Patent Description:
The present disclosure relates generally to wireless communication systems, and more particularly to control channel transmission and reception in an Orthogonal Frequency Division Multiplexing (OFDM) communication system.

In current 3GPP LTE (Third Generation Partnership Project Long Term Evolution), time-frequency resources are divided into subframes where each <NUM> subframe comprises two <NUM> slots and each slot (with normal CP duration) comprises <NUM> SC-FDMA symbols in time domain in uplink (UL) and <NUM> OFDM symbols in time domain in downlink (DL). In frequency domain, resources within a slot are divided into physical resource blocks (PRBs), where each resource block spans <NUM> contiguous subcarriers.

In current LTE systems, resources are typically assigned using a <NUM> minimum transmission time interval (TTI) when data is available, in a process referred to as dynamic scheduling. Within each scheduled TTI in UL, the UE transmits data over a physical uplink shared channel (PUSCH) in PRB-pairs indicated by an uplink grant to the UE that schedules the data transmission. In DL, the evolved Node B (eNB) transmits data over a physical downlink shared channel (PDSCH) in PRB-pairs indicated by a DL grant/assignment. The UL grant and/or DL assignment information is provided to the UE in a control channel, referred to as a (enhanced) physical downlink control channel PDCCH or EPDCCH. The PDCCH/EPDCCH channel carries the control information about the data being transmitted on the current subframe and the information about the resources that the UE needs to use for the uplink data. In<NPL>, there is described separation of DCI into fast and slow DCI to minimize signaling overhead carried in the shorter TTI interval. The fast DCI is always located in the first symbol of the shorter TTI interval.

The description of the illustrative embodiments is to be read in conjunction with the accompanying drawings, wherein:.

The illustrative embodiments of the present disclosure provide a method and user equipment (UE) that implements control channel monitoring to enable reduced latency operation. The dependent claims provide advantageous embodiments. In the following detailed description of exemplary embodiments of the disclosure, specific exemplary embodiments in which the various aspects of the disclosure may be practiced are described in sufficient detail to enable those skilled in the art to practice the invention, and it is to be understood that other embodiments may be utilized and that logical, architectural, programmatic, mechanical, electrical and other changes may be made without departing from the scope of the present disclosure. The following detailed description is, therefore, not to be taken in a limiting sense, and the scope of the present disclosure is defined by the appended claims. Within the descriptions of the different views of the figures, similar elements are provided similar names and reference numerals as those of the previous figure(s). The specific numerals assigned to the elements are provided solely to aid in the description and are not meant to imply any limitations (structural or functional or otherwise) on the described embodiment. It is understood that the use of specific component, device and/or parameter names, such as those of the executing utility, logic, and/or firmware described herein, are for example only and not meant to imply any limitations on the described embodiments. The embodiments may thus be described with different nomenclature and/or terminology utilized to describe the components, devices, parameters, methods and/or functions herein, without limitation. References to any specific protocol or proprietary name in describing one or more elements, features or concepts of the embodiments are provided solely as examples of one implementation, and such references do not limit the extension of the claimed embodiments to embodiments in which different element, feature, protocol, or concept names are utilized. Thus, each term utilized herein is to be given its broadest interpretation given the context in which that terms is utilized. As further described below, implementation of the functional features of the disclosure described herein is provided within processing devices and/or structures and can involve use of a combination of hardware, firmware, as well as several software-level constructs (e.g., program code and/or program instructions and/or pseudo-code) that execute to provide a specific utility for the device or a specific functional logic. The presented figures illustrate both hardware components and software and/or logic components. Those of ordinary skill in the art will appreciate that the hardware components and basic configurations depicted in the figures may vary. The illustrative components are not intended to be exhaustive, but rather are representative to highlight essential components that are utilized to implement aspects of the described embodiments. For example, other devices/components may be used in addition to or in place of the hardware and/or firmware depicted. The depicted example is not meant to imply architectural or other limitations with respect to the presently described embodiments and/or the general invention.

Embodiments incorporating teachings of the present disclosure are shown and described with respect to the figures presented herein.

<FIG> illustrates an example user equipment (UE) <NUM> such as a wireless communication device (WCD), operating in a communication system <NUM> such as a Wireless Wide Area Network (WWAN), within which the functional aspects of the described embodiments may be implemented. UE <NUM> represents a device that is adapted to transmit and receive electromagnetic signals over an air interface via uplink and/or downlink channels between the UE <NUM> and communication network equipment (e.g., base-station <NUM>) utilizing at least one communication standard, such as Global System for Mobile Communications (GSM), Code Division Multiple Access (CDMA), Orthogonal Frequency Division Multiple Access (OFDMA), Universal Mobile Telecommunications Service (UMTS), Long Term Evolution (LTE), Wireless Local Area Networks (WLAN) (e.g. Wi-Fi) and other wireless communication systems. In one or more embodiments, the UE can be a mobile cellular device/phone or smartphone, or laptop, netbook or tablet computing device, or other types of communications devices.

UE <NUM> comprises processor <NUM> and interface circuitry <NUM>, which are connected to memory component <NUM> via signal bus <NUM>. UE <NUM> also comprises sensor(s) <NUM>. In one embodiment, sensor(s) <NUM> is used to measure temperature(s) of RF circuit components, including tuning circuit components. In addition, UE <NUM> comprises input/output (I/O) devices <NUM>. Also included within UE <NUM> are radio frequency (RF) tuner (tuning circuit) <NUM>, transceiver integrated circuit (IC) <NUM> which is communicatively coupled to tuning circuit <NUM>, and modem <NUM> which is communicatively coupled to transceiver IC <NUM>. In one embodiment, modem <NUM> includes digital signal processor (DSP) <NUM>. As illustrated within WCD <NUM>, tuning circuit <NUM> comprises tuning circuit components <NUM>.

In at least some embodiments, the sending and receiving of RF communication signals occur wirelessly and are facilitated by one or more antennas/antenna elements <NUM> and <NUM> communicatively coupled to tuning circuit <NUM>. The number of antenna elements can vary from device to device, ranging from one or more antenna elements and the presentation within UE <NUM> of a particular number (e.g., N) of antenna elements is merely for illustration.

UE <NUM> is able to wirelessly communicate with one or more base-stations, including eNB <NUM>, via one or more antennas (e.g., antennas <NUM>, <NUM>). Each of the one or more base-stations (e.g., base station <NUM>) can be any one of a number of different types of network stations and/or antennas associated with the infrastructure of the wireless network and configured to support uplink and downlink communication via one or more of the wireless communication protocols supported by a respective wireless network core, as known by those skilled in the art.

In addition to the above described hardware components of UE <NUM>, various features of the invention may be completed or supported via software or firmware code and/or logic stored within at least one of memory <NUM> and respectively executed by DSP <NUM> or processor <NUM>. Thus, for example, included within system memory <NUM> is a number of software, firmware, logic components, modules, or data, generally referenced as functional modules <NUM>, which collectively can perform or configure the UE to perform the functions described in the various UE-implemented methods presented herein.

The various components within UE <NUM> can be electrically and/or communicatively coupled together as illustrated in <FIG>. As utilized herein, the term "communicatively coupled" means that information signals are transmissible through various interconnections between the components. The interconnections between the components can be direct interconnections that include conductive transmission media which can include optical interconnects, or may be indirect interconnections that include one or more intermediate electrical components. Although certain direct interconnections are illustrated in <FIG>, it is to be understood that more, fewer or different interconnections may be present in other embodiments.

<FIG> is block diagram of an example UE <NUM> having a modem and radio frequency components including at least one tuning circuit, according to one embodiment. UE <NUM> comprises transceiver <NUM> and radio frequency front end (RFFE) module <NUM>, which is communicatively coupled to transceiver <NUM>. In addition, UE <NUM> comprises first antenna <NUM> and second antenna <NUM> which are both coupled to RFFE module <NUM>. Transceiver <NUM> comprises modem <NUM> that is in communication with a number of components within an RF receive signal path and RF transmit signal path, which components include receiver (RX) <NUM> and transmitter (TX) <NUM>. RFFE module <NUM> also includes first tuning circuit <NUM> which is communicatively coupled to an input port of RX <NUM> within the RF receive signal path. Additionally, RFFE module <NUM> includes second tuning circuit <NUM> which is communicatively coupled to an output port of TX <NUM> within the RF transmit signal path.

<FIG> illustrates an example eNB <NUM> that includes a controller <NUM>, a first transceiver <NUM> (e.g., a baseband chipset that includes a transceiver capable of communicating by radio according to a 3GPP standard), and a second transceiver <NUM>. The device further includes a memory <NUM> (in which the instructions of various signal-processing modules <NUM> are stored), a network interface <NUM> (used, for example, by the eNB <NUM> to communicate with other parts of a network <NUM>), user-input devices <NUM> (e.g., a touchscreen and a microphone), output devices <NUM> (e.g., a display and a speaker), and antennas <NUM> and <NUM>. The memory <NUM> can be implemented as volatile memory, non-volatile memory, or a combination thereof. The memory <NUM> may be implemented in multiple physical locations and across multiple types of media (e.g., dynamic random-access memory plus a hard-disk drive). The memory <NUM> can also be split among multiple hardware components. In one embodiment, each of the controller <NUM>, the first transceiver <NUM>, and the second transceiver <NUM> has a separate memory, which is collectively represented by the memory <NUM>. The controller <NUM> retrieves instructions (including those of the signal-processing modules <NUM>) from the memory <NUM> and operates according to those instructions to carry out various functions, including providing outgoing data to and receiving incoming data from the first transceiver <NUM> and the second transceiver <NUM>. Thus, when this disclosure refers to any of the signal-processing modules <NUM> carrying out an action, it is, in many embodiments, the controller <NUM> that actually carries out the action in coordination with other pieces of hardware of the device as necessary. Each of the elements of the eNB <NUM> is communicatively linked to the other elements via data pathways <NUM>. Possible implementations of the data pathways <NUM> include wires, conductive pathways on a microchip, and wireless connections. Possible implementations of the controller <NUM> include a microprocessor (such as a baseband processor), a microcontroller, a digital signal processor, and a field-programmable gate array.

In one or more embodiments, a control channel can include at least one of a Physical Downlink Control Channel (PDCCH) and an Enhanced PDDCH (EPDDCH). PDCCH can be used where control signaling from an eNodeB is received by user equipment (UE) in the first, first two, or first three, or first four symbols of a subframe, subsequently referred to as control symbols. The remaining symbols in the subframe, following the control symbols, are typically used for receiving user data. User data is received by the UE on the Physical Downlink Shared Channel (PDSCH), and in select Resource Blocks (RBs) of the PDSCH occupying either in the entire carrier bandwidth or a portion of the carrier bandwidth.

The set of PDCCH candidates to monitor are defined in terms of search spaces, where a search space <MAT> at aggregation level L ∈ {<NUM>,<NUM>,<NUM>,<NUM>} is defined by a set of PDCCH candidates. For each serving cell on which PDCCH is monitored, the control channel elements (CCEs) corresponding to a PDCCH candidate of the search space <MAT> are given by a formula taking parameters including: (i) Total number of CCEs in the control region of the subframe (derived from reduction of PCFICH and PHICH resources); (ii) Aggregation level; (iii) number of PDCCH candidates to monitor in the given search space; and (iv) slot number within the radio frame.

A physical control channel is transmitted on an aggregation of one or several consecutive CCEs, where a control channel element corresponds to nine (<NUM>) resource element groups. Each CCE is equivalent to thirty-six (<NUM>) resource elements (REs). One CCE is the minimum PDCCH allocation unit. The number of resource-element groups not assigned to PCFICH or PHICH is NREG. The CCEs available in the system are numbered from <NUM> to NCCE -<NUM>, where <MAT>. A PDCCH consisting of n consecutive CCEs may only start on a CCE fulfilling i mod n = <NUM>, where i is the CCE number.

For each serving cell, higher layer signaling can configure a UE with one or two EPDCCH-PRB-sets for EPDCCH monitoring. The PRB-pairs corresponding to an EPDCCH-PRB-set are indicated by higher layers. Each EPDCCH-PRB-set consists of a set of ECCEs numbered from <NUM> to NECCE,p,k -<NUM> where NECCE,p,k is the number of ECCEs in EPDCCH-PRB-set p of subframe k. Each EPDCCH-PRB-set can be configured for either localized EPDCCH transmission or distributed EPDCCH transmission. For each serving cell, the subframes in which the UE monitors EPDCCH UE-specific search spaces are configured by higher layers.

A UE shall monitor a set of PDCCH/EPDCCH candidates for control information, where monitoring implies attempting to decode each of the PDCCH/EPDCCH decoding candidates in the set according to the monitored downlink control information (DCI) formats. The set of PDCCH/EPDCCH candidates to monitor are defined in terms of PDCCH/EPDCCH search spaces.

To reduce latency of communication in LTE, various solutions are being studied. For example, an approach envisioned for future LTE systems is to use shorter minimum transmission time interval (TTI) (i.e., shorter than <NUM>) in UL/DL. Using a shorter minimum TTI (sTTI) allows the UE to send/receive data using reduced latency when compared to current LTE systems. In addition, acknowledging each (or a group containing few) sTTI(s) leading to faster (compared to using <NUM> TTI) acknowledging data can help in some applications such as TCP during slow-start phase for users in good channel conditions. For example, in the TCP slow-start phase for DL communication, the network-UE link capacity for a user in good channel condition can support more data; but the network sends a smaller amount of data because the network is waiting to receive the acknowledgment for the previously sent data due to the TCP slow-start phase. Therefore, faster acknowledgments (e.g., as a result of using shorter TTI length) would enable the network to better utilize the available network-UE link capacity.

For example, scheduling UE transmission over a sTTI length of <NUM> (i.e., PUSCH scheduled using a PRB spanning a <NUM> in a <NUM> subframe), or scheduling UE transmission over a sTTI length of ~<NUM> (i.e., PUSCH scheduled using a shortened PRB spanning <NUM> SC-FDMA symbols within a slot in a subframe), would not only reduce time taken to start/finish transmitting a data packet, but also potentially reduce the round trip time for possible hybrid automatic repeat request (HARQ) retransmissions related to that data packet.

The PDCCH channel carries the control information about the data being transmitted on the current subframe and the information about the resources which the UE needs to use for the uplink data. That means it is mandatory for the UE to decode the control information successfully if UE intends to send some data or receive something. For reduced latency a shortened physical downlink control channel (sPDCCH) is defined to play a similar role in a sTTI (or a group of sTTIs). For PDCCH, allocation of resources happens in terms of CCE (Control Channel Elements) which is equivalent to <NUM> Resource Elements (REs). One CCE is the minimum PDCCH allocation unit. As the sTTI length becomes smaller, the control overhead increases, which in turn increases the complexity and hence the processing delay, which could negatively impact the latency reduction offered by low-latency operation.

To reduce the control signal overhead, few general approaches are possible, including: (i) Approach <NUM>: scheduling multiple sTTIs via a single grant (e.g., sent via an sPDCCH or PDCCH/EPDCCH command) which we refer to as multi-sTTI scheduling; (ii) Approach <NUM>: sending the control information in a hierarchical manner, i.e., more than one step. For instance, a first step can provide a subset of control information common to a set of sTTIs at a first time instant, and a second step can provide complementary control information pertinent to each sTTI at a second time instant; and (iii) Approach <NUM>: sending the control information in each scheduled sTTI, but with some DCI bit field reduction compared to the DCIs used for legacy <NUM>-TTI. For instance, for <NUM>-symbol sTTI, the Resource Block Group (RBG) size can be larger (e.g., <NUM> times) than that of used for legacy <NUM>-TTI.

In addition to the above control overhead reduction techniques, to further increase the efficiency and reduce complexity of sTTI operation, the present innovation proposes to use different sPDCCH monitoring sets in different subframes based on the presence of the legacy UEs in those subframes. The eNB can exploit its knowledge regarding the usage of each subframe for legacy operation including PDCCH/EPDCCH/PDSCH/PUSCH. In particular, at the beginning of a subframe, the eNB knows how much resources are allocated to PDCCH/EPDCCH in the subframe; consequently, the eNB can indicate to a UE respective information, and the UE can monitor the corresponding monitoring sets (including search spaces) for sPDCCH operation.

In one or more embodiments, at the beginning of a <NUM>-TTI, the eNB knows whether there is any UE that is going to receive an UL/DL grant for <NUM> operation in this TTI. Exploiting this information could bring new helpful UE behaviors for UEs operating with sTTI in the subframe (e.g., in case, no <NUM>-TTI grant is sent in UE-specific search space) since:.

According to the agreements in 3GPP, from an eNB perspective, existing non-sTTI and sTTI can be Frequency Division Multiplexed (FDM) in the same subframe in the same carrier.

<FIG> illustrates a flow diagram of a method <NUM> of UE determining PDCCH assignment. Method <NUM> includes UE determining whether sTTI includes CRS (decision block <NUM>). In response to determining that sTTI includes CRS in decision block <NUM>, UE uses second set of sPDCCH control region parameters (block <NUM>). In response to determining that sTTI does not include CRS in decision block <NUM>, UE uses first set of sPDCCH control region parameters (block <NUM>). Then method <NUM> ends. Thus, UE may use different control region parameters in "cell-specific sPDCCH assignment" depending on the presence of CRS in an sTTI.

In one or more embodiments, UE monitors a set of sPDCCH candidates for control information, where monitoring implies attempting to decode each of the sPDCCHs in the set according to the monitored DCI formats. The set of sPDCCH candidates to monitor are defined in terms of sPDCCH search spaces. From a UE perspective, the sPDCCH assignment information can be based on one of the following design approaches: (<NUM>) 'cell-specific assignment' and (<NUM>) UE-specific assignment.

Cell-specific assignment is a design where 'cell-specific reservation for sPDCCH decoding candidates' will be signaled to the UE. For example, the cell-specific reservation, i.e., the information about the sPDCCH control region (e.g., the OFDM symbols carrying sPDCCH, the set of frequency resources allocated to sPDCCH) can be signaled to the UE in each subframe or in a set of subframes via dynamic physical layer signaling or via higher layer signaling. Based on a presence of a cell-specific reference signal (CRS) (or other type of signals such as DMRS, positioning reference symbols, CSI-RS, etc.) in an sTTI, the sPDCCH control region may be different in terms of bandwidth, aggregation level, etc..

'UE-specific assignment': a design where the UE is essentially only aware of its own sPDCCH decoding candidates (i.e., not other UEs sPDCCH decoding candidates) and assumes that resources other than those where the UE decodes the control channel are available for sPDSCH (i.e., a design where any 'cell-specific reservation for sPDCCH' can be transparent to the UE).

sPDCCH decoding candidate sets: The eNB may configure multiple sPDCCH monitoring sets for each UE (UE-specific assignment) or for a group of UEs (cell-specific assignment).

<FIG> illustrates a subframe <NUM> with <NUM> sTTIs, each with <NUM> symbol length. Assuming <NUM> CRS antenna ports, sTTIs <NUM>,<NUM>, and <NUM> do not contain CRS, while other sTTIs (i.e., <NUM>,<NUM>,<NUM>,<NUM>), each have <NUM> symbol containing CRS. TABLE <NUM> shows the amount of non CRS REs in a <NUM>-symbol sTTI (<NUM> CRS antenna ports) as a function of bandwidth (RBs) configured for sTTI operation.

<FIG> illustrates an example of a control channel <NUM> transmitted by an eNB indicating different control region parameters <NUM>, <NUM> for different sTTIs for instance in a subframe; as an example for subframe <NUM> <NUM>, sPDCCH control region configuration <NUM> <NUM> and in subframe <NUM> <NUM>, configuration <NUM><NUM>. It is also possible to indicate to the UE(s) which sTTIs use which sPDCCH configuration (or control region); for instance a bit-field or an index to a possible combination.

The parameters of different sets of control region can be signaled by higher layer signaling. Alternatively, the offset to the configuration where CRS (or other type of signals such as DMRS, positioning reference symbols, CSI-RS, etc.) is present in an sTTI can be fixed in specifications: e.g., In CRS containing sTTIs, sPDCCH decoding candidates with aggregation levels larger than <NUM> are not allowed, and the same number of sPDCCH decoding candidates with aggregation levels less than <NUM> exist in sTTIs with and without CRS.

For each serving cell, higher layer signaling can configure a UE with one or multiple (e.g., two) sPDCCH-PRB-sets for sPDCCH monitoring (similar to LTE EPDCCH design). Each sPDCCH-PRB-set consists of a set of shortened control channel elements (sCCEs), which are similar to the notion of CCE but tailored for sTTI with a particular TTI length. The PRB-pairs corresponding to an sPDCCH-PRB-set are indicated by higher layers (MAC or RRC) or by dynamic control signaling. An approach detailed in the following is to configure PRBs for each sPDCCH-PRB-set via higher layers, and then use dynamic signaling to indicate which sPDCCH-PRB-set(s) is to be used by the UE for sPDCCH monitoring.

For example, <FIG> illustrates a downlink channel <NUM> having four (<NUM>) PRB-sets <NUM>, <NUM>, <NUM>, <NUM> that follow a PDCCH region <NUM> for a UE that is configured by higher layer signaling. In particular, first PRB-set <NUM> is configured to include three (<NUM>) PRBs <NUM>. Second PRB-set <NUM> is configured to include three (<NUM>) PRBs <NUM>. Third PRB-set <NUM> is configured to include six (<NUM>) PRBs <NUM>. Fourth PRB-set <NUM> is configured to include nine (<NUM>) PRBs <NUM>. Then physical layer signaling (first DCI level) indicates which PRB-sets for receiving scheduling assignments to the UE should be monitored by the UE in a subframe containing multiple sTTIs (e.g., <NUM> sTTIs).

<FIG> illustrates a downlink channel <NUM> having a first subframe <NUM> and a second subframe <NUM>, each beginning with a PDCCH region <NUM> respectively. In this instance, eNB in the PDCCH region <NUM> of subframe <NUM> <NUM> can indicate first PRB-set <NUM> having three (<NUM>) PRBs <NUM> and second PRB-set <NUM> having three (<NUM>) PRBs <NUM> are to be monitored. eNB in the PDCCH region <NUM> of subframe <NUM> <NUM> can indicate that all PRB sets <NUM>, <NUM>, <NUM>, <NUM> are to be monitored, including third PRB-set <NUM> having six (<NUM>) PRBs <NUM> and fourth PRB-set <NUM> having nine (<NUM>) PRBs <NUM>. <FIG> illustrates an example of indication of different PRB-sets to be monitored by the UE for sPDCCH blind decoding from a set of configured PRB-sets for monitoring sPDCCH.

Dimensioning sPDCCH decoding candidate sets can include overlaps. <FIG> illustrates subframe <NUM> where there exist two sPDCCH-PRB-sets <NUM>, <NUM>. The second sPDCCH-PRB-set <NUM> is a subset of the first sPDCCH-PRB-set <NUM>. A UE performs blind decoding over the BD candidates of second PDCCH-PRB-set <NUM> if indicated; otherwise first sPDCCH-PRB-set <NUM> is used for control channel monitoring. Both sPDCCH-PRB-sets <NUM>, <NUM> could be configured by higher layers. Each of sPDCCH-PRB-set <NUM>, <NUM> may include sPDCCH decoding candidates that do not belong to other sets.

Dimensioning sPDCCH decoding candidate sets can include decoding candidates with smaller number of sCCE (e.g., <NUM> or <NUM>) as default decoding candidate sets. Upon receiving the set indication, decoding candidate sets with larger number of sCCE (e.g., <NUM>, and <NUM>) can also be monitored. For instance, in <FIG>, the non-overlapping part of set <NUM> may include decoding candidates with larger number of sCCEs. <FIG> is an example of BD candidates in a sTTI, where set <NUM> is a subset of set <NUM>. For set <NUM>, the whole BW can be utilized if no legacy UE is scheduled and set <NUM> can be utilized when the BW is shared between legacy and sTTI operation.

<FIG> illustrates a method <NUM> performed by the UE for monitoring sPDCCH candidates, which can be different among sTTIs or subframes. Method <NUM> includes determining whether sPDCCH set indication is decoded in the subframe (decision block <NUM>). In response to the determination in decision block <NUM> that sPDCCH set indication is decoded in the subframe, method <NUM> includes monitoring a subset of aggregation levels (block <NUM>). Then method <NUM> ends. In response to the determination in decision block <NUM> that sPDCCH set indication is not decoded in the subframe, method <NUM> includes monitoring all aggregation levels (block <NUM>). Then method <NUM> ends. For example, <FIG> illustrates a subframe <NUM> having four (<NUM>) sTTIs out of <NUM> sTTIs include one OFDM symbol containing CRS, which could limit the amount of available resources, e.g., for MBSFN and Non-MBSFN subframes. Returning to <FIG>, method <NUM> is also an example of non-overlapping part of set <NUM> that may include decoding candidates with larger number of sCCEs.

<FIG> illustrates a downlink channel <NUM> for monitoring different PRB-sets in different subframes <NUM>, <NUM>, where first subframe <NUM> has one half <NUM> of the BW allocated to legacy operation, and another half <NUM> for sTTI operation. Each subframe <NUM>, <NUM> begins with a PDCCH region <NUM> respectively. In this instance, eNB in the PDCCH region <NUM> of subframe <NUM> <NUM> can indicate first PRB-set <NUM> having three (<NUM>) PRBs <NUM> and second PRB-set <NUM> having three (<NUM>) PRBs <NUM> are to be monitored. eNB in the PDCCH region <NUM> of subframe <NUM> <NUM> can indicate that all PRB sets <NUM>, <NUM>, <NUM>, <NUM> are to be monitored, including third PRB-set <NUM> having six (<NUM>) PRBs <NUM> and fourth PRB-set <NUM> having nine (<NUM>) PRBs <NUM>. As provided, no legacy UE is scheduled in subframe <NUM>, and hence some additional PRB-sets can be used for monitoring the sPDCCH in that subframe.

<FIG> illustrates a method <NUM> for configuring CCEs based on whether any Licensed-Assist Access (LAA) small cell (Scell) is configured for any UE in the cell. Method <NUM> includes determining whether subframe is for Multicast Broadcast Single Frequency Network (MBSFN) (decision block <NUM>). In response to the determination that the subframe is MBSFN in decision block <NUM>, method <NUM> includes using sPDCCH decoding set "c" (block <NUM>). Then method <NUM> ends. In response to the determination that the subframe is not MBSFN in decision block <NUM>, method <NUM> includes further determining whether the sTTI includes CRS (decision block <NUM>). In response to the determination that the sTTI includes CRS in decision block <NUM>, method <NUM> includes using sPDCCH decoding set "b" (block <NUM>). Then method <NUM> ends. In response to the determination that the sTTI does not include CRS in decision block <NUM>, method <NUM> includes using sPDCCH decoding set "a" (block <NUM>). Then method <NUM> ends.

Method <NUM> is an example of using <NUM> symbol-OFDM sTTI. The method <NUM> provides an example showing different decoding sets can be used for different subframe and sTTI types. Set "a" for instance, can include sPDCCH candidates with lower aggregation levels (e.g., <NUM> or <NUM>) or can include smaller number of sPDCCH candidates compared to sets "b" and "c". The decoding sets can be configured for either localized sPDCCH transmission or distributed sPDCCH transmission. Also the decoding sets can be an RE-level (i.e., as a collection of REs forms an sPDCCH transmission) or an RB-level (i.e., as a collection of RBs forms an sPDCCH transmission). In case of the RB-level, it is possible to restrict having the sPDSCH corresponding to the sPDCCH not occupy REs in RBs that the sPDCCH occupies: In that case, the sPDSCH is not mapped to any physical resource-block pair(s) carrying an sPDCCH associated with the sPDSCH.

With a sPDCCH decoding candidate set indication, the PDCCH/EPDCCH can indicate which sPDCCH decoding set should be used in a subframe. With regard to transmission aspects of the sPDCCH decoding candidate set indication, eNB can indicate which sPDCCH-PRB-set(s) should be at least monitored by the UE in a subframe: (i) UE can already know candidate location(s)/size(s). For example, UE can know candidate location/s and size/s for a PDCCH candidate at a certain aggregation level L=<NUM> with the CCEs corresponding to the PDCCH candidate given by CCEs numbered <NUM>,<NUM>,<NUM>,<NUM>, which is similar to existing LTE-LAA design. In another example, the CCE numbers can be configurable to allow simultaneous operation of LAA and sTTI in a cell. A single aggregation level or multiple aggregation levels from a set of possible aggregation levels (e.g., <NUM> and <NUM>) can be used for the decoding candidate (for indicating an sPDCCH-PRB-set). The number and value of aggregation level(s) can be configurable via higher layer signaling.

<FIG> illustrates a method <NUM> for an eNB procedure to configure CCEs for monitoring a PDCCH indicating a sPDCCH decoding set. Method <NUM> includes determining whether a UE is configured for sTTI operation (decision block <NUM>). In response to the determination that the UE is not configured for sTTI operation in decision block <NUM>, method <NUM> ends. In response to the determination that the UE is configured for sTTI operation in decision block <NUM>, method <NUM> includes further determining whether LAA Scell is configured for any UE in the cell (decision block <NUM>). In response to the determination that LAA Scell is configured for any UE in the cell in decision block <NUM>, method <NUM> includes configuring first set of CCEs to be monitored for set indication. Then method <NUM> ends. In response to the determination that LAA Scell is not configured for any UE in the cell in decision block <NUM>, method <NUM> includes configuring second set of CCEs to be monitored for set indication. Then method <NUM> ends.

With further regard to transmission aspects of the sPDCCH decoding candidate set indication, eNB can indicate which sPDCCH-PRB-set(s) should be at least monitored by the UE in a subframe: (ii) will not be monitored in subframes indicated by higher layer signaling, for example, in subframes set aside for <NUM>-TTI operation only; (iii) can include DCI size similar to DCI Format 1C; (iv) can have the DCI cyclic redundancy check (CRC) scrambled by a cell-sTTI-specific RNTI. For example, all sTTI UEs in the cell (e.g., <NUM>-symbol and <NUM>) would monitor the set-indication candidate. Alternative to cell-sTTI-specific RNTI, a field in DCI can distinguish where this indication belongs to. eNB can indicate which sPDCCH-PRB-set(s) should be at least monitored by the UE in a subframe: (v) instead of a subframe level indication, a TTI-level indication is also possible, where a TTI can take any TTI value allowed in the system larger than the sTTI value the UE is configured with. For example, the UE may be configured with <NUM>-symbol-sTTI, but there could be other UEs in the cell configured with <NUM>-sTTI. As a result, the UE may be configured to monitor sPDCCH decoding set indication in each slot, as shown in <FIG>.

<FIG> illustrates a subframe <NUM> that in turn includes first slot <NUM> and second slot <NUM>. Slot-level sPDCCH that are configured for monitoring set indication that is valid for the slot duration. In the illustrated example, sTTI UEs with sTTI length of <NUM> and <NUM>-symbol would monitor slot-level set indication <NUM> in the first slot of the subframe <NUM>, However, set indication <NUM> in the second slot is only monitored by <NUM>-symbol-sTTI UEs.

One aspect provides contents/implications of a sPDCCH decoding candidate set indication. According to one embodiment, the set indication can indicate one or more of the following:.

<FIG> illustrates an example of a method <NUM> performed by the eNB to indicate the fraction for sTTI operation. Method <NUM> includes determining whether any sTTI UE is configured (decision block <NUM>). In response to determining that none of the sTTI UEs is configured in decision block <NUM>, method <NUM> includes going to next subframe (block <NUM>). Then method <NUM> ends. In response to determining that an sTTI UE is configured in decision block <NUM>, method <NUM> includes further determining whether any downlink (DL) <NUM>-ms transmission is scheduled in the current subframe (decision block <NUM>). In response to determining that any DL <NUM>-ms transmission is not scheduled in the current subframe in decision block <NUM>, method <NUM> includes setting sTTI DL resource BW fraction equal to <NUM> (block <NUM>). Then method <NUM> ends. In response to determining that a DL <NUM>-ms transmission is scheduled in the current subframe in decision block <NUM>, method <NUM> includes choosing sTTI DL resource BW fraction equal to "x" starting from resource block (RB) index "R" from a set (block <NUM>). Method <NUM> includes determining whether any uplink (UL) <NUM>-ms transmission is scheduled for a future subframe (decision block <NUM>). In response to determining that a UL <NUM>-ms transmission is scheduled for a future subframe in decision block <NUM>, method <NUM> includes choosing from a set sTTI UL resource BW fraction in subframe with "z" equal to "y" starting from RB index "R" (block <NUM>). Then method <NUM> ends. In response to determining that a UL <NUM>-ms transmission is not scheduled for a future subframe, method <NUM> includes choosing from a set sTTI UL resource BW fraction in subframe with "z" equal to <NUM> (block <NUM>). Then method <NUM> ends.

According to one alternate embodiment, which is an alternative to indicating the fraction, the fraction can be derived from the indicated sPDCCH decoding set(s). An additional offset can be signaled in the indication to UE(s) indicating where the BW for sTTI operation starts. The indication may contain a time stamp as to when the fraction of system BW for sPUSCH/SPUCCH is applied to. The eNB can send the indication when it makes a decision to schedule/not schedule any <NUM>-PUSCH/PUCCH transmissions for either of a legacy <NUM>-ms transmission or <NUM>-ms transmissions with reduced processing timing. In case of legacy <NUM>-ms transmissions, the time-stamp can be "<NUM>". In case of <NUM>-ms transmissions with reduced processing timing, the time stamp can be smaller.

From the UE perspective, the fraction of the system BW at an UL subframe for sPUSCH/sPUCCH can be based on the BW fraction indicated with the smallest time-stamp. Alternatively, the fraction can be derived based on a formula (e.g., the summation) taking into account the BW fractions given corresponding to indications sent with multiple time-stamps pointing to the same UL subframe.

<FIG> illustrates an example method <NUM> performed by an eNB to indicate a new TDD configuration for sTTI UEs inside a subframe. Method <NUM> includes determining whether any sTTI UE is configured (decision block <NUM>). In response to determining that none of the sTTI UE is configured in decision block <NUM>, method <NUM> includes going to a next subframe (block <NUM>). Then method <NUM> ends. In response to determining that an sTTI UE is configured in decision block <NUM>, method <NUM> includes determining whether any DL <NUM>-ms transmission is scheduled in the current subframe (decision block <NUM>). In response to determining that a DL <NUM>-ms transmission is not scheduled in the current subframe in decision block <NUM>, method <NUM> includes enabling a new time division duplex (TDD) configuration "T1" for sTTI UEs in the subframe (block <NUM>). Then, method <NUM> includes determining whether any UL <NUM>-ms transmission is scheduled for a future subframe "S" (decision block <NUM>). In response to determining that a UL <NUM>-ms transmission is scheduled for a future subframe "S" in decision block <NUM>, method <NUM> proceeds to the next subframe (block <NUM>). In response to determining that a UL <NUM>-ms transmission is not scheduled for a future subframe "S" in decision block <NUM>, method <NUM> includes enabling a new TDD configuration "T2" for sTTI UEs in the subframe "S" (block <NUM>). Then method <NUM> ends. In response to determining that a DL <NUM>-ms transmission is scheduled in the current subframe in decision block <NUM>, method <NUM> proceeds to decision block <NUM>.

<FIG> provides an example of related eNB procedures as detailed below. For example, in <FIG>, the indication of using decoding candidate set <NUM> may imply that there are only sTTI UEs scheduled in the current subframe, and therefore, there is no coexistence issue with legacy UEs (e.g., inside the cell), and hence using the new TDD configurations is possible. The indication can include additional information of the new TDD configuration (e.g., a location and a number of switching points).

According to one embodiment, the set indication indicates the UE behavior with respect to sPDCCH monitoring. In this embodiment, the UE can monitor a set of sPDCCH candidates on one or more activated serving cells as configured by higher layer signaling for control information, where monitoring implies attempting to decode each of the sPDCCHs in the set according to the monitored DCI formats. The set of sPDCCH candidates to monitor are defined in terms of sPDCCH UE-specific search spaces. If the UE successfully decodes the indication to which sPDCCH-PRB-sets shall be monitored, the UE shall monitor those sets; otherwise, all of the configured sPDCCH-PRB-sets (or a default set) shall be monitored as a fallback mode.

For each serving cell, the subframes in which the UE monitors sPDCCH UE-specific search spaces are configured by higher layers. The UE shall not monitor sPDCCH in subframes indicated by higher layers to decode Physical Multicast Channel (PMCH) with conditions for TDD ignored. The UE is not expected to monitor an sPDCCH candidate, if an sCCE corresponding to that sPDCCH candidate is mapped to a PRB pair that overlaps in frequency with a transmission of either a PBCH or primary or secondary synchronization signals or a PDSCH containing system information in the same subframe. The UE is not required to monitor the sPDCCH for the serving cell on which the sPDCCH is monitored in a subframe which is configured by higher layers to be part of a positioning reference signal occasion if the positioning reference signal occasion is only configured within MBSFN subframes and the cyclic prefix length used in subframe #<NUM> is the normal cyclic prefix.

Additional UE configurations for sPDCCH monitoring can be supported in one embodiment. In addition to configuring a UE to use sTTI, additional configurations which can help in managing sPDCCH monitoring can be provided. For example, a UE configured for sTTI operation in DL with sTTI length "t1" could be configured by the eNB to monitor one or more sPDCCH decoding candidates corresponding to sTTI length "t2", where t1 < t2 < <NUM>-ms. This configuration could be useful for instance to enable slot-level sPDCCH decoding set indication as shown in <FIG>. The configuration can be done, for example, via one of the following described schemes, referenced as embodiments <NUM> and <NUM>.

According to a first embodiment, the configuration includes monitoring sPDCCH candidates in a subframe in second sTTI, third sTTI, etc., with length "t2". The UE may detect a sPDCCH in an sTTI with length "t2" (referred to as t2-sPDCCH) with a DCI CRC scrambled by an sTTI-set-indication-RNTI by monitoring the following t2-sPDCCH candidate(s) according to a DCI Format (e.g., 1C). The configuration includes one t2-sPDCCH candidate at aggregation level L=<NUM> with the t2-sCCEs (corresponding to sTTI length of "t2") corresponding to the t2-sPDCCH candidate given by t2-sCCEs numbered <NUM>,<NUM>,<NUM>,<NUM>. Additional candidates with other aggregation levels are possible, e.g., another t2-sPDCCH candidate at aggregation level L=<NUM> with the t2-sCCEs corresponding to the t2-sPDCCH candidate given by t2-sCCEs numbered <NUM>,<NUM>,<NUM>,<NUM>,<NUM>,<NUM>,<NUM>,<NUM>. Information about t2-sCCEs (e.g., information about size in REs) of "t2" should be informed to the UE using sTTI with example length "t1" via higher layers. Alternatively, the sTTI length "t2" can be signaled to the UE via higher layers if the UE is capable of deriving other parameters of t2-sPDCCH (e.g., t2-sCCE) by only knowledge of "t2" itself.

According to a second embodiment, the configuration includes monitoring EPDCCH candidates with different starting symbols in the middle of the subframe. In the existing LTE specifications, it is possible to monitor EPDCCH candidates starting in the first slot and the second slot of the subframe, according to the following from 3GPP LTE Technical Specification <NUM>, Release <NUM>, "Evolved Universal Terrestrial Radio Access (E-UTRA); Physical layer procedures": For monitoring EPDCCH candidates starting in the first slot of the subframe, the starting OFDM symbol for EPDCCH given by index lEPDCCHStart in the first slot in a subframe; For monitoring EPDCCH candidates starting in the second slot of the subframe, the starting OFDM symbol for EPDCCH given by index lEPDCCHStart in the second slot in a subframe. Using EPDCCH could incur additional processing delay as the UE needs to wait till the end of the subframe to decode the EPDCCH and then start processing the sTTI, which may not be a good option.

Alternatively, in an extension of the second embodiment, special candidates in sTTIs with length "t1" (referred to here as t1-sPDCCH) in particular t1-sTTIs (sTTIs having "t1" length) in a subframe can carry the sPDCCH decoding set indication for t1-sTTIs. The information regarding those special candidates (such as aggregation level, sCCE indices, etc.) can be sent to the UE via higher layer signaling. The set indication sPDCCH DCI CRC is scrambled with sTTI-RNTI, which is a cell specific-RNTI for UEs configured with sTTI operation with length "t1". The sTTI indices in a subframe potentially carrying the set indication can be configured by higher layer signaling. Alternatively, the sTTI indices can be fixed in the specifications based on the different sTTI combinations in the cell. <FIG> illustrates special sPDCCH candidates to be used for a sPDCCH decoding set indication in known sTTI indices. For example, if a cell supports <NUM>-symbol-sTTI, <NUM>-sTTI and <NUM>-TTI, for UEs operating with <NUM>-symbol sTTI, sTTI indices <NUM> and <NUM> of subframe <NUM> may contain set indication commands <NUM>, <NUM>, as illustrated by <FIG>. <FIG> illustrates a subframe <NUM> containing <NUM>-symbol sTTIs (<NUM> CRS antenna ports).

According to one embodiment, the UE can be configured with a higher/physical layer parameter to reduce the number of blind decodes (BDs) for a specific search space at aggregation level L in an sPDCCH-PRB-set. The parameter can be the same as a "pdcch-candidateReductions" parameter. If a UE is configured with higher layer parameter for pdcch-candidateReductions for a specific search space at aggregation level L in sPDCCH-PRB-set "p" for a serving cell, the corresponding number of sPDCCH candidates is a reduced number and can be derived from a formula similar to that of an EPDCCH in existing LTE specifications. The parameter, referred to here as "spdcch-candidateReductions" can be different than the pdcch-candidateReductions parameter. The spdcch-candidateReductions parameter can be dependent on various parameters, such as sTTI length number of carriers configured for sTTI operation.

As an overall design example, an eNB configures UE1 to operate in sTTI mode with <NUM>-symbol-TTI in DL. In a subframe, if the eNB does not schedule a <NUM>-TTI DL transmission, in a known PDCCH candidate in common search space, the eNB sends a cell-specific indication, referred to herein as "Ind1" to UE1. "Ind1" contains the message that no <NUM>-ms TTI transmission is scheduled in the current subframe in this cell. Alternatively, the indication indicates which sPDCCH monitoring set to be used in the subframe is not sent when at least a <NUM>-ms TTI transmission is scheduled. If sent, the CRC is scrambled with a group-sTTI-RNTI. The group-sTTI-RNTI applies to all UEs configured for sTTI operation with any sTTI length (i.e., <NUM>-symbol and <NUM>). In every subframe where the UE1 operates with the sTTI, the UE1 monitors the PDCCH candidate to see if "Ind1" is sent.

Upon successful decoding of "Ind1", the UE monitors a set of sPDCCH candidates in the subframe, referred to as "set <NUM>". If "Ind1" is not successfully decoded (i.e., not sent or missed), the UE monitors another set of sPDCCH candidates in the subframe, referred to as "set <NUM>". Set1 and set2 are configured by higher layers. Each sPDCCH monitoring set in a subframe is associated with a set of resources (e.g., sTTI operation BW) used for sPDSCH operation. The set of resources are from among: (i) set <NUM>, referencing all the system BW; and (<NUM>) set2, referencing a configured fraction of the system BW. Once the UE successfully decodes an sPDCCH from a set of sPDCCH monitoring candidates, the UE can try to decode sPDCCH.

<FIG> illustrates a method <NUM> performed by the eNB to send the sPDCCH monitoring set indication from the network-side. Method <NUM> includes determining whether any sTTI UE is configured (decision block <NUM>). In response to determining that an sTTI UE is not configured in decision block <NUM>, method <NUM> includes going to next subframe (block <NUM>). Then method <NUM> ends. In response to determining that an sTTI UE is configured in decision block <NUM>, method <NUM> includes determining whether any DL <NUM>-ms transmission is scheduled in the current subframe (decision block <NUM>). In response to determining that a DL <NUM>-ms transmission is not scheduled in the current subframe in decision block <NUM>, method <NUM> includes setting indication to sTTI UEs (block <NUM>). Then method <NUM> ends. In response to determining that an DL <NUM>-ms transmission is scheduled in the current subframe in decision block <NUM>, method <NUM> includes proceeding to the next subframe (block <NUM>). Then method <NUM> ends.

<FIG> illustrates a method <NUM> performed within/by the UE to monitor the sPDCCH and decode the sPDSCH. Method <NUM> includes determining whether sTTI operation is allowed in the subframe (decision block <NUM>). In response to determining that sTTI operation is not allowed in the subframe in decision block <NUM>, method <NUM> includes going to next subframe (block <NUM>). Then method <NUM> ends. In response to determining that sTTI operation is allowed in the subframe in decision block <NUM>, method <NUM> includes a monitoring set indication PDCCH candidate (block <NUM>). Method <NUM> includes determining whether a set indication is decoded (decision block <NUM>). In response to determining that the set indication is not decoded in decision block <NUM>, method <NUM> includes monitoring sPDCCH candidates in set <NUM> in the subframe (block <NUM>). Method <NUM> includes decoding a sPDSCH based on resource allocation in the sPDCCH assuming a fraction of system BW (block <NUM>). Then method <NUM> ends. In response to determining that the set indication is decoded in decision block <NUM>, method <NUM> includes monitoring sPDCCH candidates in set <NUM> in the subframe (block <NUM>). Method <NUM> includes decoding a sPDSCH based on resource allocation in the sPDCCH assuming a whole system BW (block <NUM>). Then method <NUM> ends.

In summary, <FIG> illustrates downlink channels <NUM> including PDCCH <NUM> for cell-specific assignment and EPDCCH <NUM> for UE-specific assignment. The UE searches for different PDCCH /EPDCCH decoding candidates in a search-space for each candidate size in each subframe, which is referred to as aggregation level. Searching for (E)PDCCH candidate means blind decoding and checking CRC. When UE decodes the scheduling assignment, the UE can now find where the data is sent in that subframe in DL or in an associated subframe in UL. <FIG> illustrates a subframe <NUM> having EPDDCH candidate <NUM> in PRB-set <NUM> <NUM> and PRB set <NUM> <NUM>. In carrier aggregation case, the pdcch-candidateReductions parameter can be used to reduce the number of blind decoding (BD) candidates. To reduce latency, <NUM> TTI (minimum data processing unit) is changed to a smaller value (e.g., <NUM>, <NUM>-symbol). It is appreciated that a <NUM> subframe can contain multiple sTTIs (shortened TTI) as illustrated in <FIG>.

<FIG> illustrates a sPDCCH subframe <NUM> for using sTTI with reduced overhead. The sPDCCH subframe <NUM> has first DCI <NUM> and second DCIs <NUM>, <NUM> for indicating sPDSCH <NUM>, <NUM>, respectively. To schedule data in each sTTI, the sPDCCH carries scheduling assignment, controls overhead increases as TTI shortens, and controls overhead reduction schemes: As a second embodiment, the method can include sending the control information in <NUM> steps: (i) a similar step to the aforementioned steps for multiple sTTIs; and (ii) for each sTTI DCI , the UE decodes SPDSCH based on the first level and second level.

By virtue of the foregoing, a first aspect of the present innovation provides for legacy PDCCH support while accommodating sTTI with reduced overhead, as illustrated in <FIG>, where first and second DCIs can be used for sTTI UEs. In addition, if the first level is not received by the UE, the UE uses the default PRB-sets to monitor sPDCCH. For example, if in subframe <NUM>, the first level DCI is missed, the default is monitored. For example, <FIG> illustrates a downlink channel <NUM> having a first subframe <NUM> and a second subframe <NUM>, each beginning with a PDCCH region <NUM> respectively. In this instance, the eNB in the PDCCH region <NUM> of subframe <NUM> <NUM> can indicate first PRB-set <NUM> having three (<NUM>) PRBs <NUM> and second PRB-set <NUM> having three (<NUM>) PRBs <NUM> are to be monitored. These two PRB-sets <NUM>, <NUM> can represent default PRB sets <NUM>. The eNB in the PDCCH region <NUM> of subframe <NUM> <NUM> can indicate in first DCI <NUM> that an additional PRB-set <NUM> having six (<NUM>) PRBs <NUM> is to be monitored. In subframe <NUM> <NUM>, the UE can miss the first DCI and thus reverts to the default PRB-sets <NUM>, <NUM>.

In another aspect, the first level DCI for a subframe indicates: (i) a number of BD for sPDCCH in the subframe, n1; (ii) a number of BD for (E)PDCCH in the subframe, n2; and (iii) n1+n2=N, where N is fixed. As one condition, n1 and n2 can change from one subframe to another, but the sum is fixed for the two subframes. Based on n1 and n2, the UE determines the sPDCCH decoding candidates.

In an additional aspect, sTTIs of a subframe can have different sPDCCH configuration. This embodiment utilizes a same idea as with a UE-specific embodiment. Different PRB-sets can be used for different sTTIs as illustrated, for example, in <FIG>. In one or more embodiments, the configuration for an sTTI can be based on whether or not the sTTI contains CRS. <FIG> illustrates a subframe <NUM> having a first sTTI <NUM> that includes CRS, indicating that two default PRB-sets <NUM>, <NUM> should be monitored. A second sTTI <NUM> does not include CRS, indicating that PRB-sets <NUM>, <NUM>, <NUM>, <NUM> should be monitored.

In a further aspect, the eNB can send the set indication as a first DCI. For example, the eNB can send the set indication in a known location/s in a common search space. For another example, the eNB can send the set in some bit fields of the same DCI conveying LAA information. In addition to (or instead of) the first level DCI being sent at the beginning of the subframe, one embodiment includes the possibility of sending a slot-level indication valid for sTTIs belonging to a slot. <FIG> illustrates a subframe <NUM> having a slot <NUM> <NUM> having slot-level set indication valid <NUM> for four sTTIs <NUM> - <NUM> and a slot <NUM> <NUM> with slot-level set indication valid <NUM> for the identified sTTIs <NUM> - <NUM>.

<FIG> illustrates a subframe <NUM> having a slot <NUM> <NUM> having slot-level set indication valid <NUM> for four sTTIs <NUM> - <NUM> and a slot <NUM> <NUM> with slot-level set indication valid <NUM> for the identified sTTIs <NUM> - <NUM>. <FIG> further illustrates a subframe-level set indication <NUM>.

In yet an additional aspect, a new spdcch-candidateReductions parameter can be introduced which can be dependent on various parameters, such as: (i) sTTI length; (ii) a number of carriers configured for sTTI operation; and (iii) a pdcch-candidateReductions parameter. In one or more embodiments, the eNB can signal the new parameter. In one or more embodiments, the UE can determine the candidate reduction based on the above parameters.

In yet another aspect, first level DCI can indicate either implicitly or explicitly a TDD configuration to be used for the sTTIs of the subframe.

In one or more embodiments, a method performed by a UE includes receiving configuration signaling indicating a plurality of PRB-sets. The method includes detecting a first control message, the first control message transmitted in the beginning portion of a subframe. The method includes monitoring at least a second control message, where the second control message transmitted on a first PRB-set belongs to the plurality of PRB-sets in a short TTI within the subframe, and where the first PRB-set is determined using an indication in the first control message.

For example, the plurality of PRB-sets can include at least a second PRB-set in addition to the first PRB-set. The first and second PRB-sets occupy different resource block locations. For another example, the plurality of PRB-sets can include at least a second PRB-set in addition to the first PRB-set, wherein the first and second PRB-sets span a different number of resource blocks. For an additional example, the method can include determining a number of control channel monitoring candidates from the indication in the first control message; and monitoring the second control message using the determined number. For a further example, the method can include determining the first PRB-set using an indication in the first control message further comprises, determining a first subset of PRB-sets within the plurality of PRB-sets using the indication in the first control message, wherein the first set belongs to the first subset of PRB-sets. For example, assuming that the UE is configured with sets <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM> (plurality of sets), the indication can either directly identify the first set (e.g. set <NUM>) or the indication can identify a subset of sets (e.g. <NUM>, <NUM>, <NUM>).

In one or more embodiments, a method includes receiving a first indication in a first TTI, the indication indicating for the duration of the first TTI, the presence of: (i) a first number of control decoding candidates; and (ii) a second number of control decoding candidates. The method includes determining, by use of a processor: (i) a first set of control channel decoding candidates based on the first number of control decoding candidates; and (ii) a second set of control channel decoding candidates based on the second number of control decoding candidates. The method includes decoding: (i) control channel decoding candidates of the first set of control channel decoding candidates and (ii) control channel decoding candidates of the second set of control channel decoding candidates. Each control channel decoding candidate of the first set of control channel decoding candidates spans the first TTI. Each control channel decoding candidate of the second set of control channel decoding candidates spans a second TTI. The first TTI length and the second TTI length are different. The first TTI contains a set of TTIs of the second TTI length. For example, the first TTI can be a <NUM>-TTI, and the second TTI can be an sTTI.

For example, the method can include determining the configuration of control decoding candidates in each TTI of the second TTI length. The configuration includes one or more of: (i) a number of decoding candidates, and (ii) aggregation levels of the decoding candidates.

For a further example, a first subset of the set of TTIs of the second TTI length can have a first configuration of the control decoding candidates and a second subset of the set of TTIs of the second TTI length can have a second configuration of the control decoding candidates. The first and the second configurations can be different with the first subset and the second subset not overlapping.

In a particular embodiment, the method can include determining the configuration of control decoding candidates in each TTI of the second TTI length based on the presence of CRS in the TTI.

In one embodiment, the method includes receiving an indication indicating: (i) TTIs of the second TTI length belonging to the first subset; and (ii) TTIs of the second TTI length belonging to the second subset. For example, this indication could be an RRC, or could be a DCI indicating a possible set as illustrated in <FIG>.

In one embodiment, the UE can receive, via higher layers such as the RRC, a default number of first and second sets of control decoding candidates for each TTI of the first TTI duration. In a particular embodiment, if the first indication is not received, the method includes determining: (i) the first set of control channel decoding candidates based on the default first number; and (ii) the second set of control channel decoding candidates based on the default second number of control decoding candidates.

In one embodiment, the method includes receiving the first indication in a control message sent in a known set of resources with known aggregation levels. In a particular embodiment the first indication is sent in one of: (i) one PDCCH candidate at aggregation level <NUM> with the CCEs corresponding to the PDCCH candidate given by CCEs numbered <NUM>,<NUM>,<NUM>,<NUM>; and (ii) one PDCCH candidate at aggregation level <NUM> with the CCEs corresponding to the PDCCH candidate given by CCEs numbered <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>. In an exemplary embodiment, the CRC of the first indication is scrambled by CC-RNTI using the same RNTI as LAA.

In one or more embodiments, the method includes determining a TDD configuration with multiple UL/DL switching points based on the first indication.

In one or more embodiments, the method includes receiving a first indication via a higher layer for a first UE specific search space at a first aggregation level for a serving cell, the first search space corresponding to a first TTI length. The method also includes receiving a second indication via the higher layer for a second UE specific search space at a second aggregation level for a serving cell, the second search space corresponding to a second TTI length. The method further includes determining, by use of a processor: (i) a first number of control decoding candidates for the first UE specific search space; and (ii) a second number of control decoding candidates for the second UE specific search space. The first TTI length and the second TTI length are different. In a particular embodiment, the first number of control decoding candidates and the second number of control decoding candidates are determined based on one or more of the first indication, and a number of carriers configured for operation with the first TTI length and a number of carriers configured for the operation with the second TTI length.

Claim 1:
A method comprising:
receiving (<NUM>), by a user equipment, a first indication indicating a plurality of physical resource block sets;
receiving (<NUM>) a first control message in a beginning portion of a subframe, the first control message including information that indicates at least one selected physical resource block set from the plurality of physical resource block sets containing a second control message that is associated with a shortened transmission time interval;
determining (<NUM>), from the first control message, the at least one selected physical resource block set from the plurality of physical resource block sets; and
monitoring (<NUM>) the second control message in the at least one selected physical resource block set of the shortened transmission time interval, wherein the duration of the shortened transmission time interval is smaller than the duration of the subframe;
wherein:
the shortened transmission time interval is a first shortened time interval; and
the method further comprises:
monitoring the second control message using a first configuration; and
monitoring a third control message in the at least one selected physical resource block set of a second shortened transmission time interval using a second configuration;
wherein the second configuration has at least one of: (i) a different number of decoding candidates than the first configuration; (ii) a different aggregation level of the decoding candidates than the first configuration; and (iii) a different set of resource blocks than the first configuration, and
wherein the method further comprises:
identifying any common reference signals that are transmitted in the first shortened transmission time interval;
identifying any common reference signals that are transmitted in the second shortened time interval; and
associating the corresponding one of the first and second configurations based on a presence or absence of common reference signals in the first and second shortened transmission time interval.