Method and procedure for downlink physical channels for reducing latency in extended LTE system

Abstract

To provide a method, a system, and an apparatus for reducing latency in extended LTE transmission.SOLUTION: A method, a system, and an apparatus uses short transmission time interval (sTTI) resource types and sTTI resource configurations for reduced latency transmission. Design for an sTTI indicator for dynamic sTTI resource presence and / or sTTI resource type indication may be disclosed. Embodiments may include sPDCCH blind decoding complexity handling based on the number of sPDCCH regions within a sTTI window. Joint sPDCCH and normal PDCCH (nPDCCH) search space configurations may be disclosed. Reference signal overhead control for sPDCCH / sPDSCH based on the number of bundled sTTI and / or one or more link adaptation parameters (e.g., MCS level) may be disclosed. A sCCE based sPDCCH and sPDSCH transmission scheme may also be disclosed.SELECTED DRAWING: Figure 10

Description

[Technical Field]

[0001] The present invention relates to a method and procedure for a downlink physical channel to reduce latency in an enhanced LTE system. [Background technology]

[0002] CROSS-REFERENCE TO RELATED APPLICATIONS This application claims the benefit of U.S. Provisional Patent Application No. 62 / 315,404, filed March 30, 2016, U.S. Provisional Patent Application No. 62 / 334,886, filed May 11, 2016, and U.S. Provisional Patent Application No. 62 / 373,046, filed August 10, 2016, the contents of all of which are incorporated herein by reference.

[0003] Low-latency cellular communications, including machine-type communications (MTC), are rapidly becoming more important as new applications for cellular technology emerge, such as alarm reporting, automotive safety, and factory process control. For example, in enhanced LTE (LTE-A) systems, the typical 1 ms transmission time interval (TTI) and associated latency may no longer be sufficient. Existing applications such as gaming and real-time applications such as VoLTE and video telephony / conferencing may also benefit from reduced latency, e.g., in terms of a higher perceived quality of experience. Summary of the Invention

[0004] A method for a wireless transmit / receive unit (WTRU) for receiving control information for reduced transmission time interval (sTTI) communications is disclosed. The method may include receiving a configuration for one or more sTTI resources, receiving an indication of the presence of the configured sTTI resources, and monitoring a reduced PDCCH (sPDCCH) within the configured sTTI resources using a number of blind decode candidates. The number of blind decode candidates may be based on a length of the sTTI. The indication may be received on a physical hybrid ARQ indicator channel (PHICH). The configuration of the sTTI resources may be received within the sTTI indicator. The sTTI indicator may be based on a set of PHICH resources. [Brief explanation of the drawings]

[0005] A more detailed understanding may be had from the following description, given by way of example in conjunction with the accompanying drawings, in which:

[0006] [Figure 1A] FIG. 1 is a system diagram of an example communication system in which one or more disclosed embodiments may be implemented. [Figure 1B] 1B is a system diagram of an example wireless transmit / receive unit (WTRU) that may be used within the communication system shown in FIG. 1A. [Figure 1C] 1B is a system diagram of an example radio access network and an example core network that may be used within the communication system shown in FIG. 1A. [Figure 2] FIG. 1 illustrates a conventional hybrid automatic repeat request (HARQ) and HARQ for reduced transmission time interval (sTTI). [Figure 3] A diagram showing the use of legacy EPDCCH for sTTI resource scheduling. [Figure 4] FIG. 1 is a diagram of an example of a resource element group (REG). [Figure 5] FIG. 1 is a diagram of an example of a resource element group (REG). [Figure 6]FIG. 1 illustrates allocation of Physical Control Format Indicator Channel (PCFICH) REGs by Physical Cell ID (PCI). [Figure 7] FIG. 1 illustrates a PCI-based PCFICH and Physical Hybrid ARQ Indicator Channel (PHICH) REG. [Figure 8] A diagram showing multiple sTTI resource types configured within a subframe. [Figure 9] FIG. 1 is a diagram of a control region location for a reduced transmission time interval indicator (sTTI indicator). [Figure 10] FIG. 1 is a diagram of a control region location for a reduced transmission time interval indicator (sTTI indicator). [Figure 11] FIG. 1 illustrates sTTI physical downlink control channel (sPDCCH) and sTTI physical downlink shared channel (sPDSCH) association per sTTI. [Figure 12] FIG. 1 illustrates multiple sPDCCH and sPDSCH associations. [Figure 13] A diagram illustrating the use of PHICH resources as sTTI indicators. DETAILED DESCRIPTION OF THE INVENTION

[0007] 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 methods, 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.

[0008] 1A, communications system 100 may include wireless transmit / receive units (WTRUs) 102a, 102b, 102c, and 102d, a radio access network (RAN) 104, a core network 106, a public switched telephone network (PSTN) 108, the Internet 110, and other networks 112, although it should be understood that the disclosed embodiments contemplate any number of WTRUs, base stations, networks, and / or network elements. Each of WTRUs 102a, 102b, 102c, and 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, and 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, cellular phones, personal digital assistants (PDAs), smartphones, laptops, netbooks, personal computers, wireless sensors, consumer electronics devices, etc.

[0009] 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 and facilitate access to one or more communications networks, such as the core network 106, 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 evolved Node B, a home Node B, an evolved home Node B, 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 should be understood that the base stations 114a, 114b may include any number of interconnected base stations and / or network elements.

[0010] The base station 114a may be part of the RAN 104, which may 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, sometimes 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, i.e., one transceiver for each sector of the cell. In another embodiment, the base station 114a may use multiple-input multiple-output (MIMO) technology and thus may use multiple transceivers for each sector of the cell.

[0011] The base stations 114a, 114b may communicate with one or more of the WTRUs 102a, 102b, 102c, 102d over an air interface 116, which may be any suitable wireless communications link (e.g., radio frequency (RF), microwave, infrared (IR), ultraviolet (UV), visible light, etc.). The air interface 116 may be established using any suitable radio access technology (RAT).

[0012] More specifically, as noted above, the communications 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 RAN 104 may implement a radio technology such as Universal Mobile Telecommunications System (UMTS) Terrestrial Radio Access (UTRA), which may establish the air interface 116 using Wideband CDMA (W-CDMA). WCDMA may include communications 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).

[0013] 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 Network (E-UTRA), which may establish the air interface 116 using Long Term Evolution (LTE) and / or Enhanced LTE (LTE-A).

[0014] In other embodiments, the base station 114a and the WTRUs 102a, 102b, 102c may implement a wireless technology such as IEEE 802.16 (i.e., Worldwide Interoperability for Microwave Access (WiMAX)), CDMA2000, CDMA2000 IX, 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.

[0015] 1A may be, for example, a wireless router, a Home Node B, a Home evolved Node B, or an access point and may use any suitable RAT for facilitating wireless connectivity in a local area, such as a business, home, vehicle, 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 yet another embodiment, the base station 114b and the WTRUs 102c, 102d may use a cellular-based RAT (e.g., WCDMA, CDMA2000, GSM, LTE, LTE-A, etc.) to establish a picocell or femtocell. 1A, the base station 114b may have a direct connection to the Internet 110. Thus, the base station 114b may not be required to access the Internet 110 through the core network 106.

[0016] The RAN 104 may communicate with the core network 106, which may be any type of network configured to provide voice, data, application, and / or Voice over Internet Protocol (VoIP) services to one or more of the WTRUs 102a, 102b, 102c, 102d. For example, the core network 106 may provide call control, billing services, mobile location-based services, prepaid calling, Internet connectivity, video distribution, etc., and / or perform high-level security functions such as user authentication. Although not shown in FIG. 1A , it should be understood that the RAN 104 and / or core network 106 may communicate directly or indirectly with other RANs that use the same RAT as the RAN 104 or a different RAT. For example, in addition to being connected to the RAN 104, which may be using E-UTRA radio technology, the core network 106 may also communicate with another RAN (not shown) that uses GSM radio technology.

[0017] The core network 106 may also serve as a gateway for the WTRUs 102a, 102b, 102c, 102d to access the PSTN 108, the Internet 110, and / or other networks 112. The PSTN 108 may include a circuit-switched telephone network providing basic telephone service (POTS / plain old telephone service). The Internet 110 may include a global system of interconnected computer networks and devices that use common communication protocols, such as Transmission Control Protocol (TCP), User Datagram Protocol (UDP), and Internet Protocol (IP) in the TCP / IP Internet protocol suite. The networks 112 may include wired or wireless communication networks owned and / or operated by other service providers. For example, the network 112 may include another core network connected to one or more RANs that may use the same RAT as the RAN 104 or a different RAT.

[0018] 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 that may use a cellular-based radio technology and a base station 114b that may use an IEEE 802.11 radio technology.

[0019] 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 global positioning system (GPS) chipset 136, and other peripherals 138. It should be understood that the WTRU 102 may include any subcombination of the foregoing elements while remaining consistent with an embodiment.

[0020] 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 functionality 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 should be understood that the processor 118 and the transceiver 120 may be integrated together in an electronic package or chip.

[0021] 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 116. 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, for example, IR signals, UV signals, or visible light signals. In yet another embodiment, the transmit / receive element 122 may be configured to transmit and receive both RF signals and light signals. It should be understood that the transmit / receive element 122 may be configured to transmit and / or receive any combination of wireless signals.

[0022] 1B 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 116.

[0023] 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 noted above, the WTRU 102 may have multi-mode capabilities. Thus, the transceiver 120 may include multiple transceivers to enable the WTRU 102 to communicate via multiple RATs, such as, for example, UTRA and IEEE 802.11.

[0024] 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 random access memory (RAM), read-only memory (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).

[0025] 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.

[0026] 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 base stations (e.g., base stations 114a, 114b) over the air interface 116 and / or determine its location based on the timing of signals received from two or more nearby base stations. It should be understood that the WTRU 102 may acquire location information by way of any suitable location-determination method while remaining consistent with an embodiment.

[0027] Additionally, the processor 118 may 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 (e-compass), a satellite transceiver, a digital camera (for photos or videos), a universal serial bus (USB) port, a vibration device, a television transceiver, 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.

[0028] 1C is a system diagram of the RAN 104 and the core network 106 according to one embodiment. As noted above, the RAN 104 may use E-UTRA radio technology and communicate with the WTRUs 102a, 102b, 102c over the air interface 116. The RAN 104 may also communicate with the core network 106.

[0029] While the RAN 104 includes evolved Node Bs 140a, 140b, and 140c, it should be understood that the RAN 104 may include any number of evolved Node Bs while remaining consistent with an embodiment. The evolved Node Bs 140a, 140b, and 140c may each include one or more transceivers for communicating with the WTRUs 102a, 102b, and 102c over the air interface 116. In an embodiment, the evolved Node Bs 140a, 140b, and 140c may implement MIMO technology. Thus, for example, the evolved Node B 140a may use multiple antennas to transmit wireless signals to and receive wireless signals from the WTRU 102a.

[0030] Each of the evolved Node Bs 140a, 140b, 140c 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. 1C, the evolved Node Bs 140a, 140b, 140c may communicate with one another over an X2 interface.

[0031] 1C may include a mobility management gateway (MME) 142, a serving gateway 144, and a packet data network (PDN) gateway 146. Although each of the foregoing elements is shown as part of the core network 106, it should be understood that any one of these elements may be owned and / or operated by an entity other than the core network operator.

[0032] The MME 142 may be connected to each of the evolved Node-Bs 140a, 140b, 140c in the RAN 104 via an S1 interface and may act as a control node. For example, the MME 142 may be responsible for authenticating users of the WTRUs 102a, 102b, 102c, activating / deactivating bearers, selecting a particular serving gateway during initial attach of the WTRUs 102a, 102b, 102c, etc. The MME 142 may also provide a control plane function for switching between the RAN 104 and other RANs (not shown) that use other radio technologies such as GSM or W-CDMA.

[0033] The serving gateway 144 may be connected to each of the evolved Node Bs 140a, 140b, 140c in the RAN 104 via an S1 interface. The serving gateway 144 may generally route and forward user data packets to / from the WTRUs 102a, 102b, 102c. The serving gateway 144 may also perform other functions such as anchoring the user plane during inter-evolved Node B handovers, triggering paging when downlink data is available for the WTRUs 102a, 102b, 102c, managing and storing the context of the WTRUs 102a, 102b, 102c, etc.

[0034] The serving gateway 144 may also be connected to a PDN gateway 146, which 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.

[0035] The core network 106 may facilitate communication with other networks. For example, the core network 106 may provide the WTRUs 102a, 102b, 102c with access to circuit-switched networks, such as the PSTN 108, and may facilitate communication between the WTRUs 102a, 102b, 102c and traditional landline communication devices. For example, the core network 106 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 106 and the PSTN 108. Additionally, the core network 106 may provide the WTRUs 102a, 102b, 102c with access to networks 112, which may include other wired or wireless networks owned and / or operated by other service providers.

[0036] Additionally, the other network 112 may be connected to an IEEE 802.11-based wireless local area network (WLAN) 160. The WLAN 160 may include an access router 165. The access router may include a gateway function. The access router 165 may communicate with multiple access points (APs) 170a, 170b. Communication between the access router 165 and the APs 170a, 170b may be via wired Ethernet (IEEE 802.3 standard) or any type of wireless communication protocol. The AP 170a communicates wirelessly with the WTRU 102d over the air interface.

[0037] A shortened transmission time interval (sTTI) may be used to reduce latency. Physical channels designed based on a normal one TTI (nTTI) length (e.g., 1 ms) may not be optimized or may not function properly for shorter TTI lengths (e.g., one or several symbols in duration). For example, shortening the TTI of a control channel (e.g., a downlink (DL) control channel) or reducing the number of symbols available for the control channel may affect the performance of the channel. Redesign of one or more channels may be required to reduce the performance impact that a shortened TTI may cause.

[0038] Furthermore, the rules for control channel monitoring are designed for a certain level of blind decoding complexity and battery consumption for a specific TTI length. Shortening the TTI by a factor of N increases the number of blind decodes by a factor of N if the same rules are used. A mechanism may be needed to reduce the impact on blind decoding complexity and battery consumption that TTI shortening can cause.

[0039] The terms low latency transmission, reduced latency transmission, and sTTI transmission may be used interchangeably. Reduced latency transmission may use reduced TTI or sTTI. The terms reduced TTI, shortened TTI, sTTI, and rTTI may be used interchangeably. The terms TTI and TTI length may be used interchangeably. A shortened TTI length may refer to a TTI length shorter than another TTI length, which may be a typical regular nTTI or regular TTI length, such as 1 ms or 14 Orthogonal Frequency Division Multiplexing (OFDM) symbols. Regular (e.g., regular or legacy) transmission may use nTTI. The terms typical, regular, regular, and legacy may be used interchangeably. A shortened TTI length may be defined by the number of OFDM symbols Ns, where Ns may be less than the number of OFDM symbols for nTTI (e.g., Ns<14).

[0040] Time, frequency, and / or spatial resources may be configured, predefined, assigned, or indicated as resources for sTTI transmission and / or reception. Resources for sTTI transmission, sTTI resources, sTTI PRBs, sTTI subframes, sTTI symbols, sTTI REs, and sTTI antenna ports may be used interchangeably herein.

[0041] A time resource may include, but is not limited to, one or more OFDM symbols, one or more SC-FDMA symbols, one or more time slots, one or more subframes, one or more radio frames, and / or one or more time samples. A frequency resource may include, but is not limited to, one or more subcarriers, one or more PRBs, and / or one or more component carriers. A spatial resource may include, but is not limited to, one or more antenna ports, one or more reference signals, one or more cells, one or more physical cell IDs (PCIDs), and / or one or more virtual cell IDs (VCIDs).

[0042] FIG. 2 shows an example 200 of conventional hybrid automatic repeat request (HARQ) 210 for nTTI and HARQ 220 for reduced transmission time interval (sTTI). In one embodiment, the sTTI length may be between one symbol and one time slot, which may be seven symbols. As shown in FIG. 2, the sTTI may require less processing time and may provide a reduced hybrid automatic repeat request (HARQ) round trip time (RTT). An nTTI length of 1 ms may be too long to meet the needs of low-latency communications, such as machine-type communications, alarm reporting, automotive safety, factory process control, gaming, and voice over LTE (VoLTE). The scope of reduced latency may include physical channel design using reduced TTI for PDCCH, PDSCH, PUSCH, and PUCCH, reference signal design for reduced TTI physical channel demodulation, and HARQ operation using sTTI.

[0043] One or more components may contribute to the total end-to-end delay for a connected WTRU. These components may include, for example, one or more of scheduling grant acquisition time, TTI, processing time, and hybrid RTT. Transmission of requests, grants, HARQ feedback, and / or data may be made according to the timing of blocks or chunks, e.g., subframes, which may have a fixed or known duration (e.g., 1 ms). This duration may be referred to as the TTI. Processing time may be or include the time needed or used to process (e.g., encode and / or decode) data and / or control signaling or information. This may be done, for example, at or by the WTRU and / or eNB. Data processing time may be proportional to the TTI and / or transport block (TB) size of the data.

[0044] A downlink (DL) control channel may be mapped to at least a portion of a subframe. For example, the DL control channel may be located within (e.g., transmitted within) a set of OFDM symbols of a subframe, such as the first 1-3 or first 2-4 OFDM symbols of a subframe. The range of OFDM symbols that may be used (e.g., 1-3 or 2-4) may be based on the system bandwidth. The DL control channel may be located within one or more subframes. In one embodiment, the DL control channel may be located within every subframe.

[0045] A DL control channel for sTTI resource (e.g., sPDCCH) scheduling is required. Figure 3 shows an example of using a legacy EPDCCH for sTTI resource scheduling. In Figure 3, a subframe includes a PDCCH region at the beginning of the subframe. The subframe also includes an EPDCCH region that occurs in the symbols after the PDCCH over a portion of the bandwidth. The subframe also includes six sPDSCH regions that occur over a portion of the bandwidth allocated for sTTI frequency resources. Each sPDSCH region has a duration of one sTTI.

[0046] As shown in FIG. 3, using a legacy PDCCH for sTTI resource scheduling may increase latency depending on the sTTI resource location within a subframe. Also, using a legacy EPDCCH for sTTI resource scheduling may not reduce latency because the WTRU may need to wait until the end of the subframe to decode the EPDCCH. If an sPDCCH is located within each sTTI resource, the complexity of blind decoding within a time window (e.g., 1 ms) may increase due to an additional sPDCCH blind decoding operation at the beginning of the legacy EPDCCH.

[0047] The number of symbols (e.g., 1 to 3 or 2 to 4) that may be used for DL ​​control channels in a subframe may be determined according to control channel overhead. The control channel overhead may be, for example, the amount of control information that is in or transmitted in a subframe. The number of symbols that may be used may be different in different subframes. For example, with downlink control channel overhead, dynamic resource allocation may enable efficient downlink resource utilization, which may result in higher system throughput. DL control channels that may be transmitted in a subframe may include one or more of a physical control format indicator channel (PCFICH), a physical hybrid ARQ indicator channel (PHICH), and a physical downlink control channel (PDCCH).

[0048] A DL control channel resource unit may be defined as one or more resource elements (REs), which may be contiguous in the frequency domain. In one embodiment, a DL control channel resource unit may include four REs. A DL control channel resource element may be referred to as a resource element group (REG).

[0049] Referring now to Figures 4 and 5, examples of REGs are shown. Figures 4 and 5 show exemplary definitions of REGs by the number of cell-specific reference signals (CRSs), which may be CRS ports. Figure 4 shows the REG definition in a downlink control channel region with 2-Tx cell-specific reference signals (CRSs), shown as RS0 and RS1. Figure 5 shows the REG definition in a downlink control channel region with 4-Tx CRSs, shown as RS0, RS1, RS2, and RS3. When a CRS is located in the same OFDM symbol as a DL control channel, the DL control channel REG may be composed of consecutive REs (e.g., 4 REs) with the exception of REs containing CRSs, which may be skipped. In these examples, three symbols are used for the DL control channel, but other configurations are possible. For example, the set of symbols that may be used for the DL control channel in a subframe may be referred to herein as a DL control channel region.

[0050] The PCFICH may be transmitted within an OFDM symbol (e.g., the first OFDM symbol or symbol 0) in one or more subframes, which may include every subframe. The PCFICH may indicate the number of OFDM symbols that may be used for the downlink control channel in a subframe. Subframe-level dynamic downlink control channel resource allocation may be implemented using the PCFICH. The WTRU may detect a control format indicator (CFI) from the PCFICH. The downlink control channel region (e.g., the size of the DL control channel region) may be defined within a subframe according to the CFI value. Table 1 shows an example of a CFI codeword that may be detected from the PCFICH. Table 2 shows an example of downlink control channel resource allocation according to one or more parameters, such as a CFI value, subframe type, frame structure, and system bandwidth. The system bandwidth in DL is determined by the DL

[0051]

number

[0052] [Table 1]

[0053] [Table 2]

[0054] The PCFICH may not be transmitted and / or used in some subframes, e.g., in subframes that do not support a PDSCH or in subframes where a PDSCH or another DL channel begins at a known symbol or time position. The WTRU may not attempt to detect the PCFICH in subframes in which the PCFICH may not be transmitted and / or used.

[0055] Several REGs (e.g., 4 REGs) may be used for PCFICH transmission, for example, in the first OFDM symbol in a subframe. These REGs may be distributed uniformly across at least a portion of the system bandwidth (e.g., the DL system bandwidth) or across the entire system bandwidth. This distribution may exploit frequency diversity gain.

[0056] Referring now to Figure 6, the diagram illustrates allocation of PCFICH REGs by physical cell ID (PCI). The starting point (e.g., in frequency) of PCFICH transmission may differ according to PCI. Frequency shifting of PCFICH based on cell ID may improve PCFICH detection performance, for example, by avoiding PCFICH among multiple neighboring cells.

[0057] The WTRU may begin downlink control channel detection in a subframe by decoding the PCFICH to determine the number of OFDM symbols for the downlink control channel in that subframe. A PCFICH detection error may result in the loss of at least one of a downlink grant, an uplink grant, and a PHICH reception, for example, since the downlink control resource may be defined by the PCFICH.

[0058] The PHICH may be used to transmit an ACK or NACK corresponding to a PUSCH transmitted in an uplink subframe. The PHICH may be transmitted, for example, distributed across at least a portion of the system bandwidth (e.g., DL system bandwidth) and at least some of the OFDM symbols in the downlink control channel region. The number of OFDM symbols that may be used for the PHICH may be referred to as the PHICH duration. The PHICH duration may be configurable, for example, by higher layer signaling or broadcast signaling (e.g., in the MIB or SIB). The PHICH resource location (e.g., in frequency) may vary according to the PCI and / or the PHICH duration.

[0059] Referring now to FIG. 7, a diagram illustrating PCFICH and PHICH REG according to PCI is shown. Multiple PHICH groups may be defined or used in a cell. A PHICH group may include multiple PHICHs that have or may use orthogonal sequences. The PHICH that may be destined for a WTRU may be dynamically defined with resource information provided, for example, in an uplink grant. The uplink grant may be for a PUSCH, where the PHICH may include an ACK or NACK. The resource information may be based on the lowest PRB index.

[0060]

number

[0061]

number

[0062]

number

[0063] Exemplary PHICH Index Pairs

[0064]

number

[0065]

number

[0066]

number

[0067]

number

[0068]

number

[0069]

number

[0070] The orthogonal sequence may be determined according to the spreading factor. An example is shown in Table 3.

[0071] [Table 3]

[0072] The HARQ indicator (HI) may be coded, for example, as shown in Table 4. For a positive acknowledgment, HI may be equal to 1, and for a negative acknowledgment, HI may be equal to 0.

[0073] [Table 4]

[0074] A PDCCH (or PDCCH candidate) may consist of one or more control channel element (CCE) resources, which may be contiguous. One CCE may contain several REGs, such as 9 REGs. The number of available CCEs (N CCE ) is, for example, for the example of 9REG per CCE, N CCE =[N REG / 9], where N REG may be the number of REGs that are not associated with PCFICH or PHICH. Table 5 shows examples of PDCCH formats by number of CCEs, where the CCEs may be contiguous.

[0075] [Table 5]

[0076] A WTRU may monitor or may need to monitor one or more PDCCH candidates to decode or successfully decode a PDCCH format, such as, for example, a DL control information (DCI) format that may be directed to the WTRU. The WTRU may decode (e.g., blindly decode) or attempt to decode one or more candidates at each of one or more aggregation levels. The set of PDCCH candidates that the WTRU may monitor, decode (e.g., blindly), attempt to decode, or may need to monitor, decode (e.g., blindly), or attempt to decode may be a search space. Table 6 shows an example of a search space and associated PDCCH candidates.

[0077] [Table 6]

[0078] The number of CCEs may be different for different PDCCH formats, e.g., as shown in Table 5. The aggregation level may correspond, for example, to the number of CCEs in the PDCCH format. A set of aggregation levels (e.g., {1, 2, 4, 8}) may be supported or used within a WTRU-specific search space. Another set of aggregation levels (e.g., {4, 8}) may be supported or used within a common search space. The WTRU-specific search space may be a search space configured for a WTRU that the WTRU may monitor. The common search space may be a search space configured for a cell, e.g., in broadcast signaling, that one or more (e.g., all) WTRUs in the cell may monitor.

[0079] Search space at aggregation level L

[0080]

number

[0081]

number

[0082]

number

[0083] WTRU-specific search space at aggregation level L

[0084]

number

[0085]

number

[0086] The value of m′ may be defined according to one or more of a search space type and a configuration for using cross-carrier scheduling. The configuration for using cross-carrier scheduling may be indicated by a configuration with a carrier indicator field. When cross-carrier scheduling is not used or configured for a serving cell, a control channel for the serving cell (e.g., carrying a grant or ACK / NACK) may be transmitted and / or monitored, for example, on the DL control channel region of that serving cell. When cross-carrier scheduling is used or configured for a serving cell, a control channel for the serving cell (e.g., carrying a grant or ACK / NACK) may be transmitted and / or monitored, for example, on the DL control channel region of another serving cell.

[0087] For example, for a common search space, m' may be defined as m' = m. For a WTRU-specific search space and for the serving cell whose PDCCH is monitored, m' may be defined as m' = m + M. (L) n CI This may apply when the monitoring WTRU is configured with, for example, a carrier indicator field for the serving cell to which the PDCCH candidate applies. CI The value of may be a carrier indicator field value. For a WTRU-specific search space and for the serving cell for which the PDCCH is monitored, m' may be defined as m' = m. This may be applicable when the monitoring WTRU is configured with, for example, a carrier indicator field for the serving cell to which the PDCCH candidate applies.

[0088] Resource element (RE) muting can be used to avoid signal collisions. For muted REs, puncturing or rate matching can be used, for example, from the perspective of the coding chain. When puncturing is used, the signal that can be mapped to the punctured RE may not be transmitted or may be transmitted with zero power within that RE. When rate matching is used, the mapping of the signal to the REs may avoid mapping to some REs, whereby other signals may not be transmitted.

[0089] In one example, an N-bit coded bit sequence for a certain channel, for example, (c1,..., c N ) can be the output of a channel encoder that takes a payload or information as input. The channel encoder can be any channel code, including, for example, a turbo code, a convolutional code, or a Reed-Muller code. The coded bit sequence can be the input to a mapper.

[0090] An M-symbol modulation symbol sequence, for example, (x1,..., x M ) can be the output of a mapper that modulates the coded bit sequence with a certain modulation scheme (for example, BPSK, QPSK, 16QAM, or 64QAM). Depending on the modulation scheme used, the modulation symbol sequence length M can be less than or equal to N.

[0091] The modulation symbol sequence can be mapped to a set of REs for the channel according to a predefined order. For example, x1,..., x M can be mapped to M REs, which can be used for the channel in a predefined order. For example, if the k-th (where k < M) RE is muted due to a collision, puncturing will be performed on the modulation symbol x kThe rate-matching may mean that the mapping skips the muted REs and that fewer modulation symbols may be mapped. For one rate-matched RE, M-1 modulation symbols may be mapped and transmitted. For example, x1,...,x M-1 may be transmitted, and one last modulation symbol may not be transmitted due to the muting of the kth RE. Puncturing may result in losing coded bits in the position of the muted RE, while rate matching may result in losing coded bits from the last coded bit.

[0092] Hereinafter, RE muting with puncturing may be referred to as “RE puncturing,” and RE muting with rate matching may be referred to as “RE rate matching.” The term “RE muting” may include RE puncturing and / or RE rate matching.

[0093] In conventional LTE systems, RE muting may be implemented to avoid collisions between different types of signals in the same direction. For example, in DL, PDSCH REs may be muted to avoid collisions with CSI-RS, and PRS REs may be muted to avoid collisions with PSS and SSS. In UL, PUSCH and PUCCH may be shortened to avoid collisions with SRS in the UL.

[0094] In one embodiment, one or more sTTI resource types may be used. The sTTI resource type may be associated with and / or determined based on one or more parameters. One parameter may be a frequency location, including at least one of a PRB location, a component carrier location, a frequency band, and a subcarrier location. Another parameter may be an amount of frequency resources used, including at least one of a number of PRBs, a number of subcarriers, a number of REs, and a number of component carriers. Another parameter may be a time location, including at least one of a DL or UL symbol location within a subframe, a starting DL or UL symbol location within a subframe, a number of subframes or a starting subframe, and a SFN number.

[0095] Another parameter may be an amount of time resources including at least one of a number of DL symbols (e.g., OFDMA symbols) or UL symbols (e.g., SC-FDMA symbols), a number of slots, a number of subframes, a number of time samples, and a number of radio frames. The amount of time resources may be a function of or determined based on the number of sTTIs available within a subframe. Another parameter may be spatial resources including at least one of an associated antenna port number or number, a reference signal type (e.g., DM-RS or CRS), an associated physical cell ID, and an associated virtual cell ID.

[0096] One or more sTTI resource types may be used, configured, allocated, and / or indicated for a period of time. This period may be one or more symbols, subframes, radio frames, or slots. This period may be referred to herein as an sTTI time window. The terms sTTI period, sTTI window, sTTI resource type time window, and sTTI time window may be used interchangeably. The sTTI time window may be one or more of an sTTI period, a regular TTI period, and / or a subframe.

[0097] An sTTI resource type may refer to resources for an sTTI physical downlink control channel (sPDCCH), an sTTI physical downlink shared data channel (sPDSCH), an sTTI physical uplink shared data channel (sPUSCH), and / or an sTTI physical uplink control channel (sPUCCH). The terms sTTI resource type and sTTI type may be used interchangeably. Channels or signals described herein may be represented by abbreviations beginning with s, such as sPDCCH, sPDSCH, sPUSCH, and sPUCCH. In the examples and embodiments described herein, these prefixes may be used to represent abbreviated TTIs or sTTIs.

[0098] 8 illustrates multiple sTTI resource types configured within a subframe. More specifically, FIG. 8 illustrates an example of a resource configuration with multiple sTTI resource types within a subframe, where non-overlapping frequencies may be used for different sTTI resource types. A first sTTI resource type and a second sTTI resource type may be located within non-overlapping sets of PRBs.

[0099] As described herein, the sTTI resource type may be determined, configured, or predefined for one or more sTTI physical channels (e.g., per sTTI physical channel). For example, a first sTTI resource type (e.g., sTTI type 0) may be used for the sPDCCH, and a second sTTI resource type (e.g., sTTI type 1) may be used for the sPDSCH. In another example, the first sTTI resource type may be used for the downlink physical channel, and the second sTTI resource type may be used for the uplink physical channel. In another example, the first sTTI resource type may be used for the physical shared data channel (e.g., sPDSCH and / or sPUSCH), and the second sTTI resource type may be used for the physical control channel (e.g., sPDCCH and / or sPUCCH).

[0100] In another example, a first sTTI resource type may be used for one or more sTTI physical channels using a first sTTI (e.g., an sPDSCH using N symbols, where N may be 2), and a second sTTI resource type may be used for one or more sTTI physical channels using a second sTTI (e.g., an sPDSCH using M symbols, where M may be 7). The sTTI physical channels using the first and second sTTI resource types may be transmitted and / or received in the same subframe. The sTTI physical channels using the first and second sTTI resource types may be directed to different WTRUs (or to the same WTRU) and / or received by different WTRUs (or the same WTRU).

[0101] While Figure 8 illustrates an example in which sTTI resources overlap in time but do not overlap in frequency, it should be noted that there are many different possible configurations for allocating sTTI resources within a subframe. For example, one or more sTTI resource types may be configured within a subframe, and those one or more sTTI resource types may be non-overlapping in time, frequency, and space resources. In another example, one or more sTTI resource types may be configured within a subframe, and those one or more sTTI resource types may fully or partially overlap in time, frequency, and / or space resources. The terms resource overlapping and resource sharing may be used interchangeably. Two or more sTTI resource types may fully or partially overlap in a first resource (e.g., time, frequency, or space), while not overlapping in a second resource (e.g., time, frequency, or space), and the first and second resources may be different. Two or more sTTI resource types may fully or partially overlap in time and / or frequency resources, while different spatial resources may be used for the two or more sTTI resource types. Two or more sTTI resource types may fully or partially overlap in time, while different frequency resources may be used for the two or more sTTI resource types. Two or more sTTI resource types may fully or partially overlap in frequency, while different time resources may be used for the two or more sTTI resource types. Two or more sTTI resource types may be assigned to any other combination of overlapping and non-overlapping time, frequency, and time resources within a subframe.

[0102] One or more of the following parameters may apply to the set of PRBs: One or more PRB allocation types may be used to determine the set of PRBs assigned to an sTTI resource type: A first PRB allocation type may use localized PRBs (e.g., contiguous PRBs) to allocate the set of PRBs. A second PRB allocation type may use distributed PRBs (e.g., non-contiguous PRBs) to allocate the set of PRBs. The PRB allocation type (or PRB locations for the set of PRBs) may be defined (e.g., predefined) and / or determined based on the sTTI resource type. The PRB allocation type (or PRB locations for the set of PRBs) may be configured via higher layer signaling. The PRB allocation type may be configured for one or each of the sTTI resource types, or may be configured in a cell-specific or WTRU-specific manner. The PRB allocation type (or PRB locations for the set of PRBs) may be dynamically indicated in one or each of the sTTI time windows.

[0103] One or more sTTI resources having the same sTTI resource type may be used, for example, in an sTTI, an sTTI window, a regular TTI, and / or a subframe. For example, a first sTTI resource may be configured at a first frequency location, and a second sTTI resource may be configured at a second frequency location. The first frequency location and the second frequency location may not overlap in the frequency domain. The first sTTI resource and the second sTTI resource may be of the same sTTI resource type. For example, one or more of the amount of time resources, the amount of frequency resources, and the amount of spatial resources may be the same.

[0104] An sTTI resource type may refer to resources for multiple sTTI physical channels, such as an sPDCCH and an sPDSCH, or an sPDSCH and an sPUCCH, where the resources of these multiple channels may not overlap or may not fully overlap, but may be related. For example, an sTTI resource type may be used for an sPDCCH and an sPDSCH, where these channels may use the same frequency resources, but the sPDSCH may be after the sPDCCH in time (e.g., by a configured, predetermined, or known relationship).

[0105] The WTRU may transmit, receive, monitor, attempt to receive, or attempt to decode one or more sTTIs within the sTTI time window. The WTRU may transmit, receive, monitor, attempt to receive, or attempt to decode one or more sTTI resources and / or resource types within the sTTI time window.

[0106] The following description may include sTTI resource presence and / or sTTI resource type indication. In one embodiment, the WTRU may receive or attempt to decode an indication for sTTI resource presence and / or one or more sTTI resource types during an sTTI time window. The WTRU may receive or attempt to decode this indication within a control channel region that may be located within the sTTI time window. This indicator may be referred to as an sTTI indicator.

[0107] An sTTI indicator may be or include an indicator for sTTI resource presence or an indicator for sTTI resource type. Indicator and indication may be used interchangeably. One or more sTTI indicators may be used for one or more sTTI resources. For example, if multiple sTTI resources are configured or used within an sTTI time window, the presence of the sTTI resource may be indicated by the associated sTTI indicator. The multiple sTTI resources may be of the same sTTI resource type or different sTTI resource types. The sTTI indicator may be an explicit indication or may be based on an event, signaling format, timing, etc.

[0108] One or more control regions (e.g., control channel regions) may be located within the sTTI time window, and the WTRU may receive or attempt to decode at least one sTTI indicator in at least one of the control regions. A control region may include a set of time and / or frequency resources. A control region may carry control information and / or one or more control channels. The terms control region and control channel region may be used interchangeably. A control region that may carry an sTTI indicator may be a control region (e.g., a first control region) located at the beginning of a period that may be the sTTI time window.

[0109] 9 and 10 are diagrams illustrating control region locations for sTTI indicators. In FIG. 9, a PDCCH region 910 is located at the beginning of a regular TTI or subframe. The PDCCH region 910 may include an indication 940 of the presence and / or resource type and location of the sTTI resources within the subframe. In the example of FIG. 9, a first frequency region includes sTTI type 1 resources 920, and a second frequency region includes sTTI type 0 resources 930. The sTTI type 1 resources 920 and the sTTI type 0 resources 930 overlap in time. In this example, the PDCCH region 910 may include an indication 940 of the presence and / or resource type and location of each sTTI region 920, 930.

[0110] Figure 10 shows a subframe that includes a PDCCH region 1010 at the beginning of the subframe. The control region may be the first sPDCCH region 1025 within or among multiple sPDCCH regions 1035, 1045 as shown in Figure 10. The control region may be the first sPDCCH region within or among multiple sPDCCH regions (e.g., all sPDCCH regions) within a period that may be an sTTI time window (e.g., a regular TTI or subframe).

[0111] The control region that may carry the sTTI indicator may be a PDCCH region (e.g., a legacy PDCCH control region) that may be located in the first N OFDM symbols of a subframe. The value of N may be a defined, determined, or configured value (e.g., N=2), for example, when a subframe includes one or more sTTI resources. The value of N may be dynamically indicated from the PCFICH. The PCFICH may be located within the control region (e.g., the first control region) that may carry the sTTI indicator.

[0112] The control region that may carry the sTTI indicator may be the first sPDCCH in the sTTI time window. For example, M sTTIs may be used, configured, or available within the sTTI time window. At least one of the M sTTIs may include an associated sPDCCH. The WTRU may receive, or attempt to receive, at least one sTTI indicator in the sPDCCH in the first sTTI of the M sTTIs.

[0113] The WTRU may monitor, attempt to receive, receive, or attempt to receive an sTTI indicator in at least one control region within the sTTI time window. The WTRU may use the sTTI indicator to determine the presence of at least one sTTI resource within the sTTI time window or another period. An example period may be when the WTRU successfully receives or successfully determines the presence of an sTTI indicator. Another possible period may be a later sTTI time window.

[0114] The WTRU may determine the presence of at least one sTTI resource within the sTTI time window based on at least one of the presence, value, or content of an sTTI indicator, for example, that may be received within the sTTI time window or another period. An example of another period may be a previous (e.g., immediately preceding) or earlier sTTI time window. If an sTTI resource is configured within the sTTI time window, the WTRU may attempt to receive one or more sPDCCHs within that sTTI resource. If an sTTI resource is not configured, the WTRU may not attempt to receive at least some sTTI physical channels within the sTTI time window, or other physical channels that may be within the sTTI time window. Other physical channels may refer to physical channels different from those for which the WTRU monitored, attempted to receive, or received the sTTI indicator. A control region that may carry an sTTI indicator may be part of or included in an sTTI resource (or resource type) for which the sTTI indicator may indicate presence (or lack of presence).

[0115] The presence of an sTTI resource or sTTI resource type may be determined based on one or more of the following parameters: system parameters, which may include one or more of the system bandwidth, physical cell ID, number of slots, number of subframes, and number of SFNs; WTRU-specific parameters, which may include one or more of the WTRU-IDs (e.g., C-RNTI, IMSI, sTMSI, etc.); and configuration information for the sTTI, which may be signaled in higher layer signaling (e.g., MIB, SIB, or WTRU-specific RRC signaling).

[0116] The following description may include sTTI resource configuration mechanisms: sTTI resources may be configured and / or used; One or more sTTI resources may be configured via higher layer signaling; sTTI resources may be configured with a time / frequency location; sTTI resources may refer to resources that may carry at least one sTTI physical channel (e.g., sPDCCH, sPDSCH, sPUCCH, sPUSCH).

[0117] One or more sTTI resources may be configured via a DCI. The DCI, which may configure one or more sTTI resources, may be monitored by the WTRU, for example, periodically or at configured or predetermined times. A DCI scrambled with an RNTI associated with at least one sTTI transmission may be used. This DCI may be referred to, for example, as an sTTI-RNTI. For example, the sTTI-RNTI scrambled DCI may be monitored within a subframe, a set of subframes, an SFN, and / or a set of SFNs (e.g., a set of SFNs or a set of SFNs that meet certain criteria).

[0118] The DCI may configure one or more sTTI resources. For example, the DCI scrambled with the sTTI-RNTI may be transmitted (e.g., by a base station) and / or monitored by a WTRU in the first subframe of each radio frame. A set of subframes or SFNs on which the sTTI-RNTI is to be monitored may be configured. The DCI scrambled with the sTTI-RNTI may be transmitted (e.g., by a base station) and / or monitored by a WTRU in, for example, a set of subframes or SFNs that may be configured and / or used for the sTTI-RNTI.

[0119] The sTTI resources may be configured by the base station. The WTRU may receive the sTTI resource configuration, for example, from the base station. The WTRU may use (e.g., transmit, receive, or attempt to receive within) the sTTI resources, which may be configured by the base station or other network entity.

[0120] A base station may transmit within an sTTI resource, e.g., in the DL. A WTRU may receive or attempt to receive a transmission within an sTTI resource, e.g., in the DL. A WTRU may transmit within an sTTI resource, e.g., in the UL. A base station may receive or attempt to receive a transmission within an sTTI resource, e.g., in the UL.

[0121] The sTTI indicator may be based on, transmitted on, or associated with a PHICH resource. In one embodiment, one or more PHICH resources may be located within a control region, such as a PDCCH region or an sPDCCH region, and such region may carry or be used to provide an sTTI indicator. For example, one or more sTTI resources may be configured, and the presence of the sTTI resource may be indicated within an sTTI time window by the sTTI indicator. One or more PHICH resources (e.g., resources that may be configured, reserved, or used for the PHICH) may be used to carry at least one sTTI indicator. One or more PHICH resources may be configured and / or used for the sTTI indicator.

[0122] PHICH resources are PHICH Group Index

[0123]

number

[0124]

number

[0125] [Table 7]

[0126] Table 8 shows an example of an sTTI indicator that uses one or more PHICH resources for sTTI resource presence and sTTI resource type indication.

[0127] [Table 8]

[0128] Note that Tables 7 and 8 provide non-limiting examples of using PHICH resources to indicate sTTI resource presence and / or sTTI resource type.

[0129] Transmission and / or reception of the indicated HARQ indicator (HI) codeword using the indicated PHICH sequence in the indicated PHICH position by the indicated PHICH group may correspond to the indicated sTTI configuration (e.g., within the sTTI window of PHICH transmission and / or reception).

[0130] When using PHICH resources to carry sTTI indicators, one or more of the following parameters may apply: The sTTI indicator for the first sTTI resource and the sTTI indicator for the second sTTI resource may be in different PHICH groups and / or use different PHICH sequences. The sTTI indicator for the first sTTI resource type and the sTTI indicator for the second sTTI resource type may be in different PHICH groups and / or use different PHICH sequences. An HI codeword may be used to indicate the presence of an sTTI resource or an sTTI resource type. An even or odd PHICH sequence may be used for the sTTI indicator. A PHICH sequence with maximum distance (e.g., indexes 0 and 4 for normal CP) or minimum distance (e.g., two consecutive sequence numbers) may be used to indicate the presence of an sTTI resource.

[0131] Based on receiving an sTTI indicator using a PHICH resource, the WTRU may determine that an sTTI resource or resource type exists within an sTTI window, e.g., the sTTI window in which the sTTI indicator or PHICH resource was received. When the WTRU determines that an sTTI resource exists, the WTRU may monitor, attempt to receive, and / or receive the sTTI resource. When the WTRU determines that an sTTI resource of a certain sTTI resource type exists, the WTRU may monitor, attempt to receive, and / or receive the sTTI resource according to the sTTI resource type.

[0132] One or more PHICH resources that may be used for at least one sTTI indicator may be determined based on system parameters that may include one or more of the following parameters: system bandwidth, PHICH configuration, physical cell ID, number of subframes, and / or number of SFNs; WTRU-specific parameters that may include one or more of a WTRU-ID (e.g., C-RNTI, full or partial IMSI, sTMSI, etc.); and configuration information for the sTTI that may be signaled in higher layer signaling (e.g., MIB, SIB, or WTRU-specific RRC signaling). The PHICH resources that may carry the sTTI indicator may be part of or included in the sTTI resources (or resource types) for which the sTTI indicator may indicate presence (or lack of presence).

[0133] A signal may be used to carry the sTTI indicator. The term sTTI indicator signal may be used to refer to a signal that may be used as an sTTI indicator. The sTTI indicator signal may be a predefined signal, a configured signal, or a known signal. The sTTI indicator signal may be associated with one or more sTTI resources and / or sTTI resource types. The presence of an sTTI indicator signal may indicate the presence of an associated sTTI resource and / or sTTI resource type within an sTTI window, such as the sTTI window in which the sTTI indicator signal resides.

[0134] The sTTI indicator signal may be transmitted at a known location, e.g., a predefined signal may be transmitted at a known location, and the presence of the predefined signal (e.g., the sTTI indicator signal) may determine the presence of the sTTI resource.

[0135] The sTTI indicator signal is used to indicate the Nth period of the sTTI time window or sTTI resource. STTI symbols (e.g., the first N STTIsymbol). STTI can be any positive integer, including 1. STTI N may be predefined or configured via higher layer signaling. STTI N may be determined as a function of one or more of the following parameters: the time resource amount of the associated sTTI resource, the sTTI window length, the number of subframes, the number of slots, and / or the SFN, as well as system parameters including the frame structure (e.g., TDD, FDD), the system bandwidth, and / or the physical or virtual cell ID. STTI may be dynamically indicated from an associated control channel (eg, legacy PDCCH).

[0136] The sTTI indicator signal may be a PCFICH. The sTTI indicator signal may be transmitted within an sPDCCH region (e.g., the first sPDCCH region) within the sTTI time window. The sTTI indicator signal may be a known sequence (e.g., a Zadov-Chu sequence, a PN sequence, or a Golay sequence).

[0137] The WTRU may attempt to receive, receive, decode, or attempt to decode an sTTI indicator signal to determine the presence of one or more sTTI resources. The WTRU may monitor, receive, attempt to receive, decode, and / or attempt to decode one or more sTTI resources (e.g., sTTI channels such as sPDCCH), for example, when the WTRU determines that one or more sTTI resources exist. The WTRU may monitor, receive, attempt to receive, decode, and / or attempt to decode one or more sTTI resources (e.g., sTTI channels such as sPDCCH) within the sTTI window of the sTTI indicator signal, for example, when the WTRU determines that one or more sTTI resources exist based on reception and / or decoding (e.g., successful reception and / or decoding) of an sTTI indicator signal.

[0138] The WTRU may skip receiving (e.g., not attempt to monitor, receive, and / or decode) an sTTI resource (e.g., sPDCCH and / or sPDSCH) if the WTRU determines that an sTTI resource (or additional sTTI resource) does not exist. The WTRU may skip receiving an sTTI resource within an sTTI window if the WTRU determines that an sTTI resource (or additional sTTI resource) does not exist within that sTTI window. The WTRU may determine that an sTTI resource (or additional sTTI resource) does not exist (e.g., within an sTTI window) if the WTRU does not detect, receive, or decode an sTTI indicator signal.

[0139] The WTRU may assume that no sPDCCH and / or sPDSCH is transmitted within an sTTI window in which the WTRU does not detect, receive, or decode an sTTI indicator or sTTI indicator signal within the sTTI window or the time corresponding to the sTTI window.

[0140] Receiving one or more sTTI resources when one or more sTTI resources exist may include at least one of monitoring an sPDCCH within the associated sTTI resource for downlink DCI (e.g., a DCI indicating a DL grant or other DL request or assignment) and / or uplink DCI (e.g., a DCI indicating a UL grant or other UL request or assignment), and receiving one or more sPDSCHs within the scheduled time, frequency, and / or space resources.

[0141] In another embodiment, a set of REGs in a control region (e.g., a PDCCH region or an sPDCCH region) that is within the sTTI time window may be reserved or used for the sTTI indicator signal. The set of REGs may be distributed across the system bandwidth or a portion of the system bandwidth. The set of REGs may be associated with a number of CCEs (e.g., a certain number of CCEs that may be configured and / or known). The set of REGs may be determined based on at least one of the following parameters: system parameters (e.g., physical or virtual cell ID, system bandwidth), sTTI resource type (e.g., time / frequency / spatial resources, sTTI length), and WTRU-specific parameters (e.g., WTRU-ID, C-RNTI).

[0142] A downlink control information (DCI) message may be used to configure sTTI resources. In one embodiment, a DCI may be used to indicate the presence of one or more sTTI resources. For example, a DCI may be used to indicate the presence of one or more sTTI resources within an sTTI time window. A DCI within an sTTI time window may be used to indicate the presence of one or more sTTI resources within the same sTTI time window or another time period, such as another sTTI window.

[0143] One or more sTTI resources may be configured via higher layer signaling. The presence of one or more sTTI resources (e.g., one or more of the configured sTTI resources) within the sTTI time window may be indicated within a DCI (e.g., a DCI within the sTTI time window or another time period, such as a previous sTTI time window). The DCI may be transmitted within the control region within the sTTI window. For example, the DCI may be transmitted within the legacy PDCCH region within the sTTI window. The DCI may be monitored within a common search space of the control region (e.g., the legacy PDCCH region). Alternatively, the DCI may be monitored within a set (e.g., a predetermined set or a configured set) of PDCCH resources (e.g., legacy PDCCH resources). For example, a predetermined or configured set of CCEs (e.g., CCEs #16-32) may be used. The DCI may be scrambled with an sTTI-specific RNTI (e.g., sTTI-RNTI). The DCI may indicate the presence of sTTI resources and / or associated sTTI resource types. The presence of sTTI resources may be determined based on the sTTI-specific RNTIs used. For example, one or more sTTI-specific RNTIs may be used to indicate the presence of one or more sTTI resources. Each sTTI resource may be associated with a specific sTTI-RNTI. A bitmap may be used within the DCI to indicate which sTTI resources are present within the sTTI time window.

[0144] The DCI may be used to configure sTTI resources within the sTTI time window. For example, time, frequency, and / or spatial resources for the sTTI resources may be indicated in the DCI.

[0145] A downlink control channel, referred to as an sPDCCH, may be associated with one or more sTTIs. The terms sPDCCH, downlink control channel for an sTTI, downlink control information for an sTTI, sTTI DCI, and sDCI may be used interchangeably.

[0146] An sPDCCH may be located within an sTTI resource. An sTTI resource may be or include at least one sPDCCH. An sPDCCH may be, or may be referred to as, an sTTI resource. An sPDCCH may be a portion of, or may be referred to as an sTTI resource. The terms sPDCCH resource, sPDCCH region, sPDCCH symbol, sPDCCH subcarrier, and sPDCCH REs may be used interchangeably.

[0147] An sPDCCH resource may be associated with one or more sTTIs. For example, an sPDCCH may be associated with one or more sPDSCHs located within sTTIs that may be the same or different from each other or the same or different from the sTTI of the sPDCCH. An sPDCCH may include scheduling information for the associated sPDSCH or sPDSCHs.

[0148] An sTTI may include at least one sPDCCH. An sTTI may include at least one sPDSCH that may be associated with an sPDCCH that may be included within the sTTI. For example, in an sTTI, a subset of the sTTI resources may be used for the sPDCCH, and the remaining portion of the sTTI resources may be used for the sPDSCH. A WTRU may monitor or attempt to decode an sPDCCH within the sTTI or sPDCCH region. An sPDCCH may include one or more scheduled sPDSCHs.

[0149] The WTRU may skip monitoring if it does not monitor the sPDCCH within resources (e.g., within an sTTI) where the sPDSCH may be scheduled. The WTRU may determine where the sPDSCH is scheduled (e.g., within an sTTI) based on reception of an sPDCCH including sPDSCH scheduling (e.g., for the sTTI). For example, two or more sTTIs, which may be of the same length or different lengths, may overlap. Each sTTI may include a subset of resources for the sPDCCH and a subset of resources for the sPDSCH. For each sTTI, the resources for the sPDCCH and sPDSCH may not overlap. The resources for the sPDSCH in a first sTTI may overlap with the sPDCCH resources in a second sTTI. If the sPDSCH resources are determined by the WTRU to be scheduled in the first sTTI, the WTRU may not monitor the sPDCCH in the sPDCCH resources in the second sTTI. This may be due to overlap with the sPDSCH resources scheduled in the first sTTI. The WTRU may monitor the sPDCCH in the sPDCCH resources in the second sTTI when the sPDCCH resources in the second sTTI do not overlap with the scheduled sPDSCH resources (e.g., in the first sTTI). The WTRU may determine that the sPDCCH resources in the second sTTI do not overlap with the scheduled sPDSCH resources.

[0150] An sTTI window may include one or more sTTIs, which may be overlapping or non-overlapping. The sTTIs within an sTTI window may be the same length or different lengths. A control channel (e.g., a PDCCH or sPDCCH) or control information (e.g., a DCI or sDCI) may indicate potential scheduling that may exist within the sTTI window (e.g., a regular TTI or subframe). The potential scheduling may be or may include at least one of the following parameters: number of sTTIs, number of sPDSCHs, number of sPDCCHs, number of sTTI control regions, and / or number of sPDCCH regions. The WTRU may monitor the sPDCCH in one or more sTTIs or one or more sPDCCH regions within the sTTI window. The WTRU may not monitor the sPDCCH within the sTTI window after receiving sPDSCH scheduling within or during the sTTI window. The WTRU may not monitor the sPDCCH within the sTTI window in resources that overlap with a scheduled sPDSCH, which may occur, for example, when the WTRU receives scheduling for the sPDSCH and / or determines that the sPDSCH is scheduled.

[0151] An sPDCCH (e.g., a DCI) may indicate several sPDSCHs, which may be in a set, such as {nl, n2, n3, n4}. This set may be configured, defined, and / or determined. The number of sPDSCHs (e.g., n2) may determine, for example, the number of sTTIs (e.g., consecutive sTTIs) that may be used for sPDSCH scheduling within an sTTI window. A WTRU may monitor an sPDCCH or sPDCCH region within an sTTI, for example, when the WTRU is not scheduled (e.g., within an sTTI window or within a resource that overlaps with an sPDCCH resource).

[0152] An sPDCCH (e.g., an sDCI) may indicate a set of sTTIs within an sTTI time window for scheduling an sPDSCH. For example, a bitmap may be used to indicate which sTTI resources or multiple sTTIs within the sTTI time window may carry an sPDCCH. An sPDCCH region within an sTTI may be used for sPDSCH transmission, for example, when an sPDSCH may be scheduled in a previous sTTI (e.g., by an sPDCCH in an sPDCCH region in a previous sTTI). An sPDCCH region that may be used for scheduling an sPUSCH may be reserved and / or not used for sPDSCH transmission. Note that a PDCCH may be used instead of an sPDCCH, and a DCI may be used instead of an sDCI.

[0153] 11 is a diagram illustrating an example of sPDCCH and sPDSCH association per sTTI. An sPDCCH may be located within each sTTI, and an associated sPDSCH may be scheduled from an sPDCCH located within the same sTTI.

[0154] 12 is a diagram illustrating multiple sPDCCH and sPDSCH associations. An sPDCCH may be associated with one or more sPDSCHs, and the number of sPDSCHs associated with an sPDCCH may be determined based on an sPDCCH cycle.

[0155] Figure 13 illustrates the use of a PHICH resource as an sTTI indicator. One or more sTTI resources may be configured via higher layer signaling. A WTRU may receive one or more sTTI indicators associated with one or more sTTI resources in a subframe. The WTRU may monitor an sPDCCH in one or more sTTI resources based on the configuration indicated from the sTTI indicator. The WTRU may receive an sPDSCH or transmit an sPUSCH based on scheduling information from the DCI in the sPDCCH.

[0156] An sPDCCH cycle may be the time between sPDCCH regions. An sPDCCH cycle may be a period during which sPDCCH regions may exist. An sPDCCH cycle may indicate the number and / or position (e.g., time position) of sPDCCH regions, for example, within an sTTI window (e.g., a regular TTI or subframe).

[0157] One or more of the following parameters may apply to the sPDCCH configuration: The sPDCCH cycle may be determined based on system parameters, WTRU-specific parameters, and / or sTTI resource configuration information. The sPDCCH cycle may be determined as an integer multiple of the sTTI length. Different sPDCCH cycles may be used for sTTI resources (e.g., different sTTI resources) that may be configured and / or used. An sDCI may be associated with one or more sPDSCHs.

[0158] An sDCI may be associated with an sPDSCH, and one or more sDCIs may be transmitted or monitored within an sPDCCH region. An sDCI (or DCI) may implicitly or explicitly include or identify an associated sTTI, sPDSCH, or sPDSCH region (e.g., an associated sTTI, sPDSCH, or sPDSCH region). For example, an sPDCCH or sPDCCH region may be associated with one or more sTTIs, sPDSCHs, and / or sPDSCH regions, and scheduling information for an sTTI, sPDSCH, and / or sPDSCH region may be received via an sDCI within the associated sPDCCH or sPDCCH region.

[0159] An RNTI may be used to indicate an sTTI (e.g., an sTTI length or an sTTI time position). For example, the CRC of a DCI or sDCI may be scrambled with an RNTI that may correspond to an sTTI that may be used within the sTTI window. An RNTI associated with a particular sTTI may be used for an sDCI. The RNTI may indicate an sTTI length (or an sTTI time position) for one or more sPDSCHs associated with the sDCI. An RNTI associated with a particular sTTI may be used to indicate an sTTI, for example, for sPDCCH monitoring or an sPDCCH cycle within the sTTI window.

[0160] For example, a set of RNTIs may be used. Each RNTI may be associated with an sTTI, an sTTI length, an sPDCCH cycle, and / or an sPDSCH region. The WTRU may monitor one or more sPDCCHs or sPDCCH regions according to the sTTI length or sPDCCH cycle indicated by the RNTI. The WTRU may monitor one or more sPDCCHs or sPDCCH regions according to the sTTI length or sPDCCH cycle indicated by the RNTI. The WTRU may obtain the sTTI length of the sPDSCH region from the RNTI. The WTRU may use the sTTI length to receive and / or decode the scrambled sPDSCH.

[0161] The RNTI may be used to indicate or identify an sPDSCH or sPDSCH region (e.g., by CRC scrambling with the corresponding RNTI). The RNTI may be used to indicate or identify the time and / or frequency location of one or more sPDCCH regions (e.g., by CRC scrambling with the corresponding RNTI). The WTRU may determine the location of the sPDCCH region and / or sPDSCH region from the RNTI. The WTRU may monitor, receive, attempt to receive, decode, and / or attempt to decode the sPDCCH in the determined location. The WTRU may receive and / or decode a scheduled sPDSCH from the determined location. The terms sPDSCH, sPDSCH region, and sPDSCH in an sTTI may be used interchangeably.

[0162] The location of the sPDCCH candidate (e.g., the number of control channel elements (CCEs) and / or the number of sPDCCH candidates) that may carry the sDCI may determine the associated sTTI location (e.g., the associated sPDSCH region). The WTRU may determine the location of the associated sPDSCH from the location of the sPDCCH. The WTRU may receive and / or decode the scheduled sPDSCH from the determined location. A bit field in the sDCI may be used to indicate the associated sPDSCH region.

[0163] In an sTTI, a signal (e.g., a predefined signal or a known signal) may be transmitted to indicate the presence of an sPDCCH within at least that sTTI. The signal may be transmitted within a position (e.g., a predefined position or a known position) within the sTTI. For example, a PCFICH may be transmitted within a symbol (e.g., the first symbol) of the sTTI to indicate the presence of an sPDCCH within at least that sTTI. When the signal is present or determined to be present by the WTRU, the WTRU may monitor the sPDCCH within at least that sTTI. The signal may indicate at least one of the presence of an sPDCCH within the sTTI, the presence of an sPDCCH within at least one sTTI or sPDCCH region within the sTTI window, the sTTI length, the sPDCCH cycle within the sTTI time window, and the sTTI length for the sPDSCH. The signal may be transmitted within a previous sTTI or sTTI window. The signal may indicate sPDCCH presence and / or one or more of the above parameters for a subsequent or later sTTI or sTTI window.

[0164] The following description may include sPDCCH resource indicators. In one embodiment, DCI within an sPDCCH search space in each sTTI resource may indicate the presence of an sPDCCH resource. In the indicated sPDCCH resource, the WTRU may need to monitor DCIs that may be associated with the sTTI resource allocation. The DCI that indicates the presence of an sPDCCH resource in an sTTI may be referred to as a config-DCI, configuration DCI, or monitoring indicator.

[0165] For example, one or more potential sPDCCH resources may be configured, predefined, used, or determined within a subframe. Whether the WTRU may need to monitor one or more sPDCCH candidates for the sPDSCH and / or sPUSCH within a potential sPDCCH resource may be determined based on the config-DCI. The term "potential sPDCCH resource" may be used interchangeably with the term "sTTI resource" and still be consistent with this disclosure.

[0166] The config-DCI may be monitored within one or more sPDCCH candidates. The one or more sPDCCH candidates that may carry the config-DCI may be located at known positions within each potential sPDCCH resource.

[0167] A single sPDCCH candidate may be used. The time / frequency location and / or (E)CCE aggregation level of the sPDCCH candidate that may carry the config-DCI may be predetermined. For example, the first sPDCCH candidate in the set with the highest (E)CCE aggregation level may be used for the config-DCI. The time / frequency location and / or (E)CCE aggregation level of the sPDCCH candidate that may carry the config-DCI may be configured via higher layer signaling and / or may be dynamically indicated from DCI from a control channel domain, such as a legacy control channel domain (e.g., PDCCH).

[0168] A search space may be defined for config-DCI monitoring. The search space may be common for all WTRUs or for a group of WTRUs. The number of blind code attempts for config-DCI monitoring (e.g., the number of sPDCCH candidates for monitoring config-DCI) may be determined as Nbd. Nbd may be predefined, configured, or determined based on at least one of a number of potential sPDCCH resources within the sTTI time window, a number of symbols used for the sPDCCH resources, a number of (E)CCEs, or a number of PRBs used for the sPDCCH resources. A common search space may be configured or predefined. The common search space may be determined based on at least one of an sTTI length, a number of sTTI resources within the sTTI time window (e.g., subframes), or a number of potential sPDCCH resources within the sTTI time window.

[0169] A specific RNTI may be used for the config-DCI, for example, the config-DCI-RNTI may be used to scramble the CRC of the config-DCI.

[0170] The WTRU may receive, monitor, or attempt to decode one or more sPDCCH candidates that may carry config-DCI within a potential sPDCCH resource. If the WTRU receives config-DCI within a potential sPDCCH resource, the WTRU may start monitoring the sPDCCH candidates for the sPDSCH and / or sPUSCH. If the WTRU does not receive config-DCI within a potential sPDCCH resource, the WTRU may skip monitoring the sPDCCH candidates for the sPDSCH and / or sPUSCH.

[0171] The presence of config-DCI among potential sPDCCH resources may determine the presence of sPDCCH candidates for sPDSCH and / or sPUSCH scheduling. The config-DCI may include one or more of a subset sPDCCH candidate set that may be monitored by the WTRU for the sPDSCH and / or sPUSCH, an aggregation level that may be monitored by the WTRU, or sPDCCH resources for monitoring one or more DCIs associated with the sPDSCH and / or sPUSCH.

[0172] The number of sPDCCH candidates (Mbd) for the sPDSCH and / or sPUSCH may be indicated from the associated config-DCI. For example, the WTRU may monitor Nbd sPDCCH candidates for the config-DCI within the potential sPDCCH resources, and the WTRU may monitor Mbd sPDCCH candidates, where Mbd may be indicated from the config-DCI.

[0173] The WTRU may monitor Mbd sPDCCH candidates for the sPDSCH and / or sPUSCH within the sPDCCH resources. The WTRU may determine Mbd (e.g., the value of Mbd). Mbd may be determined by, from, or based on the number of sPDCCH candidates (Nbd) for the config-DCI. Mbd may be determined by, from, or based on the number of potential sPDCCH resources on which the config-DCI may be received. Mbd may be determined by, from, or based on the number of potential sPDCCH resources within an sTTI time window (e.g., a subframe). Mbd may be determined by, from, or based on the number of sPDCCH resources indicated for monitoring within the potential sPDCCH resources. For example, the WTRU may be indicated to monitor a subset of Nsp potential sPDCCH resources, and Mbd may be determined based on the number of sPDCCHs in that subset. Mbd may be determined by, from, or based on the number of PRBs configured, used, or determined for at least one potential sPDCCH resource. Mbd may be determined by, from, or based on the sTTI length associated with the potential sPDCCH resource.

[0174] Nsp potential sPDCCH resources may be configured, determined, used, or indicated, and the WTRU may receive, monitor, or attempt to decode at least one of the Nsp potential sPDCCH resources for config-DCI. Each potential sPDCCH resource may be configured or determined based on one or more parameters, which may include at least one of a starting symbol, a number of symbols, a number of PRBs, a number of (E)CCEs, or a reference signal type associated with or that may be used for demodulation. The starting symbol of the sPDCCH resource may be determined as a function of the number of sPDCCH resources within an sTTI time window (e.g., a subframe). The number of symbols for the sPDCCH resource may be predetermined, configured, or indicated, for example, by the base station. The potential sPDCCH resources may be configured in a WTRU-specific manner. The terms sTTI window and sTTI time window may be used interchangeably.

[0175] In another embodiment, one or more sPDCCH resources within the sTTI time window may be activated or deactivated for monitoring. The activation and / or deactivation may be configured, received, or indicated via higher layer signaling (e.g., via RRC signaling or via MAC-CE). For example, one or more sPDCCH regions may be used, and each sPDCCH region may include one or more sPDCCH resources. The one or more sPDCCH regions may be located in different frequency resources that may be non-overlapping in frequency within the sTTI time window.

[0176] The WTRU may receive an indication via higher layer signaling (e.g., MAC-CE) in subframe n. This indication may or may not be to activate (or deactivate) one or more sPDCCH regions associated with subframe n. The WTRU may monitor (or skip monitoring) sPDCCH resources in the activated (or deactivated) one or more sPDCCH regions from the indication or higher layer signaling in the subframe. The variable k may be a predefined or configured number.

[0177] A WTRU may be associated with a (e.g., single) sPDCCH region, and one or more sPDCCH resources (or potential sPDCCH resources) may be used. One or more sPDCCH resources within an sPDCCH region may be located in different times (e.g., in different time positions). config-DCI may be monitored by the WTRU in each potential sPDCCH resource if the associated sPDCCH region is activated.

[0178] An sPDCCH (e.g., an sPDCCH region) may include one or more sPDCCH candidates. For example, an sPDCCH region within an sTTI may include N SPDCCH candidates, N SPDCCH may be determined based on at least one of the following parameters: The parameter may be an sPDCCH resource configuration, which may include or identify time and / or frequency resources that may be used. The parameter may be an sTTI resource configuration, which may include or identify time and / or frequency resources that may be used. The parameter may be one or more system parameters. The parameter may be a number of usable resource elements (REs). The number of usable REs may exclude, for example, REs that may be used for at least one of a cell-specific reference signal, a CSI-RS, a DM-RS, and an RS for the sTTI.

[0179] An sPDCCH candidate may carry an sDCI that may be used for at least one of the following: scheduling one or more sPDSCHs, scheduling one or more sPUSCHs, a system information update indication, an sPDCCH order for initiating PRACH transmissions, and activating or deactivating semi-persistent scheduling of an sPUSCH or sPDSCH.

[0180] The sPDCCH candidate may be determined based on one or more reduced TTI control channel elements (sCCEs). One or more sPDCCH candidates may be used, transmitted, and / or monitored within the sPDCCH region. The sPDCCH candidate may be determined based on at least one of the following parameters: the number of sCCEs used, the starting sCCE, the number of starting sCCEs and used sCCEs, the sDCI type carried, and the sCCE type (e.g., localized or distributed).

[0181] An sCCE may be determined or defined as a set of REs in an sPDCCH region. For example, an sCCE may be N consecutive REs in a PRB pair in a downlink OFDM symbol. SCCE,RE RES. One or more of the following parameters may apply: N SCCE,RE may be 12. The number of sCCEs in the sPDCCH region may be determined based on the number of PRBs and the number of OFDM symbols used for the sPDCCH region. The reference signal type, the number of antenna poles, and / or the number of antenna poles used for the sCCE may be determined based on (or as a function of) at least one of the sTTI resource type, system parameters, WTRU-specific parameters, the number of associated PRBs, and the transmission mode (e.g., CRS-based transmission mode or DM-RS-based transmission mode) used for the associated sPDSCH transmission. The sCCEs may be determined, defined, and / or configured with one or more shortened TTI resource element groups (sREGs).

[0182] In another embodiment, a subset of nPDCCH resources may be used as sPDCCH resources. For example, Ncce (E)CCEs may be located within the nPDCCH region, and a subset of the (E)CCEs may be used for sPDCCH transmission. The subset of (E)CCEs may be determined based on one or more of the following parameters: A predefined set of (E)CCEs may be used. For example, the first Ns (E)CCEs (excluding (E)CCEs used for the common search space) may be used as the set of (E)CCEs for sPDCCH transmission.

[0183] The first Ncom (E)CCEs may be used for the nPDCCH common search space, and Ncom+1 through Ncom+Ns (E)CCEs may be used for sPDCCH transmissions. In one example, Ncom may be 16. The WTRU may attempt to decode, monitor, or receive nPDCCH candidates that may not include one or more (E)CCEs used for the sPDCCH. For example, if an nPDCCH candidate in a WTRU-specific search space includes one or more (E)CCEs for sPDCCH transmission, the WTRU may skip monitoring the nPDCCH candidate.

[0184] The subset of (E)CCEs may be configured via higher layer signaling. The starting (E)CCE number and / or the number of (E)CCEs may be configured, for example, via higher layer signaling. The subset of (E)CCEs may be determined as a function of Ncce. The subset of (E)CCEs may be dynamically indicated from DCI within a common search space. The subset of (E)CCEs may be replaced by (E)REG or (E)CCE / (E)REG.

[0185] An sPDCCH search space may be provided and / or used. The sPDCCH search space may include one or more sPDCCH candidates. The sPDCCH search space may be cell-specific, WTRU-specific, and / or physical channel-specific. The sPDCCH search space may include one or more sPDCCH candidates that may be associated with one or more sPDCCH search space types (e.g., cell-specific, WTRU-specific, and / or physical channel-specific).

[0186] A WTRU may attempt to decode, monitor, receive, or attempt to receive sPDCCH candidates within an sPDCCH search space that may be associated with the WTRU. The sPDCCH candidates within an sPDCCH search space may be blind decoded for an sDCI scrambled with an RNTI that may be associated with the WTRU. The number of blind decoding attempts within an sPDCCH search space may be the same as the number of sPDCCH candidates in the sPDCCH search space.

[0187] In one embodiment, the sPDCCH search space may be defined, configured, or determined per sTTI time window. For example, the sTTI time window may include one or more sPDCCH regions, and the WTRU may monitor or attempt to decode one or more sPDCCH regions within the sTTI time window.

[0188] In one example, the total number of blind decoding attempts (e.g., the total number of PDCCH candidates) within the sTTI time window may be divided into (or across or among) the number of sPDCCH regions. If the number of sPDCCH regions is increased, the number of blind decoding attempts (e.g., the number of PDCCH candidates) within the sPDCCH region may be reduced. The number of sPDCCH candidates within the sPDCCH region may be determined based on the number of sPDCCH regions configured or determined within the sTTI time window. The terms sPDCCH region and / or sPDCCH search space may be used interchangeably.

[0189] Within an sTTI time window, at least one cell-specific sPDCCH region and at least one WTRU-specific sPDCCH region may be used, configured, and / or determined. The cell-specific sPDCCH region and the WTRU-specific sPDCCH region may be located within non-overlapping time / frequency resources. The cell-specific sPDCCH region may be located within the first sPDCCH region within the sTTI time window. The WTRU-specific sPDCCH region may be located within one or more sPDCCH regions that may not be used as cell-specific sPDCCH regions. The WTRU-specific sPDCCH region may be a subset of the cell-specific sPDCCH region. For example, a cell-specific sPDCCH region may be configured for each sTTI, and a WTRU-specific sPDCCH region may be determined or configured within a subset of sTTIs within the sTTI time window.

[0190] The WTRU may determine a number of sPDCCH regions within the sTTI time window. The number of sPDCCH regions within the sTTI time window may be determined in a WTRU-specific manner. The number of sPDCCH candidates within the sPDCCH region may be determined based on the TTI length of the sPDCCH region and / or the sTTI length of the associated sPDSCH.

[0191] The WTRU may determine a number of sPDCCH candidates within the sPDCCH region. The WTRU may monitor one or more sPDCCH candidates, e.g., a determined number of sPDCCH candidates, within the sPDCCH region. The number of sPDCCH candidates within the sPDCCH region may be determined based on the number of sPDSCHs (or sTTIs) associated with the sPDCCH region. For example, if one sTTI or one sPDSCH is associated with the sPDCCH region, a first number of sPDCCH candidates may be monitored within the sPDCCH region. If multiple sTTIs or multiple sPDSCHs are associated with the sPDCCH region, a second number of sPDCCH candidates may be monitored within the sPDCCH region. The second number of sPDCCH candidates may be greater than the first number of sPDCCH candidates. If m1 sPDCCH candidates are monitored within an sPDCCH region when the sPDCCH region is associated with an sPDSCH region (or one sTTI), then m2 sPDCCH candidates may be monitored within the sPDCCH region when the sPDCCH region is associated with multiple sPDSCH regions (e.g., sTTIs). The value m2 may be an integer multiple of m1 (e.g., m2 = m1 × K), where K may be the number of sPDSCH regions associated with the sPDCCH region.

[0192] In another embodiment, an sPDCCH search space may be defined, configured, or determined per sTTI. A predefined or configured number of sPDCCH candidates may be monitored within each sPDCCH region. One or more of the following parameters may apply:

[0193] The WTRU may skip monitoring sPDCCH candidates within an sTTI (or sPDCCH region) if one or more of the following conditions are met: An sPDSCH may be scheduled within an sTTI or within an sTTI window, for example, by scheduling within a previous sPDCCH (e.g., an sPDCCH within a previous sTTI). An sTTI may be associated with a WTRU (or a WTRU-ID). This association may be predetermined, configured, or dynamically indicated. An sTTI may not be used for one or more physical channels, such as the sPDCCH and / or sPDSCH. In an sTTI, the resources available for the sTTI may be below a threshold, which may be defined (e.g., predefined) or configured. The WTRU may monitor the sPDCCH within a subset of sTTIs that may be used for the sPDCCH search space.

[0194] In one example, the nPDCCH search space and one or more potential sPDCCH search spaces may be located within an sTTI time window (e.g., a subframe). The number of nPDCCH candidates that may be monitored by the WTRU may be determined, for example, by the WTRU based on the number of sPDCCH search spaces configured or present within the sTTI time window.

[0195] For example, one or more potential sPDCCH search spaces may or may not be present within the sTTI time window. The presence of one or more sPDCCH search spaces may be indicated from indicators described herein (e.g., sTTI resource indicator, config-DCI, etc.). The number of nPDCCH candidates may be determined, for example, by the WTRU, based on the number of sPDCCH search spaces within the sTTI time window.

[0196] Note that the term "sPDCCH search space" may be used interchangeably with the terms "sTTI resource," "sPDCCH resource," and "sTTI." If the sPDCCH search space does not lie within the sTTI time window, the number of nPDCCH candidates may be the same as the number of legacy PDCCH candidates. If a greater number of sPDCCH search spaces are located within or used within the sTTI time window, a smaller number of nPDCCH candidates may be monitored by the WTRU. If the number of sPDCCH search spaces is greater than a predefined or configurable threshold, the WTRU may not monitor nPDCCH candidates within a WTRU-specific search space.

[0197] In another embodiment, the nPDCCH search space and one or more potential sPDCCH search spaces may be located within an sTTI time window (e.g., a subframe). The monitoring of the nPDCCH search space may be determined, for example, by the WTRU, based on the nPDCCH type and the presence of one or more sPDCCH search spaces.

[0198] If at least one sPDCCH search space exists, the search space of a first nPDCCH type may not be monitored, for example, by the WTRU, while the search space of a second nPDCCH type may be monitored, for example, by the WTRU. For example, the first nPDCCH type may be an EPDCCH and the second nPDCCH type may be a PDCCH. If an sPDCCH search space exists, nPDCCH candidates of the first nPDCCH type may be switched to nPDCCH candidates of the first nPDCCH type.

[0199] The WTRU may be configured with a first nPDCCH type for a WTRU-specific search space. The WTRU-specific search space may be based on the first nPDCCH type (e.g., EPDCCH) if the WTRU does not need to monitor an sPDCCH search space in a subframe. The WTRU-specific search space may be based on a second nPDCCH type (e.g., PDCCH) if the WTRU needs to monitor one or more sPDCCH search spaces in a subframe.

[0200] The following description may include sPDCCH and nPDCCH joint operation. In one embodiment, a joint sPDCCH and normal PDCCH (nPDCCH) search space may be used. The normal PDCCH (e.g., legacy PDCCH, nPDCCH) search space and the sPDCCH search space may be configured (e.g., jointly configured) within an sTTI time window. For example, the normal PDCCH (nPDCCH) search space (or nPDCCH region) may be located within the sTTI time window. A DCI (e.g., a specific DCI), referred to herein as nTTI, may be transmitted within at least one nPDCCH search space.

[0201] The nPDCCH may include one or more nPDCCH candidates, which may carry one or more nDCIs that may be used for nTTI operation. The nPDCCH may be at least one of a PDCCH, an extended PDCCH (EPDCCH), an MTC PDCCH (M-PDCCH), and a narrowband PDCCH (NB-PDCCH). The nDCI may include information regarding the sPDCCH search space. Several sPDCCH candidates may be included in the nDCI. A subset of the sPDCCH region within the sTTI time window may be indicated in the nDCI, and the WTRU may monitor the sPDCCH candidates within that subset of the sPDCCH region. Several sCCEs within the sPDCCH region may be indicated in the nDCI. An sTTI resource configuration, including at least one of a time resource configuration, a frequency resource configuration, a spatial resource configuration, and an sTTI length, may be indicated in the nDCI. For example, sDCI that cannot be transmitted in the associated sPDCCH region due to collision with other signals or limited resources may be indicated in the nDCI.

[0202] In one embodiment, the nDCI may be used to configure a mode of operation. For example, two modes of operation (e.g., normal TTI mode and reduced TTI mode) may be used, and the nDCI may configure, indicate, or (de)activate the associated mode of operation. The WTRU may monitor the nDCI in an nPDCCH region. The WTRU may determine the mode of operation based on the information in the nDCI. The WTRU may monitor PDCCH candidates in one or more PDCCH regions based on the determined mode of operation. If the WTRU determines a first mode of operation (e.g., normal TTI), the WTRU may monitor nPDCCH candidates in one or more nPDCCH regions. If the WTRU determines a second mode of operation (e.g., reduced TTI), the WTRU may monitor sPDCCH candidates in one or more sPDCCH regions.

[0203] The nDCI may be transmitted within at least one and every sTTI time window. The sTTI time window may be a time window for a certain mode of operation. The nDCI may be transmitted within a subset of subframes and / or SFNs. The nDCI may be transmitted within a common search space within an nPDCCH region that may be monitored (e.g., jointly) by WTRUs configured for sTTI operation.

[0204] In another embodiment, the nDCI may be used as a fallback DCI between at least two operating modes. For example, when a WTRU is configured with an operating mode or transmission mode (e.g., an sTTI operating mode or an sTTI transmission mode), the WTRU may monitor the nPDCCH region to receive the nDCI.

[0205] In one embodiment, a WTRU may be dynamically indicated to monitor, attempt to decode, or receive one or more sPDCCH search spaces within an sTTI time window (e.g., subframe), and the WTRU may determine a set (or subset) of nPDCCH candidates within the nPDCCH search space based on the indication.

[0206] If a WTRU receives an indication of the presence of one or more sPDCCH search spaces within an sTTI time window, the WTRU may skip monitoring the nPDCCH search space within that sTTI time window. If a WTRU receives an indication that there is no sPDCCH search space within an sTTI time window, the WTRU may monitor the nPDCCH search space.

[0207] If a WTRU receives an indication of the presence of one or more sPDCCH search spaces, the WTRU may monitor only the nPDCCH common search space and may skip monitoring the nPDCCH UE-specific search spaces. The indication of the presence of one or more sPDCCH search spaces may be received in a DCI that may be monitored, received, or signaled in the nPDCCH common search space, or may be received in one or more CCEs in a given nPDCCH region.

[0208] If a WTRU receives an indication of the presence of one or more sPDCCH search spaces within an sTTI time window, the WTRU may monitor, attempt to decode, or receive a subset of nPDCCH candidates within the associated nPDCCH search space within that sTTI time window. Also, if a WTRU receives an indication that one or more sPDCCH search spaces are absent within an sTTI time window, the WTRU may monitor, attempt to decode, or receive the full set of nPDCCH candidates within the associated nPDCCH search space within the sTTI time window.

[0209] The complete set of nPDCCH candidates may be the same as the nPDCCH candidates that the WTRU may need to monitor in an nPDCCH WTRU-specific search if the WTRU is not configured with sPDCCH monitoring or sTTI operation mode. The subset of nPDCCH candidates may be determined based on at least one of the following parameters: the presence of one or more sPDCCH search spaces; the sPDCCH search space may be defined, determined, or configured as an sPDCCH search space associated with an sTTI; the number of sPDCCH search spaces within the sTTI time window; the number of sPDCCH candidates for the sPDCCH search space; and / or the number of total sPDCCH candidates for the presented or indicated sPDCCH search space(s).

[0210] The presence of one or more sPDCCH search spaces within the sTTI time window may be indicated within the nPDCCH region. The number of sPDCCH search spaces may be explicitly indicated within a DCI that may be monitored within the nPDCCH region. The sTTI length associated with one or more sPDCCH search spaces may be indicated, and the number of sPDCCH search spaces may be determined as a function of the indicated sTTI length.

[0211] The subset of nPDCCH candidates may be determined based on the CCE aggregation level, for example, if the presence of one or more sPDCCH search spaces is indicated, a subset of the CCE aggregation levels may be monitored.

[0212] In another embodiment, a set (or a subset) of nDCI types that may be monitored within an nPDCCH search space may be determined based on the presence of one or more sPDCCH search spaces and / or sDCI types within an sTTI time window. One or more sPDCCH search spaces and / or sDCI types within an sTTI time window may be monitored within the sPDCCH search space.

[0213] A WTRU may be indicated, configured, or determined to monitor one or more sDCI types within one or more sPDCCH search spaces. For example, a first sDCI type may be associated with an sPDSCH transmission and a second sDCI type may be associated with an sPUSCH transmission. If a WTRU is indicated, configured, or determined to monitor a first sDCI type within one or more sPDCCH search spaces within an sTTI time window, the WTRU may monitor a set (or a subset) of nPDCCH candidates for the nDCI type associated with the nPUSCH transmission and may skip monitoring nPDCCH candidates for the nDCI type associated with the nPDSCH transmission.

[0214] The WTRU may monitor nDCI or sDCI for the same transmission direction (downlink or uplink). The WTRU may be scheduled (or assumed to be scheduled) with an sPDSCH or nPDSCH within the sTTI time window. The WTRU may be scheduled (or assumed to be scheduled) with an sPUSCH or nPUSCH within the sTTI time window.

[0215] If a WTRU is indicated, configured, or determined to monitor an sDCI associated with an sPUSCH transmission within an sTTI time window (e.g., subframe n), the WTRU may skip monitoring an nDCI associated with an nPUSCH transmission within the same sTTI time window (e.g., subframe n). The sPUSCH and nPUSCH transmissions within the same sTTI time window may include full or partial overlap of the sPUSCH and nPUSCH transmissions.

[0216] In another example, the WTRU may receive an indication of which subset of sPDCCH candidates to monitor. For example, one or more subsets of sPDCCH candidates may be configured, defined, predefined, determined, or predetermined, and one of the subsets may be indicated in the DCI.

[0217] DL reference signals for sPDSCH and sPDCCH channels may be required. sPDSCH and / or sPDCCH transmissions may be associated with one or more reference signal types (e.g., CRS, DM-RS), antenna ports, and / or precoding granularity. One or more reference signal types may be used. The reference signal type may be determined based on at least one of the following parameters: The parameter may be the scrambling sequence used. For example, a parameter used for scrambling sequence initialization (e.g., physical cell ID, WTRU-ID, virtual cell ID) may be used. The parameter may be the reference signal position within the time and frequency grid. The parameter may be the precoding granularity of the reference signal. Within a certain precoding granularity, the WTRU may use the reference signal for channel estimation for the same antenna port. The parameter may be a WTRU-specific or cell-specific configuration. The parameter may be the reference signal power. The parameter may be the reference signal overhead within a certain time / frequency resource. For example, RS Type 0 may have zero reference signal overhead (e.g., no reference signal) for sPDSCH and / or sPDCCH transmissions, RS Type 1 may have 10% reference signal overhead, and RS Type 2 may have 20% reference signal overhead.

[0218] The reference signal type may be determined based on a transmission mode configured for the sPDSCH. The reference signal type may be indicated in downlink control information associated with the sPDCCH or the sPDSCH resource. The downlink control information for the sPDSCH resource may be sDCI, which may be carried in an sPDCCH region. The downlink control information for the sPDCCH resource may be nDCI, which may be carried in an nPDCCH region.

[0219] In one embodiment, the reference signal type associated with an sPDSCH and / or sPDCCH transmission may be determined based on at least one of the following parameters: The parameter may be the transmission mode or transmission scheme used; The parameter may be the time position of the sTTI or the number of sTTIs within the sTTI time window; The parameter may be the modulation and coding scheme (MCS) used for the associated channel; The parameter may be the number of sTTIs bundled for the sPDSCH transmission. For example, if a single sPDSCH is scheduled within the sTTI time window, RS type 1 may be used for the sPDSCH transmission, while when multiple sPDSCHs are scheduled within the sTTI time window, RS type 2 may be used for the remaining portion of the first sPDSCH and RS type 0 may be used for the remaining portions of the sPDSCHs.

[0220] In another embodiment, the presence of a reference signal within an sTTI for an sPDSCH and / or an sPDCCH may be determined based on the position of the sTTI or the number of sTTIs within the sTTI time window. sTTI is located within the sTTI time window, and each sTTI within the sTTI time window is from 0 to N sTTI-1 , the reference signal may be present within (e.g., only within) a subset of the sTTI numbers (even-numbered sTTIs or odd-numbered sTTIs).

[0221] A method for sPDCCH resource allocation is needed. In one embodiment, sCCEs may be defined, configured, and / or used within an sTTI resource. The sCCEs may be used for sPDCCH and / or sPDSCH transmissions. For example, a subset of sCCEs may be used for sPDCCH transmissions, and the remaining portion of the sCCEs may be used for sPDSCH transmissions.

[0222] An sTTI resource may be defined, configured, or determined based on a set of sCCEs. The number of sCCEs within the sTTI resource may be determined based on the time / frequency resources used for the sTTI. A first subset of sCCEs within the sTTI resource may be defined or determined as an sPDCCH region, and a second subset of sCCEs within the sTTI resource may be defined or determined as an sPDSCH region. A WTRU may receive an sDCI within the sPDCCH region, and the WTRU may receive an associated sPDSCH within the sPDSCH region. The first subset of sCCEs and the second subset of sCCEs may be mutually exclusive. The first subset of sCCEs and the second subset of sCCEs may overlap fully or partially.

[0223] The sPDCCH region may be determined based on the sPDCCH candidates used for the sDCI transmission. The number of sCCEs for the sPDCCH region may be determined based on the number of sCCEs used for the sPDCCH transmission, and the remaining portion of the sCCEs may be considered as the sPDSCH region. The number of sCCEs used for the sPDCCH transmission may be indicated from the associated sDCI for the sPDSCH transmission.

[0224] The sPDCCH region may be determined based on the number of sCCEs used for transmission of the sDCI. The sPDSCH region (or sPDSCH resource allocation) may be dynamically indicated from the associated sDCI. For example, a starting sCCE number and an ending sCCE number may be indicated. If one or more sCCEs are not used for sPDCCH transmission, the sTTI resources configured for the sPDCCH may be used for sPDSCH transmission.

[0225] In another embodiment, one or more sPDCCH candidates may be used for sPDSCH transmission. For example, an sTTI resource may be defined as an sPDCCH search space, and one or more sPDCCH candidates within the sPDCCH search space may be used for sPDSCH transmission. The number of sPDCCH candidates may be indicated for the sPDSCH transmission. The starting and ending numbers of sPDCCH candidates may be indicated from the associated sDCI for the sPDSCH transmission.

[0226] System information (SI) updates in sTTI operation may be provided. The WTRU may monitor the nPDCCH common search space and receive a DCI with a P-RNTI for an SI update. The DCI with the P-RNTI may include scheduling information for a PDSCH, which may include a paging message. The paging message may include at least one of an SI update, an Earthquake and Tsunami Warning System (ETWS), a Commercial Mobile Alert Service (CMAS), or an Extended Access Barring (EAB) parameter. Hereinafter, the SI update, ETWS, CMAS, and / or EAB may all be referred to as a "direct indication." The direct indication may also include a valueTag and an SI update per SI message.

[0227] When monitoring the nPDCCH search space in a subframe, the WTRU may attempt to receive a direct indication from a paging message. The WTRU may attempt to receive a direct indication from a DCI in the sPDCCH search space, if one or more sPDCCH search spaces exist. sPDCCH candidates for DCIs that may carry a direct indication may be monitored in a known location (e.g., an sPDCCH common search space). One or more sPDCCH candidates may be monitored by the WTRU for DCIs that may carry a direct indication. DCIs that may carry a direct indication may be scrambled with a particular RNTI (e.g., a direct RNTI).

[0228] The WTRU may attempt to receive a direct indication from a DCI in an nPDCCH search space, if one or more sPDCCH search spaces exist. nPDCCH candidates for DCIs that may carry a direct indication may be monitored in a known location (e.g., an nPDCCH common search space). One or more nPDCCH candidates may be monitored by the WTRU for DCIs that may carry a direct indication. DCIs that may carry a direct indication may be scrambled with a particular RNTI (e.g., a direct RNTI).

[0229] In another embodiment, the WTRU may skip monitoring one or more sPDCCH candidates in a subframe if the UE may need to monitor DCI with a P-RNTI. For example, if the UE may need to monitor paging messages in the nPDCCH common search space, the UE may skip monitoring one or more sPDCCH candidates in a subframe.

[0230] RE muting of sTTI resources may be implemented. In one example, one or more REs (e.g., sPDCCH, sPDSCH) within an sTTI resource may be muted if those REs are used, configured, and / or occupied for one or more reference signals. The reference signals may include, but are not limited to, at least one of periodic CSI-RS, aperiodic CSI-RS, demodulation RS (DM-RS), cell-specific RS (CRS), and positioning RS (PRS). One or more of the following parameters may apply:

[0231] The presence of a reference signal within an sTTI resource may be determined based on higher layer configuration, and thus the presence of a reference signal (e.g., periodic CSI-RS, CRS, or PRS) may be known to the WTRU for the sTTI time window.

[0232] The presence of reference signals and / or reference signal configurations within sTTI resources may be dynamically indicated in a DCI. The DCI may be received, monitored, decoded, and / or transmitted within one or more of the following resources and according to one or more of the following parameters: The DCI may include configuration information of the indicated reference signals. For example, one or more CSI-RS reuse patterns may be indicated in the DCI, and REs to be used for the indicated one or more CSI-RS reuse patterns may be muted.

[0233] The DCI may be monitored within the nPDCCH region. An indication may be transmitted within the DCI, which may be used to indicate the presence of one or more sTTI resources or one or more sPDCCH search spaces. The indication may be transmitted within an sDCI associated with one or more sPDSCH transmissions if a reference signal is presented within the associated one or more sPDSCH transmissions. The reference signal configuration may include at least one of one or more CSI-RS reuse patterns, a set of frequency resources on which a CSI-RS transmit power reference signal of the indicated one or more CSI-RS reuse patterns is presented, and a number of consecutive subframes on which the reference signal is presented.

[0234] RE muting may be referred to as RE puncturing or RE rate matching. The use of RE puncturing or RE rate matching may be dynamically indicated for a certain reference signal. For example, RE rate matching may be used for periodic CSI-RS, while RE muting (RE puncturing or RE rate matching) may be indicated in a DCI for aperiodic CSI-RS. The DCI for RE muting type indication may be monitored within a common search space (e.g., nPDCCH common search space).

[0235] In some cases, the number of available REs in an sTTI resource (e.g., an sPDCCH resource and / or an sPDSCH resource) may be used by the WTRU to determine whether to monitor the sPDCCH search space. For example, the WTRU may calculate, determine, estimate, or count the number of available REs in the sTTI resource. If the number of available REs in the sTTI resource is lower than a threshold, the WTRU may skip monitoring the corresponding sPDCCH.

[0236] One or more of the reference signals (e.g., periodic CSI-RS, aperiodic CSI-RS, IMR, CRS, DM-RS, PRS, and discovery RS), the physical broadcast channel (PBCH), the synchronization signal (e.g., PSS or SSS), and the nPDCCH may be considered as unavailable REs.

[0237] The threshold may be determined as a function of the sTTI length. For example, if a first sTTI length (e.g., 2 symbols) is used, a first threshold number (e.g., N1) may be used, and if a second sTTI length (e.g., 7 symbols) is used, a second threshold number (e.g., N2) may be used. One or more threshold numbers may be predefined, configured, or dynamically indicated. The associated threshold number may be dynamically indicated in a DCI used to indicate presence in the sTTI resource within the sTTI time window. The DCI may be monitored within an nPDCCH region (e.g., an nPDCCH common search space or a known location within the nPDCCH region).

[0238] The threshold number may be determined as a function of the number of frequency resources used for the sTTI resource. Periodic CSI-RS, which may be configured via higher layer signaling, may be considered as unavailable REs, while aperiodic CSI-RS, which may be indicated in the DCI, may be considered as available REs.

[0239] In another embodiment, the number of sTTI resources for downlink transmission (e.g., sPDSCH and / or sPDCCH) may be determined based on the number of available REs in the sTTI resource. For example, if the number of available REs for an sTTI resource is lower than a threshold, that sTTI resource may be used (or bundled) with one or more consecutive sTTI resources within the sTTI time window.

[0240] If the number of available REs for an sTTI resource (e.g., resource #n) within the sTTI time window is lower than a threshold, the number of available REs may be counted by combining the next sTTI resource (e.g., sTTI resource #n+l). If the number of available REs for the combined (or bundled) sTTI resources is higher than a threshold number, the WTRU may monitor the sPDCCH search space within those combined (or bundled) sTTI resources. The timing of HARQ-ACK and sPUSCH transmissions may be based on the latest sTTI resource within the bundled sTTI resources. If K sTTI resources are combined or bundled, the effective sTTI length may be increased by a factor of K.

[0241] The number of sPDCCH candidates in each sPDCCH region for blind decoding may be determined based on the number of sTTI resources in a subframe. If the number of sTTI resources in a subframe is greater, fewer sPDCCH candidates may be monitored. A common search space definition for the legacy PDCCH and sPDCCH may be used for dynamic configuration between normal TTI and shortened TTI. Fallback DCI may be monitored within the common search space.

[0242] A set of sCCEs may be used within the sTTI resource, and the sPDCCH and sPDSCH may be transmitted within mutually exclusive subsets of the sCCEs. A first subset of the sCCEs may be determined as the sPDCCH carrying DCI for sPDSCH scheduling within the sTTI resource. The remaining sCCEs may be used to transmit the sPDSCH.

[0243] Although features and elements are described above in particular combinations, those skilled in the art will understand that each feature or element can 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 via wired or wireless connections) and computer-readable storage media. Examples of computer-readable storage media include, but are not limited to, read-only memory (ROM), random-access memory (RAM), registers, cache memory, semiconductor memory devices, magnetic media such as internal hard disks and removable disks, magneto-optical media, 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, base station, RNC, or any host computer.

Claims

1. 1. A wireless transmit / receive unit (WTRU), comprising: a processor; A transceiver; Equipped with the processor and the transceiver are configured to receive configuration information configuring a set of normal physical downlink control channel (nPDCCH) candidates; The processor and the transceiver are configured to receive a first transmission including first downlink control information (DCI), the first DCI including a first monitoring indicator having a first value; the processor and the transceiver are configured to skip monitoring the set of nPDCCH candidates within a first time window based on the first monitoring indicator; the processor and the transceiver are configured to receive a second transmission including a second DCI, the second DCI including a second monitoring indicator having a second value; the processor and the transceiver are configured to monitor the set of nPDCCH candidates within a second time window based on the second monitoring indicator; the processor and the transceiver are configured to receive a third transmission in the set of monitored nPDCCH candidates, the third transmission including a third DCI indicating at least one of a downlink grant or an uplink grant. WTRU.

2. 2. The WTRU of claim 1, wherein the first monitoring indicator having the first value indicates the presence of a set of shortened physical downlink control channel (sPDCCH) candidates within the first time window.

3. The WTRU of claim 1 , wherein the second monitoring indicator having the second value indicates an absence of a set of shortened physical downlink control channel (sPDCCH) candidates within the second time window.

4. The WTRU of claim 1 , wherein the configuration information includes an indication of a time resource on which the first monitoring indicator and the second monitoring indicator are located.

5. The WTRU of claim 1 , wherein the transceiver is configured to send or receive transmissions based on at least one of the downlink grant or the uplink grant.

6. The WTRU of claim 3 , wherein the first time window is a reduced transmission time interval (sTTI) time window.

7. The WTRU of claim 1 , wherein the third DCI includes scheduling information for sending or receiving abbreviated transmissions.

8. 2. The WTRU of claim 1, wherein the processor and the transceiver are configured to skip monitoring the set of nPDCCH candidates by not monitoring the set of nPDCCH candidates during a first time window.

9. 2. The WTRU of claim 1, wherein the first time window and the second time window are defined by one or more symbols, one or more subframes, one or more frames, one or more time slots, or one or more time samples.

10. The WTRU of claim 1 , wherein the configuration information is conveyed via radio resource control (RRC) signaling.

11. 1. A method performed by a wireless transmit / receive unit (WTRU), comprising: receiving configuration information configuring a set of normal physical downlink control channel (nPDCCH) candidates; receiving a first transmission including first downlink control information (DCI), the first DCI including a first monitoring indicator having a first value; skipping monitoring the set of nPDCCH candidates within a first time window based on the first monitoring indicator; receiving a second transmission including a second DCI, the second DCI including a second monitoring indicator having a second value; monitoring the set of nPDCCH candidates within a second time window based on the second monitoring indicator; receiving a third transmission in the set of monitored nPDCCH candidates, the third transmission including a third DCI indicating at least one of a downlink grant or an uplink grant; A method comprising:

12. 12. The method of claim 11, wherein the first monitoring indicator having the first value indicates the presence of a set of shortened physical downlink control channel (sPDCCH) candidates within the first time window.

13. 12. The method of claim 11, wherein the second monitoring indicator having the second value indicates the absence of a set of shortened physical downlink control channel (sPDCCH) candidates within the second time window.

14. The method of claim 11 , wherein the configuration information includes an indication of a time resource on which the first monitoring indicator and the second monitoring indicator are located.

15. The method of claim 11 , comprising sending or receiving a transmission based on at least one of the downlink grant or the uplink grant.

16. The method of claim 13 , wherein the first time window is a reduced transmission time interval (sTTI) time window.

17. The method of claim 11 , wherein the third DCI includes schedule information for sending or receiving abbreviated transmissions.

18. 12. The method of claim 11, comprising skipping monitoring the set of nPDCCH candidates by not monitoring the set of nPDCCH candidates during a first time window.

19. 12. The method of claim 11 , wherein the first time window and the second time window are defined by one or more symbols, one or more subframes, one or more frames, one or more time slots, or one or more time samples.

20. The method of claim 11 , wherein the configuration information is conveyed via radio resource control (RRC) signaling.

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