 160b, 160c may communicate with one another over an X2 interface.

[0043] The core network 107 shown in Figure 1D may include a mobility management entity (MME) 162, a serving gateway 164, and a packet data network (PDN) gateway 166. Although each of the above elements is shown as part of the core network 107, it will be understood that any one of these elements may be owned and / or operated by an entity other than the core network operator.

[0044] The MME 162 may be connected to each of the eNodeBs 160a, 160b, 160c in the RAN 104 via an S1 interface and may act as a control node. For example, the MME 162 may be responsible for authenticating users of the WTRUs 102a, 102b, 102c, bearer activation / deactivation, selecting a particular serving gateway upon initial attach of the WTRUs 102a, 102b, 102c, etc. The MME 162 may also provide a control plane function for switching between the RAN 104 and other RANs (not shown) that employ other radio technologies, such as GSM or WCDMA.

[0045] The serving gateway 164 may be connected to each of the eNodeBs 160a, 160b, 160c in the RAN 104 via an S1 interface. The serving gateway 164 may generally route and forward user data packets to and from the WTRUs 102a, 102b, 102c. The serving gateway 164 may also perform other functions such as anchoring the user plane during inter-eNodeB handovers, triggering paging when downlink data for the WTRUs 102a, 102b, 102c is available, and managing and storing the context of the WTRUs 102a, 102b, 102c.

[0046] The serving gateway 164 may also be connected to a PDN gateway 166 that may provide the WTRUs 102a, 102b, 102c with access to packet-switched networks, such as the Internet 110, to facilitate communications between the WTRUs 102a, 102b, 102c and IP-enabled devices.

[0047] The core network 107 may facilitate communication with other networks. For example, the core network 107 may provide the WTRUs 102a, 102b, 102c with access to circuit-switched networks, such as the PSTN 108, to facilitate communication between the WTRUs 102a, 102b, 102c and traditional land-line communication devices. For example, the core network 107 may include or communicate with an IP gateway (e.g., an IP Multimedia Subsystem (IMS) server) that acts as an interface between the core network 107 and the PSTN 108. Additionally, the core network 107 may provide the WTRUs 102a, 102b, 102c with access to the network 112, which may include other wired or wireless networks owned and / or operated by other service providers.

[0048] 1E is a system diagram of the RAN 105 and the core network 109 according to an embodiment. The RAN 105 may be an access service network (ASN) that communicates with the WTRUs 102a, 102b, 102c over an air interface 117 using IEEE 802.16 wireless technology. As discussed further below, communication links between different functional entities of the WTRUs 102a, 102b, 102c, the RAN 105, and the core network 109 may be defined as reference points.

[0049] As shown in FIG. 1E, the RAN 105 may include base stations 180a, 180b, and 180c and an ASN gateway 182; however, it will be understood that the RAN 105 may include any number of base stations and ASN gateways while remaining consistent with an embodiment. Each of the base stations 180a, 180b, and 180c may be associated with a particular cell (not shown) within the RAN 105 and may include one or more transceivers for communicating with the WTRUs 102a, 102b, and 102c over the air interface 117. In one embodiment, the base stations 180a, 180b, and 180c may implement MIMO technology. Thus, for example, the base station 180a may transmit wireless signals to and receive wireless signals from the WTRU 102a using multiple antennas. The base stations 180a, 180b, and 180c may also provide mobility management functions, such as handoff triggering, tunnel establishment, radio resource management, traffic classification, and quality of service (QoS) policy enforcement. The ASN gateway 182 may act as a traffic aggregation point and may be responsible for paging, caching of subscriber profiles, routing to the core network 109, etc.

[0050] The air interface 117 between the WTRUs 102a, 102b, 102c and the RAN 105 may be defined as an R1 reference point that implements the IEEE 802.16 specification. Additionally, each of the WTRUs 102a, 102b, 102c may establish a logical interface (not shown) with the core network 109. The logical interface between the WTRUs 102a, 102b, 102c and the core network 109 may be defined as an R2 reference point, which may be used for authentication, authorization, IP host configuration management, and / or mobility management.

[0051] The communication link between each of the base stations 180a, 180b, 180c may be defined as an R8 reference point that includes protocols for facilitating WTRU handovers and the transfer of data between the base stations. The communication link between the base stations 180a, 180b, 180c and the ASN gateway 182 may be defined as an R6 reference point that includes protocols for facilitating mobility management based on mobility events associated with each of the WTRUs 102a, 102b, 102c.

[0052] As shown in FIG. 1E, the RAN 105 may be connected to a core network 109. The communication link between the RAN 105 and the core network 109 may be defined as an R3 reference point, including protocols for facilitating, for example, data transfer and mobility management capabilities. The core network 109 may include a Mobile IP Home Agent (MIP-HA) 184, an Authentication, Authorization, and Accounting (AAA) server 186, and a gateway 188. While each of the above elements is shown as part of the core network 109, it will be understood that any one of these elements may be owned and / or operated by an entity other than the core network operator.

[0053] The MIP-HA may be responsible for IP address management and may enable the WTRUs 102a, 102b, 102c to roam between different ASNs and / or different core networks. The MIP-HA 184 may provide the WTRUs 102a, 102b, 102c with access to packet-switched networks, such as the Internet 110, to facilitate communications between the WTRUs 102a, 102b, 102c and IP-enabled devices. The AAA server 186 may be responsible for user authentication and for supporting user services. The gateway 188 facilitates interworking with other networks. For example, the gateway 188 may provide the WTRUs 102a, 102b, 102c with access to circuit-switched networks, such as the PSTN 108, to facilitate communications between the WTRUs 102a, 102b, 102c and traditional landline communications devices. Additionally, the gateway 188 may provide the WTRUs 102a, 102b, 102c with access to the network 112, which may include other wired or wireless networks owned and / or operated by other service providers.

[0054] 1E, it will be understood that the RAN 105 may be connected to other ASNs and the core network 109 may be connected to other core networks. The communication link between the RAN 105 and the other ASNs may be defined as an R4 reference point, which may include protocols for coordinating mobility of the WTRUs 102a, 102b, 102c between the RAN 105 and the other ASNs. The communication link between the core network 109 and the other core networks may be defined as an R5 reference point, which may include protocols for facilitating interoperation between a home core network and a visited core network.

[0055] Embodiments recognize one or more components of latency. After a device has gained access to the resources of a communication system, the latency associated with transmitting useful data may include the addition of one or more of the following components: - the time for transmitting a transport block, e.g., a transmission time interval (TTI), and / or - Processing time at the receiver (e.g., for decoding the transmission), which can be tied to implementation complexity and / or can be the main reason for using fixed timing relationships between one or more different events related to the transmission of one data unit. This can include, for example, fixing timing relationships in scenarios where time division duplexing (TDD) may be used for the carriers of interest and / or synchronous HARQ operation (e.g., for LTE in the uplink).

[0056] In scenarios where the transmission may not be successfully decoded, among other scenarios, one or more of the following factors may apply: - sending feedback, e.g., HARQ ACK or NACK; - Processing time at the receiver, and / or - One or more retransmissions (eg, using steps similar to those above).

[0057] One or more, or each, of the components described herein may be measured at integer multiples of a basic time interval (BTI), for example, in LTE, one or more, or each, of the components described herein may be measured at a TTI.

[0058] Latency in wireless networks can be caused by one or more, or multiple factors. At lower layers, latency can be affected by the need for reliable transmission, which can be achieved by using hybrid automatic repeat request (HARQ). Given that retransmissions may not occur within a contiguous period, one or more retransmissions can affect the latency of a transmission. For downlink transmissions, some processing time at the user equipment (UE) or WTRU can be useful to determine whether the transmission was decoded correctly. This can lead to a time interval between receiving a downlink transmission and / or transmitting an acknowledgement (ACK) or negative acknowledgement (NACK) message. Some processing time at the evolved Node B (eNB) can be useful to determine whether an ACK or NACK was sent by the WTRU or UE and / or whether a retransmission can be useful. A similar situation can arise for uplink (UL) transmissions. Processing time can be cumulative. A trade-off between latency and implementation complexity can be useful.

[0059] A timing relationship between the first transmission for a transport block and its corresponding ACK-NACK HARQ response for the downlink (DL) and / or uplink (UL) directions may be specified in LTE, perhaps to accommodate processing time, among other scenarios. A timing relationship between the first transmission and a retransmission for the UL (e.g., UL only) may be specified in LTE. Time division duplex (TDD) and frequency division duplex (FDD) DL scheduling timing may be the same. For example, a WTRU may receive a scheduling grant for a downlink (DL) transmission in the same subframe and / or transmission time interval (TTI).

[0060] For uplink (UL) transmissions in an FDD system, detection of an (E)PDCCH or (enhanced) physical downlink control channel, and / or a physical hybrid ARQ indicator channel (PHICH) transmission on the uplink with a UL DCI or downlink control information format in subframe n, which may be for the WTRU, may occur. The WTRU may transmit a corresponding physical uplink shared channel (PUSCH) in subframe n+4. For UL transmissions in a TDD system, detection of an (E)PDCCH and / or PHICH transmission with a UL DCI format in subframe n, which may be for the WTRU, may occur. The WTRU may transmit the corresponding PUSCH in subframe n+k. The value of k may depend on one or more of the following: the TDD UL / DL configuration, the subframe in which the UL DCI and / or PHICH was transmitted, the TDD UL / DL configuration 0, the PHICH resource, and / or the most significant bit (MSB) or least significant bit (LSB) of the UL index in the (E)PDCCH.

[0061] For FDD, a HARQ ACK / NACK response for a DL or UL transmission in subframe n may be provided in subframe n+4. For TDD, a HARQ ACK / NACK response for a DL or UL transmission in subframe n may be provided in subframe n+k, where k may depend, for example, on the value of n and / or the TDD UL / DL configuration. For TDD, bundling may be used, for example, to provide HARQ for one or more, or multiple, transmissions.

[0062] The processing time available to the WTRU may depend on the value of the timing advance, which may depend on the distance between the WTRU and the eNB. An example scenario for LTE may be a distance of 100 km, which may correspond to a maximum timing advance of 0.67 ms. There may be approximately 2.3 ms remaining for terminal processing. The processing time available to the eNB may be 3 ms, which may be similar to that of the terminal.

[0063] Physical layer channel locations may be provided. In the DL, there may be three (or more, or fewer) channel areas in a subframe to support the DL-SCH and UL-SCH: a Physical Downlink Control Channel (PDCCH) (which may include a Physical Control Format Indicator Channel (PCFICH) and a Physical Hybrid ARQ Indicator Channel (PHICH)), a Physical Downlink Shared Channel (PDSCH), and / or an EPDCCH (e.g., the PDCCH region, PDSCH region, and EPDCCH are shown in FIG. 2). The EPDCCH may include scheduling information for the WTRU and / or take advantage of the PDSCH region, which may include improving beamforming gain, frequency domain ICIC, and / or PDCCH capacity.

[0064] In the UL, two (or more or fewer) channel areas in a subframe can support DL-SCH and UL-SCH: PUSCH, and / or PDSCH, as shown in Figure 3. One or both of these channels may be transmitted in one or more, or different RBs in each time slot (e.g., frequency hopping of PUSCH), perhaps to improve robustness in frequency-selective channels, for example.

[0065] It may be beneficial to reduce and / or vary the TWI durations of different channels, such as the physical layer channels mentioned herein, perhaps to improve latency, among other reasons. This may allow for a reduction in WTRU processing time and / or the ability for the WTRU to begin processing data sooner. This may allow for a shorter HARQ timeline. Different channels may have different TTI durations. Subframe EPDCCH, PDSCH, PUCCH, and / or PDSCH TTI durations may be shorter. Embodiments may enable efficient HARQ feedback for PDSCH and / or PUSCH transmissions, perhaps using shorter subframe TTI durations. One or more techniques are contemplated for reducing one or more of the latency factors described herein.

[0066] The TTI duration may be defined by the number of OFDM (Orthogonal Frequency Division Multiplexing) symbols. For example, the TTI duration may be defined as an entire subframe or a pair of resource blocks (PRBs, i.e., physical resource blocks) (e.g., 14 OFDM symbols for normal cyclic prefix and 12 OFDM symbols for extended cyclic prefix). The TTI may be as short as a single OFDM symbol. The TTI duration may be defined as one or more time slots (e.g., 7 OFDM symbols for normal cyclic prefix and 6 OFDM symbols for extended cyclic prefix). Combinations of the above TTI durations may be used.

[0067] In one or more techniques, one or more, or all, possible TTI durations may have a fixed number of symbols (e.g., 14 symbols). The symbol time (e.g., duration) may be variable. This may be achieved by changing the subcarrier spacing. For example, a first TTI duration may be achieved by a first subcarrier spacing, and / or a second TTI duration may be achieved by a second subcarrier spacing. Different bandwidth portions (e.g., PRBs) of a carrier may support one or more different subcarrier spacings. This may allow one or more different TTI durations for different bandwidth portions (e.g., PRBs).

[0068] Hybrid techniques may also be used to achieve variable TTI durations (eg, by using different numbers of symbols and / or different symbol durations).

[0069] The subcarrier spacing per bandwidth portion (and / or per carrier) can be static. The subcarrier spacing per portion (and / or per carrier) can be indicated in a broadcast signal (e.g., MIB and / or SIB). The subcarrier spacing can be implicitly determined from the presence of certain types and / or characteristics of synchronization channels and / or reference signals. For example, a first CRS configuration can be present in a first set of PRBs having a first TTI duration, and / or a second CRS configuration can be present in a second set of PRBs having a second TTI duration.

[0070] The subcarrier spacing may be indicated to the WTRU semi-statically, for example, by RRC signaling. The WTRU may receive an indication for new (e.g., new, updated, and / or previously undefined) subcarrier spacing (e.g., possibly one per bandwidth portion), which may be applicable, for example, until a future semi-static indication, among other scenarios. The subcarrier spacing may be tied to a transmission profile.

[0071] The subcarrier spacing may be dynamically indicated to the WTRU. For example, an explicit indication of the subcarrier spacing (e.g., per PRB as the case may be) may be included in the scheduling assignment and / or scheduling grant. The subcarrier spacing may be implicitly determined by the WTRU from parameters of the scheduling assignment or grant.

[0072] As described herein, any technique for operating on and / or displaying TTI duration may be reused as a method for operating on and / or displaying subcarrier spacing.

[0073] The WTRU may determine that it can operate with a particular TTI duration (e.g., subframe TTI duration, timeslot TTI duration). The WTRU may be configured to operate with fixed but different TTI duration configurations in the downlink and uplink. The WTRU may be configured to use the same TTI duration configuration in the downlink and uplink for applicable transmissions.

[0074] WTRU-specific TTI duration: There may be a single duration for a given period. The WTRU may be configured to operate according to one or more TTI durations, which may be for (e.g., only for) a particular period (e.g., based on L3 reconfiguration). The TTI duration may be fixed (e.g., statically, semi-statically, and / or dynamically) for transmissions to and / or from the WTRU (e.g., one or more, or each transmission to and / or from the WTRU).

[0075] One or more, or multiple TTI durations may be configured (e.g., configured in parallel). The WTRU may be configured to operate (e.g., in parallel) for transmissions of different TTI lengths, which may be based on semi-static allocation (e.g., configuration of subsets of frames / subframes dedicated to different TTI lengths based on semi-persistent grants and / or assignments) and / or dynamic allocation (e.g., based on detection and / or reception of downlink control signaling).

[0076] There may be cell / CG-specific TTI durations. Such configurations may be applicable per cell of a WTRU's configuration, for example, for a subset of cells of the WTRU's configuration, for cells of the same Timing Advance Group (TAG) (e.g., all cells) and / or for cells of the same Cell Group (CG) (e.g., all cells). HARQ instances associated with a particular MAC entity may be configured with the same TTI duration. Cells (e.g., all cells) associated with the same channel for uplink control signaling (e.g., PUCCH, PUSCH) may use the same configuration for TTI duration.

[0077] There may be different channels / signals that may have different TTI durations. There may be dedicated resources versus shared resources. The TTI duration configuration may be applicable for (e.g., for transmissions only) transmissions associated with dedicated (e.g., WTRU-specific) resource allocations. For example, preamble (re)transmissions on cell-specific Physical Random Access Channel (PRACH) resources may use legacy TTI durations. HARQ processes for msg3 associated with contention-based random access procedures may use legacy TTI durations. Contention-free preamble transmissions may use the configured TTI durations.

[0078] There may be channel / signal-specific TTI durations. Different channels and signals, e.g., simultaneously, may have different TTI durations. For example, a PDSCH may be separated into one or more, or multiple types depending on the logical channel it serves. For example, a PDSCH used for S1 may use a subframe TTI duration, and a PDSCH used for dedicated traffic may use an RB timeslot TTI duration. Channels associated with DL-SCH (e.g., one or more, or all channels) may use a first TTI duration. Channels associated with UL-SCH (e.g., one or more, or all channels) may use a second TTI duration.

[0079] (E) The PDCCH may have a different TTI duration than the PDSCH. For example, the EPDCCH may be of subframe TTI duration, while the PDSCH may be of timeslot TTI duration. The PDCCH for a timeslot duration may be located in the first {1, 2, 3, 4} OFDM symbols of the timeslot.

[0080] The TTI duration for a channel and / or signal may change dynamically, e.g., based on one or more factors, conditions, capabilities, features, information, and / or data, etc. One or more, or each, channel and / or signal may be allocated a particular TTI duration, perhaps based on one or more of the following: The TTI duration may be based on a semi-static configuration (e.g., by RRC). For example, a WTRU may be configured with a particular TTI length depending on one or more features of its configuration (e.g., the TTI duration may be used for one or more cells of its configuration). For example, a WTRU may be configured with a timeslot TTI duration for (e.g., at least some) secondary cell group (SCG) transmissions, perhaps when configured with dual connectivity, among other scenarios.

[0081] The TTI duration may be based on the timing of the transmission (e.g., frame or subframe number). The TTI duration may be based on the logical channels multiplexed into the transport block. The TTI duration may be based on the logical channels of data available for transmission. For example, the WTRU may initiate a scheduling request (SR) transmission over a physical uplink control channel (PUCCH) with a shorter (e.g., timeslot) TTI duration, e.g., data for a configured first subset of one or more logical channels may be available for transmission. The WTRU may initiate an SR transmission over a PUCCH with a regular (e.g., subframe) TTI duration, e.g., data for a configured second subset of one or more logical channels (e.g., all logical channels not in the first subset of logical channels) may be available for transmission. The TTI duration may be based on the amount of data available for transmission. For example, the WTRU may determine that the physical uplink shared channel (PUSCH) is transmitted over a short (e.g., 1 slot) TTI duration, where, e.g., the amount of data is less than a certain fraction of a transport block size, which may be determined by a grant for a regular (e.g., 1 subframe) TTI duration. The TTI duration can be based on the type of uplink control information (UCI) to be transmitted. For example, channel state information (CSI) can be transmitted through a PUCCH (or PUSCH) of regular (subframe) TTI duration, and HARQ A / N can be transmitted through a PUCCH of shorter (slot) TTI duration or through a single-slot resource element in a PUSCH transmission.

[0082] The TTI duration can be based on the transmission and / or retransmission (e.g., NDI) and / or redundancy version. For example, a transmission can use a first TTI duration. A retransmission can use a second TTI duration. This may enable the ability to transmit one or more, or multiple, redundancy versions with a single retransmission. The TTI duration for a retransmission can be based on the TTI duration of the initial transmission. For example, retransmissions (e.g., all retransmissions) can use the same TTI duration as the initial transmission. The TTI duration can be based on the transport block size. For example, the TTI can be a first duration (e.g., a time slot) in scenarios where the transport block size is smaller than a threshold, and / or a second value in scenarios where the transport block size is larger than a threshold. The TTI duration can also be based on the rank (e.g., number of transmission layers), the number of transport blocks to be transmitted, path loss and / or serving cell RSRP measurements, and / or dynamic signaling. For example, for a path loss measurement, among other scenarios, the WTRU may initiate a PRACH transmission of a first duration and / or associated with a first TTI duration, perhaps if, for example, the path loss is less than a threshold, and / or may initiate a PRACH transmission of a second duration and / or associated with a second TTI duration, perhaps if, for example, the path loss is higher than a threshold.

[0083] One or more, or each, channel and / or signal may be assigned a specific TTI duration based on one or more of the following, such as resource blocks and / or subbands: For example, the center six RBs may use a first TTI duration; other RBs may use a second TTI duration. In such scenarios, among others, to ensure synchronization between TTIs, perhaps at least at some TTI boundaries, the value of the shorter TTI duration may be a submultiple of the duration of the longer TTI. For example, the TTI duration of the center six RBs may be 1 ms, and the TTI duration for perhaps one or more, or all, other RBs may be 0.5 ms. This may ensure that one or more, or any, second, shortened TTIs may be aligned with the boundaries of the longer TTI.

[0084] One or more, or each, channels and / or signals may be allocated a particular TTI duration based on one or more of the following, such as subcarrier spacing: The TTI duration, perhaps measured in number of symbols and / or in time, may depend on the subcarrier spacing of the bandwidth portion in which the channel may be located and / or transmission may occur.

[0085] One or more, or each, channel and / or signal may be allocated a particular TTI duration based on one or more of the following, such as the presence of a reference signal and / or its parameters. For example, the presence of a legacy DM-RS may indicate a first TTI duration, while perhaps the presence of a new (e.g., new, updated, and / or previously undefined) and / or enhanced DM-RS may indicate a second TTI duration. The enhanced DM-RS may reuse legacy DM-RS parameters and / or may differ from the legacy DM-RS by a new (e.g., new, updated, and / or previously undefined) RE position within the TTI.

[0086] One or more, or each, channel and / or signal may be allocated a specific TTI duration based on one or more of the following, such as the presence of one or more specific channels and / or parameters thereof: For example, the TTI duration may be tied to the presence or absence of a control channel; For example, the TTI duration may be tied to a parameter of the control channel (e.g., the number of OFDM symbols for the PDCCH).

[0087] The TTI duration may be based on dynamic signaling. One or more of the following may apply:

[0088] The WTRU may perform blind detection to determine the TTI duration of the channel (e.g., the WTRU monitors a search space for different TTI durations of the (E)PDCCH). The WTRU may dynamically determine the length of the TTI as a function of one or more of the following: the RNTI used for successful blind decoding of the DCI, the search space in which the WTRU decoded the DCI, the aggregation level of the DCI, the first control channel element or CCE of the DCI, and / or the first symbol associated with decoding the DCI. When the WTRU successfully decodes a DCI in a UE-specific search space (UESS) configured for a DCI related to a given TTI duration, the second UESS may indicate a second TTI duration. The WTRU may determine that a DCI decoded in the common search space indicates a transmission of a first (e.g., subframe) TTI duration, while a DCI decoded in the UESS indicates a transmission of a second (e.g., timeslot) duration. The WTRU may determine that the DCI decoded by the first RNTI may be for transmission according to the first TTI duration, while the DCI decoded by the second DCI may be for transmission according to the second TTI duration.

[0089] The TTI duration of the scheduled and / or granted resources may be indicated (e.g., dynamically) in the (E)PDCCH. For example, it may be indicated by a grant and / or allocation (e.g., dynamically scheduled and / or configured) in a DCI received on the (E)PDCCH. For example, it may be indicated by a DCI received in the RAR (e.g., when the WTRU performs contention-free random access (CFRA) and / or when the preamble used for the RACH procedure cannot be selected by the MAC).

[0090] The TTI duration of the expected feedback (eg, PUCCH for HARQ ACK / NACK) may be signaled in the original transmission grant and / or assignment.

[0091] The TTI duration of the expected feedback (eg, PUCCH for HARQ ACK / NACK) may be determined by the TTI duration of the associated transmission.

[0092] The TTI duration for at least RACH message 3 may be indicated in the RACH response message indication. The WTRU may determine the TTI duration as dependent on the RAR reception windows within which the RAR is received. Different windows may correspond to different TTI durations. For example, if the WTRU receives the RAR within a window corresponding to X ms immediately after the last transmission of the preamble, it may determine that the transmission (e.g., the RAR itself and / or a transmission related to a grant in the RAR) is of a first TTI duration. Otherwise, the WTRU may determine that it is associated with a second TTI duration (e.g., in a window that may exclude those X ms).

[0093] 4 shows an example in which a WTRU is assigned DL resources with different TTI durations. The assignment of one or more, or multiple, TTI durations may be simultaneous. The one or more, or multiple, TTI durations may be defined per set of resource blocks (e.g., bandwidth portions) as shown in the left part of FIG. 4, or may vary over time in the set of resource blocks as shown in the right part of FIG. 4.

[0094] The embodiments contemplate TTI duration symbol mapping.

[0095] The TTI duration may not be fixed with respect to adjacent TTIs. For example, the first TTI may consist of X OFDM symbols, and / or the second TTI may consist of Y symbols, where X and Y may not be equal. The shortened TTI duration may be designed without TTI boundary synchronization with the legacy TTI duration. For example, the first TTI may include X symbols (e.g., X=7 symbols), and / or the second adjacent TTI may consist of Y symbols (e.g., Y=8 symbols). The combined first and second TTIs may not share a boundary with the legacy TTI duration (e.g., when the legacy TTI duration is 14 symbols).

[0096] The set of shortened TTIs can be designed to ensure that the set has boundaries that match those of the legacy TTIs. For example, the first TTI can include seven symbols, and / or the second TTI can include seven symbols. The first symbol of the first shortened TTI can be aligned with the first symbol of the legacy TTI, and / or the last symbol of the second shortened TTI can be aligned with the last symbol of the legacy TTI.

[0097] The shortened TTI may be applicable to a subset (e.g., only a subset) of channels, such as the PDSCH. In such a scenario, among others, the control region (e.g., the PDCCH, PCFICH, and / or PHICH) may use legacy TTI timing. The PDSCH region of the first shortened TTI may include the last XC symbols of the TTI (e.g., X may be the duration in symbols of the first shortened TTI, and C may be the duration in symbols of the control region). The PDSCH region of the second TTI may consist of one, more, or all Y symbols (e.g., Y may be the duration of the second shortened TTI).

[0098] Embodiments contemplate legacy TTI durations being subdivided into channel-specific shortened TTIs.

[0099] The legacy TTI duration may be divided into one or more, or multiple, shortened TTIs. The first shortened TTI may include (e.g., include only) the control region (e.g., the first C symbols of the legacy TTI duration). The second TTI may include at least a portion of the remaining symbols (e.g., X symbols). The third TTI may include the remaining symbols of the legacy TTI duration. In such scenarios, among others, the shortened TTI may include (e.g., completely include) the control region. Other shortened TTIs may not have a control region. The control region TTI may be used to schedule transmissions in other adjacent TTIs.

[0100] For example, a legacy TTI duration may be divided into, for example, three shortened TTIs. A first shortened TTI of duration C (e.g., C=3) symbols may include (e.g., entirely include) a control region. A second TTI of duration X (e.g., X=5) symbols may include a PDSCH and / or associated reference signals (e.g., DM-RS and CSI-RS). A third TTI of duration Y (e.g., Y=6) symbols may include another PDSCH and / or associated reference signals (e.g., DM-RS and CSI-RS). The control region of the first TTI may allocate downlink resources in the second and / or third TTIs.

[0101] The scheduling of one or more DL transmissions and / or shortened TTIs in the control region, which may possibly be applicable to, for example, one or more PDSCH TTIs, may include dependent and / or reused parameters. For example, a control region TTI may include DL allocations for two or more upcoming TTIs. The DL allocation for a first TTI may include one or more, or all, useful parameters (e.g., MCS, RB allocation, downlink allocation index, HARQ process number, precoding information, and / or HARQ-ACK resource offset). The DL allocation for a second TTI, which may be included in the same control region, may reuse one or more of the above-mentioned parameters, perhaps without explicitly indicating them, for example. The DL allocation parameters for the second TTI may be obtained as dependent on the explicitly indicated parameters of the first TTI. The dependency between the parameters of the first and second TTIs may be configured semi-statically.

[0102] In such scenarios, among others, UL transmissions may include at least two TTIs for transmission per legacy TTI duration. For example, the first UL TTI may consist of the first seven SC-FDMA symbols, and / or the second UL TTI may consist of the last seven SC-FDMA symbols. For UL scheduling, the control region in the first shortened DL TTI in legacy subframe n may grant resources in the first and / or second shortened UL TTIs of legacy subframe n+k. k may be predefined and / or may depend on the TTI duration. For example, for legacy TTI durations, k may be 4. For shortened TTI durations, k may be 2 subframes.

[0103] Embodiments contemplate variable time slot boundaries.

[0104] A TTI may be determined to be a time slot of a subframe. For example, a first TTI of a subframe may include a legacy control, channel region, and / or a PDSCH region. A second TTI of a subframe may include (e.g., only include) a PDSCH region.

[0105] In one or more techniques, the timeslot boundaries may be fixed at half the number of OFDM symbols in a subframe. In one or more techniques, the timeslot boundaries may vary. For example, the WTRU may be configured, possibly semi-statically, with timeslot boundaries for reduced TTI transmission. For example, the timeslot boundaries may be indicated in the scheduling assignment and / or scheduling grant.

[0106] The time slot boundaries may be indicated by any of the techniques described herein for indicating TTI duration.

[0107] The timeslot boundaries may be obtained implicitly by the WTRU, perhaps depending on, for example, the transport block size and MCS.

[0108] WTRUs scheduled in both time slots (e.g., TTI) of a subframe may have time slots that overlap on symbols. For example, a subframe may include 14 OFDM symbols. The first time slot may include the first 8 symbols and / or a first subset of subcarriers of the 9th symbol. The second time slot may include a second subset of subcarriers (e.g., complementary to the first subset) of subcarriers of the 9th symbol and / or the last 5 symbols. The size of the subset of subcarriers for one or more, or each, time slot may be determined as dependent on the transport block size transmitted by the WTRU in perhaps one or more, or each, time slot.

[0109] The WTRU may be assigned a (e.g., single) transport block to be transmitted over at least two, possibly adjacent, time slots (e.g., TTIs). The WTRU may segment the transport block accordingly and / or may be expected to feed back one or more or multiple HARQ A / Ns for the transport block (e.g., one per segment). The segmentation may be performed according to fixed and / or configurable rules. For example, the segmentation may be determined as being dependent on the transport block size. For example, a transport block may include one or more or multiple code blocks (e.g., one or more, or each, possibly individually encoded using, for example, a turbo encoder). The WTRU may divide the code blocks into at least two groups (e.g., equally, in a fixed manner, semi-statically, and / or dynamically indicated by the eNB). The WTRU may determine the number of useful symbols for the first and / or second time slots (e.g., including partial symbols, e.g., symbols shared by both time slots) depending on the number of REs that may be useful for transmission of one or more or each code block and / or the number of allocated resource blocks, among other scenarios.

[0110] The embodiment contemplates unequal truncated TTI duration RE mapping.

[0111] TTIs used for the same channel (e.g., TTIs used for PDSCH transmissions) may vary in duration, possibly in a fixed pattern and / or possibly indicated on a control channel. This may lead to different allowable transport block sizes per PDSCH, perhaps based on the TTI in which the PDSCH transmission occurs. The transport block size used for PDSCH transmission may be determined, for example, based on the MCS carried in the DL assignment and / or the TTI duration of the TTI in which the PDSCH transmission occurs and / or the TTI duration of the TTI in which the DL assignment is transmitted. A first MCS / TBS table may be designed for a first TTI duration and / or a second MCS / TBS table may be designed for a second TTI duration. The use of the appropriate table may be determined by the WTRU, perhaps implicitly from knowledge of the TTI duration of the PDSCH transmission.

[0112] A first MCS / TBS table may be configured for a first TTI duration, and / or a scaling formula may be used to allow the WTRU to determine the appropriate TBS for any other TTI duration.

[0113] An example of a scaling formula may be TBS_tti2=f(TBS_tti1), where TBS_tti2 may be the transport block size of the second TTI duration. TBS_tti1 may be the transport block size of the default TTI duration obtained from the MCS / TBS table. F(x) may be a pre-configured scaling function such as f(x)=floor(tti2 / tti1), where tti2 is the second TTI duration and / or tti1 may be the first TTI duration. This may enable the WTRU to operate with a wider variety of TTI durations.

[0114] The feedback provided by the WTRU may also be TTI duration dependent. The feedback may include the TTI duration for which the feedback report is valid. One or more TTI durations of the reference subframe, the measurement trigger subframe, and / or the feedback report subframe may indicate the TTI duration assumed for the feedback report measurement.

[0115] HARQ operation may be disclosed: The WTRU MAC may be configured with a separate set of HARQ processes for configured cells that support transmissions with different TTI durations.

[0116] The WTRU may be configured to use at most one TTI duration in any given subframe / slot. If the WTRU operates such that one or more, or a set of, HARQ processes associated with a particular TTI duration may be active at any given time (e.g., for cells to which the WTRU's configuration is applicable), the WTRU may replace one or more, or a set of, HARQ processes with another one or more, or a set (e.g., flush), perhaps among other scenarios, when it reconfigures the TTI lengths for those cells. If the TTI lengths are associated with different timing (e.g., the same subframe number within a frame that reoccurs in a particular period may have the same TTI length and / or different subframes within a frame may have different TTI lengths), the WTRU may maintain both sets simultaneously. The WTRU may keep some processes unused (or simply not instantiate them, e.g., to prevent two overlapping HARQ processes from being active at the same time).

[0117] The WTRU may operate with parallel TTI durations. If the WTRU operates such that HARQ processes associated with different TTI durations can be active in parallel (e.g., for cells where the WTRU's configuration is applicable), the WTRU may maintain separate HARQ processes (e.g., which set of HARQ processes is activated may depend on the TTI duration determined by the WTRU for the transmission of interest).

[0118] The WTRU may extend single connectivity. For example, the WTRU may be configured with a single MAC entity but with different sets of HARQ processes. One or more, or each set of HARQ processes, may be associated with its own C-RNTI, where control signaling received according to a first C-RNTI indicates a first TTI duration and control signaling received according to a second C-RNTI indicates a second TTI duration. The WTRU may be configured such that, for example, if the second TTI duration is configured for uplink transmission, WTRU autonomous uplink retransmissions are not performed for at least one set of HARQ processes.

[0119] The WTRU can overload dual connectivity. For example, the WTRU may be configured with one or more or multiple MAC entities (e.g., with one or more or each set of HARQ processes and / or associated with one or more or each C-RNTI). The WTRU may be configured such that the same carrier (e.g., the same cell) can be used by one or more or multiple MAC entities, whereby the one or more or each MAC entity can operate independently of each other and / or have different TTI durations. The WTRU may be configured such that WTRU autonomous uplink retransmissions are not performed for at least one MAC entity, for example, when a second TTI duration is configured for uplink transmission.

[0120] Using a timeslot duration, the WTRU can maintain eight HARQ processes for a 4 ms HARQ RTT. The WTRU can be configured to receive a PDSCH (or transmit a PUSCH) in two consecutive TTIs of shorter duration (e.g., one slot), and control parameters related to the PDSCH (or PUSCH) can be received in a single PDCCH or E-PDCCH. PDSCH (or PUSCH) transmissions can be implicitly associated with the same HARQ process, and the redundancy version of one transmission can depend on the redundancy version of the other transmission. The PDCCH or E-PDCCH can be received in the shorter TTI (e.g., one slot) duration. The WTRU can determine that this type of operation occurs in a subframe based on higher layer signaling and / or dynamic signaling, e.g., based on properties or fields of the decoded PDCCH or E-PDCCH.

[0121] The WTRU and communication system may enable a reduced TTI EPDCCH. The WTRU may be configured with an EPDCCH search space for a reduced TTI duration EPDCCH. The WTRU may be configured with an EPDCCH search space of varying TTI durations. In configuring the EPDCCH search space, the network may include one or more TTI durations for each search space. The WTRU may attempt to decode the EPDCCH for varying TTI durations using blind detection. For example, the WTRU may be configured with EPDCCH resources defined by a set of enhanced control channel elements (ECCEs), each consisting of one or more, or nine, enhanced resource element groups (EREGs). For example, the EREGs may be mapped to different REs, possibly depending on the appropriate TTI duration. The WTRU may attempt blind detection on possible RE mappings (e.g., all possible RE mappings). This may determine whether a valid EPDCCH is present.

[0122] A WTRU may be configured with a search space (or set of search spaces) for one or more, or multiple TTI durations. Upon being configured with a particular TTI duration, perhaps among other scenarios, the WTRU may determine an appropriate EPDCCH search space (or set of search spaces) in which to attempt detection. The WTRU may be configured with a search space (or set of search spaces) for multiple TTI durations and / or may perform blind detection in the search space (e.g., all search spaces or a set of search spaces). A subset of the TTI durations and / or symbols of the relevant search space may (e.g., implicitly) configure the WTRU to use that (or another) TTI duration and / or symbol subset for other channels (e.g., for granted or assigned resources).

[0123] The TTI duration of the E-PDCCH may be related to the aggregation level (e.g., number of ECCEs) of the search space. For example, the WTRU may be configured to attempt to decode E-PDCCH candidates with a TTI duration of a (e.g., single) timeslot for aggregation levels 1 and 2, and E-PDCCH candidates with a TTI duration of a subframe for aggregation levels 4 and 8.

[0124] The configured EPDCCH search space may include one or more starting OFDM symbols (or sets of OFDM symbols) for the or each search space. A WTRU may have one or more or multiple search spaces within a subframe, and one or more or each may have different locations in time within the subframe. For example, a WTRU may be configured with a first set of search spaces located (e.g., entirely) within a first timeslot and / or a second set of search spaces located (e.g., entirely) within a second timeslot. The locations of the search spaces may be configured (e.g., implicitly) with the locations of the associated channels (e.g., an EPDCCH detected in a search space within a first timeslot may lead to granted and / or assigned resources located within the first timeslot).

[0125] An EPDCCH search space may consist of one or more ECCEs. One or more, or each ECCE may be configured with a TTI duration and / or a possible symbol set. For example, a first EPDCCH search space may include ECCE0 and ECCE1. These two ECCEs may be configured for a timeslot TTI duration and / or for the first timeslot. Another EPDCCH search space may include ECCE2. This ECCE may be configured for a timeslot TTI duration, perhaps more specifically for the second timeslot. Another EPDCCH search space may consist of ECCE4, ECCE5, ECCE6, and ECCE7. These four ECCEs may be configured for a complete subframe TTI duration. One or more, or each ECCE may be repeated in one or more, or each TTI. A first EPDCCH located within a first TTI subset of symbols (e.g., the first timeslot) may consist of ECCE0 and ECCE1. A second EPDCCH located in a second TTI subset of symbols (e.g., a second time slot) may include ECCE0 and ECCE1. The RE mapping of the EREGs for one or more, or each, ECCE may depend on the location of the particular EPDCCH.

[0126] The EREG may be mapped to different REs depending on the TTI duration, for example, to enable a variable TTI duration EPDCCH. For example, for an EPDCCH using a subframe-level TTI duration, the EREG may be mapped to every 16th RE (e.g., ordered first in frequency and then in time, while skipping demodulation reference signal (DM-RS) reference elements (REs)). For a timeslot-level TTI duration, the EREG mapping may depend on the set of OFDM symbols used for a particular TTI duration. For example, the TTI duration of a timeslot may have two possible mappings for the EREG: one or more, or each, located in the first timeslot, or one or more, or each, located in the second timeslot. The EREG may use a mapping rule similar to that for the subframe-level TTI duration (e.g., the EREG is located every 16th RE, and the REs are ordered first in frequency and then in time). The first time symbol for one or more, or each, EREG mapping may be different. The EREG may be mapped to fewer than nine REs. For example, there are 72 REs (not including DM-RS REs) for one or more or each time slot: if an EREG is located every 16th RE, then 8 EREGs can have 5 REs, and 8 EREGs can have 4 REs. For reduced TTI, EREG mapping may depend on the TTI duration. For example, for a time slot-based TTI duration, an EREG can be mapped to every 8th RE, with REs ordered first in frequency and then in time. This may allow one or more or each EREG to be mapped to 9 REs (e.g., all within a single time slot - the time slot affects the first symbol an EREG can be mapped to an RE). For non-subframe or time slot TTI durations, the WTRU may be configured with an acceptable EREG to RE mapping.

[0127] For a distributed enhanced physical downlink control channel (EPDCCH), enhanced control channel elements (ECCEs) may be mapped to enhanced resource element groups (EREGs) in one or more or multiple resource blocks (RBs). One or more, or each, of the EREGs of an ECCE in the EPDCCH search space may be located within the same set of OFDM symbols. Different EREGs may be located within different sets of OFDM symbols.

[0128] Scheduling using a reduced TTI EPDCCH may be disclosed. Scheduling of PDSCH assignments or PUSCH grants with an EPDCCH may involve using one or more, or the same, TTI duration reuse for each channel, as described by way of example with reference to FIG. 5. An EPDCCH located within a subset of symbols may be assigned (or granted) PDSCH (or PUSCH) resources in the same subset of symbols, e.g., with a fixed time offset. A reduced TTI duration for the EPDCCH may lead to a reduced TTI duration for the PDSCH or PUSCH. The size and / or location of the TTI used for the EPDCCH may be reused for the PDSCH and / or PUSCH. The TTI duration and / or location of the PDSCH or PUSCH may not be tied to the TTI duration and / or location of the EPDCCH. For example, the EPDCCH can be located within a subset of symbols (e.g., the first time slot), and the assigned (and / or granted) PDSCH (and / or PUSCH) resources can be for the entire subframe (e.g., the entire subframe TTI). The EPDCCH and / or PDSCH and / or PUSCH can use a reduced TTI duration. The EPDCCH can be located within (e.g., only) the first subset of symbols. The EPDCCH within the first subset of symbols can be assigned (and / or granted) PDSCH (and / or PUSCH) resources within the second subset of symbols. For example, the EPDCCH within the first time slot can be assigned (and / or granted) PDSCH (and / or PUSCH) resources within the first time slot and / or the second time slot, e.g., in a cross-TTI scheduling manner.

[0129] Embodiments contemplate an EPDCCH spanning one or more, or multiple TTIs.

[0130] The WTRU may be configured with EPDCCH resources that may span one or more or multiple TTIs. For example, the EPDCCH resources may be configured for a legacy subframe TTI duration. The PDSCH may be configured to use a timeslot TTI duration. For DL ​​scheduling, EPDCCH resources that span one or more or multiple shortened TTIs may be used, perhaps to allocate resources to any of the TTIs that the EPDCCH may span. A downlink allocation indicated in an EPDCCH that spans one or more or multiple shortened TTIs may include an index to indicate which of the shortened TTIs the allocation is for (e.g., located in the same legacy subframe as the EPDCCH).

[0131] Embodiments contemplate the use of EPDCCH DM-RS. Demodulation using DM-RS may be used, for example, to enable EPDCCH. For a shortened TTI duration EPDCCH, DM-RS may be available in some of the EPDCCH symbols. For example, for a timeslot TTI duration, one or more, or each timeslot, may have enough DM-RS to enable four ports. The EPDCCH search space (e.g., the entire EPDCCH search space) may use spatial multiplexing, and the same EREG may be used for up to four EPDCCH search spaces. For smaller TTI durations, DM-RS may be redesigned to enable DM-RS in OFDM symbols. The set of symbols for a TTI duration may include at least one symbol with DM-RS (e.g., symbols 5, 6, 12, and 13 of a subframe for a normal cyclic prefix). For example, with four DM-RS symbols, the TTI may be approximately ¼ of a subframe. By ignoring legacy subframe boundaries, the shortened TTI subset of the first symbol can be symbols 2, 3, 4, and 5 (with DM-RS in symbol 5), the shortened TTI subset of the second symbol can be symbols 6, 7, and 8 (with DM-RS in symbol 6), the shortened TTI subset of the third symbol can be symbols 9, 10, 11, and 12 (with DM-RS in symbol 12), and the shortened TTI subset of the fourth symbol can be symbols 13, 0 (in the next subframe), and 1 (in the next subframe) (with DM-RS in symbol 13). Given that DM-RS doubles the number of possible ports using frequency orthogonality in such scenarios, among others, one or more, or each, TTI subset of symbols can have up to two DM-RS ports, and one or more, or each, TTI subset of symbols can spatially multiplex two EPDCCH search spaces onto the same set of EREGs.

[0132] The system may use asymmetric TTI durations. The TTI duration for the UL-SCH may be different from that used for DL-SCH transmissions. For example, the DL-SCH may use a timeslot TTI duration and the UL-SCH may use a subframe TTI duration. For example, to allow for such asymmetric TTI durations, one or more of the following may be implemented:

[0133] The system may use a shortened TTI for the DL-SCH or a subframe TTI for the UL-SCH. Reduced TTI DL-SCH scheduling may be achieved by using an EPDCCH in the manner described herein. The PDCCH may be used to allocate PDSCH resources to the WTRU. The (E)PDCCH located at the beginning of a subframe may be used to schedule data in a shortened TTI subset (e.g., TTI duration) of any symbol within the subframe, as shown, for example, in FIG. 5. The (E)PDCCH located at the beginning of a subframe may explicitly indicate to the WTRU the TTI subset of symbols to which the scheduling assignment pertains. Parameters of the (E)PDCCH located at the beginning of a subframe may indicate the TTI subset of symbols to which the scheduling assignment pertains. One or more of the following may be configured to indicate the shortened TTI subset of relevant symbols of the scheduling allocation: the first (or second) CCE of the DCI, the DCI format, the PUCCH resources configured for HARQ ACK-NACK, the modulation and coding scheme (MCS) (e.g., some MCSs may be reserved for specific shortened TTI subsets of symbols), and / or the pre-configured PDSCH RE mapping and quasi-co-location indicator (PQI).

[0134] At the beginning of one or more, or each, shortened TTI subset of symbols, a PDCCH-like channel may be transmitted. In such scenarios, among others, PDSCH transmissions for the shortened TTI subset of symbols may be allocated (e.g., only allocated) by a PDCCH located within one (or many) symbols at the beginning of the shortened TTI subset of symbols. For example, in a single-timeslot TTI duration, a PDCCH may be located within one or more, or the first symbol of each, time slot to enable single-timeslot-per-TTI PDSCH allocation.

[0135] The system can use UCI feedback for the shortened TTI DL-SCH. The ECCEs for a subframe (e.g., all ECCEs) are defined for a specific subset of symbols within the subframe (e.g., the first x ECCEs are assigned to a first time slot, the next y ECCEs are assigned to a second time slot), and the resources used for HARQ ACK-NACK feedback in subframe n+i can depend on the first (or second) ECCE of the DCI for the PDSCH allocation. In scenarios where the same ECCE labeling can be used one or more or multiple times within a subframe (e.g., one or more, or each, for every shortened TTI duration), the HARQ ACK-NACK feedback resources can overlap, e.g., if they depend solely on the first (or second) ECCE of the DCI for the PDSCH allocation. In this situation, the resource used for HARQ ACK-NACK feedback in subframe n+i may depend on both the first (or second) ECCE of the DCI for the PDSCH allocation and the symbol configuration used for the EPDCCH. For example, the ACK-NACK feedback resource may depend on the first (or second) ECCE of the DCI for the PDSCH and the first (or second) OFDM symbol used for the ECCE.

[0136] The WTRU may determine resources for PUCCH transmission as dependent on a configuration of distinct sets of PUCCH resources, including distinct PUCCH regions, where one or more, or each, resource set may correspond to transmission according to a different TTI duration. For a second TTI duration, the WTRU may transmit (e.g., transmit only) HARQ ACK-NACK feedback on such PUCCH resource allocation. The WTRU may receive downlink data according to the first TTI length and / or transmit uplink control information according to the second TTI length (e.g., in a scenario where the WTRU may have a configuration allowing one or more, or multiple, TTI durations in parallel). In such scenarios, among others, the WTRU may select resources and / or transmission formats for UCI (e.g., UCI on PUSCH, PUCCH format 1a / 1b, and / or PUCCH format 3, etc.) depending on whether the included UCI is associated with a transmission received according to a single TTI length (e.g., using legacy PUCCH format and resource selection) or whether the included UCI is associated with a transmission received according to one or more, or multiple TTI lengths (e.g., using alternative PUCCH formats and / or resources).

[0137] Among other scenarios, perhaps when a WTRU is scheduled with one or more PDSCHs, e.g., one per shortened TTI subset of symbols, the WTRU may bundle and / or multiplex its HARQ ACK-NACK feedback onto one (or more) feedback resources. The feedback resources may be determined from the first (or second) ECCE in the shortened TTI subset of the first (or second) symbol. For example, a WTRU scheduled with a PDSCH with two EPDCCHs, one in the first timeslot and the second in the second timeslot, may bundle and / or multiplex its HARQ ACK-NACK feedback onto resources determined by the first (and / or second) ECCE of the EPDCCH located in the first (and / or second) timeslot.

[0138] In scenarios where one or more or multiple TTI HARQ ACK-NACK feedbacks may be included in the same feedback resource (e.g., by multiplexing and / or bundling), among other scenarios, there may be differences in processing time for generating appropriate feedback for one or more or each TTI. The HARQ ACK-NACK resource may be located within legacy subframe n+k, where n may be the legacy subframe in which the first TTI DL transmission is included, and / or k may be any integer equal to or greater than 1. For example, if a legacy subframe is divided into two equal-length DL transmission TTIs (e.g., one per timeslot) and k=1, the WTRU may begin transmitting HARQ ACK-NACK feedback upon receiving (e.g., immediately after) the last symbol of the second timeslot TTI. Among other reasons, perhaps to allow sufficient processing time, particularly for correct decoding of the second TTI, the TTIs may be offset to multiplex and / or bundle with one or more HARQ ACK-NACK feedbacks. For example, feedback for the second timeslot TTI from subframe n may be combined (e.g., multiplexed and / or bundled) with feedback for the first timeslot TTI from subframe n+1 into a HARQ ACK-NACK feedback report in subframe n+1+k, where k is an integer greater than or equal to 1. Some DL allocation constraints may be imposed on the second TTI transmission, perhaps to address uneven processing times, among other reasons, for example because the WTRU may have less time to determine the feedback than the first TTI transmission. The constraint(s) may be indicated by the WTRU in the form of WTRU capabilities. The constraint(s) may play a role, among other scenarios, when DL allocation parameters for the second TTI may be determined as dependent on the DL allocation parameters of the first TTI transmission.

[0139] Different shortened TTIs may have different HARQ timelines. For example, a first set of shortened TTIs may have HARQ ACK-NACK feedback in a legacy subframe and / or shortened TTI n+k_1 (e.g., n may be a legacy subframe and / or shortened TTI in which a DL transmission occurs, and / or k_1 may be a counter of legacy subframes and / or shortened TTIs). A second set of shortened TTIs may have HARQ ACK-NACK feedback in a legacy subframe and / or shortened TTI n+k_2. The set of TTIs with one or more, or respectively different HARQ timelines, and / or the values ​​of k_1 and k_2 may be semi-statically configured and / or cell-specific and / or WTRU-specific. The set of TTIs and / or the values ​​of k_1 and / or k_2 may depend on the TTI duration. For example, one or more or all 1 ms duration TTIs may use k_1=4 legacy subframes, and one or more or all 0.5 ms duration TTIs may use k_2=4 shortened TTI=2 legacy subframes.

[0140] The WTRU may be configured with a table of HARQ ACK-NACK resources. Within the DCI of the PDSCH allocation, the network may indicate one or more appropriate ACK-NACK resources for each feedback.

[0141] The timing of the HARQ ACK-NACK feedback may be defined as n+i, where "n" is the subframe number in which the PDSCH is transmitted and "i" may be a predetermined offset measured in subframes. For example, "n" may represent a counter of the shortened TTI subset of symbols and / or "i" may be a predetermined offset measured in the shortened TTI subset of symbols. For example, for a timeslot TTI duration, one or more, or each timeslot in a frame, may be numbered and used for "n," and the value of "i" may be 4 timeslots. A combination of interpretations of "n" (e.g., subframe number, timeslot number, OFDM symbol number of the first symbol of the PDSCH) and / or "i" (e.g., subframe number, timeslot number, OFDM symbol number) may be used. The WTRU may be statically and / or semi-statically configured with the feedback timing interpretation. The WTRU may be configured with the feedback timing interpretation, perhaps, for example, as soon as resources for a shortened TTI PDSCH transmission are allocated.

[0142] For UCI on the PUSCH, the HARQ ACK-NACK may be mapped to REs adjacent to the UL DM-RS. In scenarios where a single subframe may comprise one or more or multiple shortened TTI subsets of symbols, among other scenarios, one or more or each HARQ ACK-NACK may be transmitted on the PUSCH. The set of HARQ ACK-NACKs may be mapped to REs adjacent to the UL DM-RS, e.g., in a preconfigured manner. For example, the first ACK-NACK may be mapped to REs adjacent to the UL DM-RS (e.g., symbols 2 and 4 and symbols 9 and 11 if the UL DM-RS is located in symbols 3 and 10). The second ACK-NACK may be mapped to REs in the next symbol (e.g., symbols 1 and 5 and symbols 8 and 12), and so on. The first ACK-NACK may be mapped around the first UL DM-RS (e.g., symbols 2 and 4). The second ACK-NACK may be mapped to REs around the second UL DM-RS (eg, symbols 9 and 11).

[0143] Embodiments contemplate HARQ-ACK reporting using one or more, or multiple TTI durations.

[0144] One or more techniques contemplate how a WTRU may report a HARQ-ACK in a subframe, for example, in a scenario in which the TTI duration of a previous transmission may be determined in a dynamic manner, among other scenarios.

[0145] In some techniques, perhaps among other scenarios, for a given subframe in which a HARQ-ACK may be transmitted, the WTRU may determine that HARQ-ACK information is reported for one or more, or every possible transport block associated with any TTI duration that may have been transmitted in the previous subframe according to its HARQ timing and / or semi-static configuration (e.g., perhaps regardless of whether a transmission actually occurred). For example, in subframe n the WTRU may report HARQ-ACK for one or more of the following: - a transport block associated with the first TTI duration (e.g., 1 ms) that may have been received in subframe n-k1 (e.g., k1=4), and / or - A transport block associated with a second TTI duration (e.g., 0.5 ms) that may have been received in subframe n-k2 (e.g., k2=2) and / or in a specific part of subframe n-k2 (e.g., the first timeslot).

[0146] In scenarios where the WTRU may not detect a transmission for a given transport block, the WTRU may report a NACK and / or DTX for this transport block.

[0147] The WTRU may provide an indication of the TTI duration associated with a transport block or set of transport blocks for which HARQ-ACK information was reported in a subframe. In some techniques, the indication may be for the subframe in which the transport block was received. For example, the indication may have a first value when the HARQ-ACK information is provided for a transport block associated with a first TTI duration, a second value when the HARQ-ACK information is provided for a transport block associated with a second TTI duration, and / or a third value when the HARQ-ACK information is provided for a transport block of any TTI duration.

[0148] The WTRU may determine that for a selected subset of transport blocks, HARQ-ACK information is to be reported. The selection may be based on one or more priority criteria, which may include one or more of the following: - The TTI duration associated with the transport block, e.g., a higher priority may be given to smaller TTI durations; - the time elapsed since the initial HARQ transmission of the transport block, e.g. the priority may be higher for transport blocks whose initial HARQ transmission started earlier; - redundancy version, retransmission sequence number, and / or number of HARQ transmissions for the transport block; - the type of transport channel through which the transport block was transferred, e.g., the priority may be higher for transport channels that may be defined with the purpose of allowing low latency and / or highly reliable communication; - the type of physical control channel and / or physical data channel that may be used for the transmission of the transport block; - at least one transmission parameter associated with the transport block, such as a parameter corresponding to a device-to-device transmission and / or a transmission to or from a network; and / or - The MAC instance or cell group associated with the transport block.

[0149] Systems and methods for reduced-TTI duration PUCCH may be provided. Given that a reduced-TTI PDSCH may lead to an increased number of independent PDSCH allocations in any subframe, an increase in PUCCH resources may accommodate feedback. The OFDM symbols used for the ECCE of the EPDCCH and / or the PDSCH itself may indicate to the WTRU the symbols on which the PUCCH may be transmitted in the UL. For example, if a timeslot-based EPDCCH / PDSCH is used, an allocation in the first (or second) timeslot may use PUCCH feedback using the first (or second) timeslot of the appropriate feedback subframe (e.g., only the first (or second) timeslot). This may allow for two PDSCH allocations in one or more, or each, of the timeslots of a single subframe, and one or more, or each, mapping (e.g., by PUCCH RB position and / or cyclic shift and / or orthogonal cover code) to the same PUCCH resource may be orthogonalized by one or more, or each, using a single timeslot.

[0150] The PUCCH may be located at the edge of the overall available spectrum. This may maximize frequency diversity. The same SC-FDMA symbol may be reused to transmit the PUCCH at both edges of the overall bandwidth. For example, as shown in FIG. 6, for a single-timeslot TTI duration, PUCCH format 1 may repeat the same data in one or more, or two RBs located at each edge of the available bandwidth, and in the same time slot. Cyclic shifts and OCC sequence randomization may be defined per PUCCH RB, rather than per time slot. PUCCH resources may be transmitted at the edges of the bandwidth and may occupy half (e.g., only half) of the reduced TTI subset of symbols in a similar manner as for a subframe TTI duration (e.g., as in FIG. 7). Legacy PUCCH formats 2 and 3 cannot repeat the same transmission at the edges of the available bandwidth. Nevertheless, similar to single timeslot TTI PUCCH format 1, single timeslot TTI PUCCH formats 2 and / or 3 may use one or more, or each, two RBs located at the edge of the available bandwidth and / or within the same timeslot. For PUCCH formats 2 and / or 3, one or more, or each, RB at the edge of the same timeslot may not be a repetition of the same data, but instead may contain different UCI bits.

[0151] The feedback report on the PUCCH may be repeated across one or more, or multiple PUCCH resources, perhaps within one legacy subframe in some techniques. This may allow the eNB to achieve faster retransmission of data (e.g., when useful). For example, perhaps among other scenarios, if a NACK is detected in the first transmission of the PUCCH, the eNB may prepare for retransmission in the next DL subframe.

[0152] The disclosed methods and systems apply to PDSCH DM-RS. Similar DM-RS features may be useful for PDSCH as shown herein for EPDCCH. PDSCH can use up to eight transmit ports. A reduced TTI duration PDSCH may allow DM-RS for up to eight transmit ports. In a single timeslot TTI duration, OCC and frequency multiplexing may allow DM-RS to support up to four ports. To increase DM-RS capacity, DM-RS may not repeat every fifth subcarrier within an RB. For example, DM-RS for ports 0 and 1 may be transmitted on subcarriers 1 and 11, and DM-RS for ports 4 and 6 may be transmitted on subcarrier 6. DM-RS for ports 2 and 3 may be transmitted on subcarriers 0 and 10, and DM-RS for ports 5 and 7 may be transmitted on subcarrier 5. RB bundling in the frequency domain may be used to keep the total number of subcarriers for one or more, or each, DM-RS port constant for a pair of RBs. For example, DM-RS for ports 0 and 1 may be transmitted in subcarriers 1 and 11 of the first RB and subcarrier 6 of the second RB. DM-RS for ports 4 and 6 may be transmitted in subcarrier 6 of the first RB and subcarriers 1 and 11 of the second RB. DM-RS for ports 2 and 3 may be transmitted in subcarriers 0 and 10 of the first RB and subcarrier 5 of the second RB. DM-RS for ports 5 and 7 may be transmitted in subcarrier 5 of the first RB and subcarriers 0 and 10 of the second RB. DM-RSs may occupy more subcarriers than a complete subframe TTI. For example, the DM-RS for ports 0 and 1 may be located in subcarriers 1 and 7, the DM-RS for ports 2 and 3 may be located in subcarriers 0 and 6, the DM-RS for ports 4 and 6 may be located in subcarriers 4 and 10, and the DM-RS for ports 5 and 7 may be located in subcarriers 3 and 9.

[0153] The disclosed methods and systems may enable a shortened TTI for the UL-SCH. The disclosed methods and systems may relate to scheduling a shortened TTI UL-SCH. Reduced TTI UL-SCH scheduling may be achieved by using an EPDCCH as described herein. A PDCCH may be used to grant PUSCH resources to a WTRU. An (E)PDCCH located at the beginning of a subframe may be used to grant PUSCH resources in a shortened TTI subset of symbols in subframe n+i. The timing of the scheduled grant may be defined as n+i, where "n" may be the subframe number in which the (E)PDCCH is transmitted and "i" is a predetermined offset measured in subframe numbers. "n" may represent a counter of the shortened TTI subset of symbols for any preconfigured channel TTI duration. For example, the shortened TTI duration of the (E)PDCCH channel may be used as the counter. and "i" may be a predetermined offset measured on a shortened TTI subset of symbols (e.g., also of the TTI duration of the preconfigured channel). For example, for a timeslot TTI duration, one or more, or each timeslot in a frame may be numbered, and / or the timeslot used for the (E)PDCCH may be used for n, and the value of i may be 4 timeslots. A combination of interpretations of n (e.g., subframe number, timeslot number, OFDM symbol number of the first symbol of the preconfigured channel) and i (e.g., subframe number, timeslot number, OFDM symbol number) may be used. The WTRU may be statically and / or semi-statically configured with the resource grant timing interpretation. Among other scenarios, the WTRU may be configured with the resource grant timing interpretation, perhaps as soon as resources for a shortened TTI PUSCH transmission are granted, for example.

[0154] The (E)PDCCH located at the beginning of a subframe may indicate (e.g., explicitly) to the WTRU the TTI subset of symbols to which the scheduling grant is relevant. Parameters of the (E)PDCCH located at the beginning of a subframe may indicate the TTI subset of symbols to which the scheduling grant is relevant. One or more of the following may be configured to indicate the shortened TTI subset of symbols to which the scheduling grant is relevant: the first (or second) CCE of the DCI, the DCI format, the PHICH resources configured for HARQ ACK-NACK, and / or the MCS. Some MCSs may be reserved for the shortened TTI subset of specific symbols.

[0155] Parameters for UL transmission in a first shortened TTI may be reused for UL transmission in a second shortened TTI. UL granted parameters, such as UL power control, may remain constant for the entire legacy subframe and / or may be reused for one or more, or multiple, shortened TTIs. For example, UL power control parameters for a second shortened TTI transmission in a legacy subframe may be based on, among other scenarios, dependent UL power control parameters for a first shortened TTI transmission, perhaps in the same legacy subframe. Such parameter relationships between two shortened TTI transmissions may depend on the contents of the shortened TTIs. For example, perhaps two adjacent shortened TTIs are granted for PUSCH data transmission, and they may reuse some parameters (e.g., UL power control, MCS, precoding, RB allocation, cyclic shift for DM-RS, and / or OCC index, and / or downlink allocation index). For example, perhaps if two adjacent shortened TTIs are allowed, one for data (e.g., exclusively) and / or the second for data and / or UCI, the relationship between the parameters may be different, e.g., the UL power control of the data TTI (e.g., data-only TTI) may not be reused identically for the data and / or UCI TTIs.

[0156] One or more techniques may enable PHICH resource allocation. One or more, or each, transport block and TTI may have independent PHICH resources. Perhaps, for example, among other scenarios, to enable a shortened TTI duration for the UL-SCH, a WTRU may be scheduled with one or more, or multiple PUSCHs whose TTI duration is smaller than a subframe (e.g., within a subframe). Such a WTRU may be assigned one or more, or multiple PHICH resources (e.g., one per transport block and per shortened TTI subset of symbols) to be fed back in subframe n+i. The PHICH resources (e.g., number of PHICH groups, number of orthogonal sequences, RE resources in frequency and OFDM symbol) may be determined from one or more of the following: the first or second resource block in which the corresponding PUSCH transmission occurred, the first or second OFDM symbol in which the corresponding PUSCH transmission occurred, the time slot in which the corresponding PUSCH transmission occurred, the UL DM-RS cyclic shift, and / or whether the shortened TTI transmission occurred in the first or second slot of the subframe.

[0157] The PHICH may be transmitted in the same TTI subset of symbols as the (E)PDCCH used to grant the PUSCH resource. For example, assuming a timeslot TTI duration, if the (E)PDCCH used to grant the PUSCH transmission is located in the first timeslot of subframe n, the PHICH associated with that PUSCH transmission may be located in the first timeslot of subframe n+8.

[0158] The PHICH may be transmitted in a shortened TTI subset of symbols within subframe n+4, and the location (in terms of OFDM symbols) may be pre-configured or determined as part of a function for determining the PHICH resources for one or more, or each, PUSCH.

[0159] The PHICHs for one or more, or multiple TTIs within a subframe may collide. In such scenarios, among others, the WTRU may bundle and / or multiplex the PHICH values ​​onto the same PHICH resource.

[0160] The timing of the PHICH can be defined as n+i, where n can be the subframe number in which the (E)PDCCH is transmitted or the subframe number in which the PUSCH is transmitted, and "i" is a predetermined offset measured in subframes. "n" can represent a counter of a shortened TTI subset of symbols of the TTI duration of the preconfigured channel. For example, the shortened TTI duration of the (E)PDCCH transmission (or PUSCH transmission) can be used as the counter. And "i" can be a predetermined offset measured in the shortened TTI subset of symbols (also of the TTI duration of the preconfigured channel). For example, for a timeslot TTI duration, one or more, or each, timeslot in a frame can be numbered, and the timeslot used for the (E)PDCCH (or PUSCH) can be used for "n", and the value of "i" can be 8 (or 4) timeslots. A combination of interpretations of "n" (e.g., subframe number, time slot number, OFDM symbol number of the first symbol of the preconfigured channel) and "i" (e.g., number of subframes, time slots, number of OFDM symbols) may be used. The WTRU may be statically or semi-statically configured with the PHICH timing interpretation. The WTRU may be configured with the PHICH timing interpretation as soon as resources for a shortened TTI PUSCH transmission are granted.

[0161] The WTRU may expect (e.g., only expect) PHICH transmissions for a subset of shortened TTI PUSCH transmissions in a subframe (e.g., all shortened TTI PUSCH transmissions). For other PUSCH transmissions, the WTRU may assume an ACK unless a new grant is given for adaptive retransmission. For example, for a timeslot TTI duration, a PUSCH transmission in a first timeslot (e.g., only a PUSCH transmission in the first timeslot) may have PHICH resources, and a PUSCH transmission in a second timeslot may assume an ACK unless resources are granted for retransmission.

[0162] The method and system provide frequency diversity for shortened-TTI PUSCH transmissions. Frequency hopping may be used to achieve frequency diversity for PUSCH transmissions. Frequency hopping may be used by dividing a shortened-TTI subset of symbols into two groups and mapping a different shortened virtual resource block to one or more, or each, groups. The shortened virtual resource blocks may be mapped to different shortened physical resource blocks using different subcarriers, increasing frequency diversity. For example, a PUSCH transmitted in the first time slot may use two shortened virtual resource blocks: the first is mapped to symbols 0, 1, and 2, and the second is mapped to symbols 4, 5, and 6. In this example, the UL DM-RS may be transmitted in symbol 3. Mapping to shortened physical resource blocks may enable frequency diversity by ensuring that a single PUSCH shortened resource block pair (e.g., in this example, the shortened resource block pair consists of seven OFDM symbols) is mapped to different shortened physical resource blocks using different subcarriers. For demodulation, the UL DM-RS in symbol 3 can be used to demodulate the shortened resource blocks located in symbols 0, 1, and 2, or the shortened resource blocks located in symbols 4, 5, and 6.

[0163] The shortened PUSCH frequency hopping can be achieved by repeating the shortened RB pair in different subcarriers, e.g., the PUSCH of a time slot TTI can be transmitted in the first time slot of a first physical resource block pair and in the first time slot of a second physical resource block pair.

[0164] The system may use a UL DM-RS shortened TTI PUSCH. To achieve full UL DM-RS capacity, two UL DM-RS symbols may be used per RB pair (where an RB pair is defined as the TTI duration). Two symbols may be allocated for UL DM-RS transmission within a shortened TTI subset of symbols. These symbols may be pre-configured and / or semi-statically configured and / or may be indicated in the grant allocating PUSCH resources. For example, in a timeslot TTI duration, a WTRU allocated a PUSCH resource in the first timeslot may transmit UL DM-RS in symbols 2 and 5 (or any other configured symbol pair).

[0165] Although features and elements have been described above in particular combinations, those skilled in the art will understand that each feature or element may be used alone or in any combination with the other features and elements. Furthermore, the methods described herein may be implemented in a computer program, software, or firmware embodied in a computer-readable medium for execution by a computer or processor. Examples of computer-readable media include electronic signals (transmitted over wired or wireless connections) and computer-readable storage media. Examples of computer-readable storage media include, but are not limited to, ROM, RAM, registers, cache memory, semiconductor memory devices, magnetic media such as internal hard disks and removable disks, magneto-optical media, and optical media such as CD-ROM disks and digital versatile disks (DVDs). A processor in association with software may be used to implement a radio frequency transceiver for use in a WTRU, UE, terminal device, base station, RNC, or any host computer.

Claims

1. A device comprising a processor, The processor: determining a duration associated with the first transmission; determining a downlink control information format indicating the duration associated with the first transmission; transmitting a downlink control channel transmission, the downlink control channel transmission including downlink control information using the downlink control information format; transmitting the first transmission, the first transmission using the duration determined in accordance with the downlink control information format used in the transmitted downlink control channel transmission; A device configured to run

2. 10. The device of claim 1, wherein the first transmission is a physical downlink shared channel (PDSCH) transmission that uses the duration.

3. The device of claim 1 , wherein the device is a base station.

4. A device comprising a processor, The processor: determining a duration associated with the first transmission; determining a downlink control information format indicating the duration associated with the first transmission; transmitting a downlink control channel transmission, the downlink control channel transmission including downlink control information using the downlink control information format indicating the duration associated with the first transmission; A device configured to run

5. The device of claim 4 , wherein the processor is further configured to send the first transmission.

6. 6. The device of claim 5, wherein the first transmission is a physical downlink shared channel (PDSCH) transmission that uses the duration.

7. The device of claim 4 , wherein the processor is further configured to receive a second transmission.

8. The device of claim 4 , wherein the device is a base station.

9. 5. The device of claim 4, wherein the processor is further configured to transmit the first transmission, the first transmission using the duration in accordance with the downlink control information format used in the transmitted downlink control channel transmission.

10. determining a duration associated with the first transmission; determining a downlink control information format indicating the duration associated with the first transmission; transmitting a downlink control channel transmission, the downlink control channel transmission including downlink control information using the downlink control information format indicating the duration associated with the first transmission; A method for providing the above.

11. The method of claim 10 , further comprising transmitting the first transmission.

12. 12. The method of claim 11, wherein the first transmission is a physical downlink shared channel (PDSCH) transmission using the duration.

13. The method of claim 10 , further comprising receiving a second transmission.

14. The method of claim 10 , wherein the method is performed by a device, the device being a base station.

15. 11. The method of claim 10, further comprising transmitting the first transmission, the first transmission using the duration in accordance with the downlink control information format used in the transmitted downlink control channel transmission.

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