WO2014166060A1

WO2014166060A1 - Signaling for indicating tdd ul-dl subframe configuration in lte

Info

Publication number: WO2014166060A1
Application number: PCT/CN2013/073966
Authority: WO
Inventors: Chao Wei; Neng Wang; Minghai Feng; Jilei Hou
Original assignee: Qualcomm Incorporated
Priority date: 2013-04-09
Filing date: 2013-04-09
Publication date: 2014-10-16

Abstract

Methods, systems, and devices are described for reconfiguring a user equipment (UE) to operate in a reconfigured TDD UL-DL configuration. An initial uplink- downlink (UL-DL) configuration for TDD communication may be provided for communication between a base station and a UE. One or more subframes may be identified within at least one half of each frame transmitted using the initial UL-DL configuration as flexible subframes. In one example, a reconfiguration message may be received in a first frame indicating that a transmission direction for the at least one flexible subframe of a second frame is to be changed. The reconfiguration message may include, for example, a two-bit configuration indication which indicates that the UE is to reconfigure a transmission direction for one or more flexible subframes in an associated half-subframe of a second frame.

Description

SIGNALING FOR INDICATING TDD UL-DL SUBFRAME CONFIGURATION IN LTE

BACKGROUND

[0001] The following relates generally to wireless communication, and more specifically to establishing wireless communications with base stations having preferred signal transmission configurations. Wireless communications systems are widely deployed to provide various types of communication content such as voice, video, packet data, messaging, broadcast, and so on. These systems may be multiple-access systems capable of supporting communication with multiple users by sharing the available system resources (e.g., time, frequency, and power). Examples of such multiple-access systems include code-division multiple access (CDMA) systems, time-division multiple access (TDMA) systems, frequency-division multiple access (FDMA) systems, and orthogonal frequency-division multiple access (OFDMA) systems. Additionally, some systems may operate using time-division duplex (TDD), in which a single carrier frequency is used for both uplink and downlink communications, and some systems may operate using frequency-division duplex (FDD), in which separate carrier frequencies are used for uplink and downlink communications.

[0002] In systems that operate using TDD, different formats may be used in which uplink and downlink communications may be asymmetric. TDD formats include transmission of frames of data, each including a number of different subframes in which different subframes may be uplink or downlink subframes. Reconfiguration of TDD formats may be implemented based on data traffic patterns of the particular system, in order to provide additional uplink or downlink data capacity to users of the system.

SUMMARY

[0003] The described features generally relate to one or more improved methods, systems, and/or apparatuses for wireless communication performed by a user equipment (UE) in time- division duplex (TDD) communication with a base station. In one embodiment, an initial uplink-downlink (UL-DL) configuration may be received for TDD communication with the base station. One or more subframes may be identified within at least one half of each frame transmitted using the initial UL-DL configuration as flexible subframes. In one example, a reconfiguration message may be received in a first frame indicating that a transmission direction for the at least one flexible subframe is to be changed.

[0004] In one embodiment, the reconfiguration message may include a two-bit message received in the first subframe. Receiving the reconfiguration may include receiving a first reconfiguration message in the first frame indicating that a transmission direction for at least a first flexible subframe is to be changed in the first half of the second frame. Receiving the reconfiguration message may also include receiving a second reconfiguration message in the first frame indicating that a transmission direction for at least a second flexible subframe is to be changed in the second half of the second frame. [0005] In one configuration, the first reconfiguration message may be received in a first subframe of the first frame. The second reconfiguration message may be received in a sixth subframe of the first frame.

[0006] In one example, the reconfiguration message may be received in a control channel transmission. The control channel transmission may use physical control format indicator channel (PCFICH) channel coding to encode the reconfiguration message. The reconfiguration message may include a two-bit message conveyed in a plurality of resource elements (REs) using quadrature phase shift keying (QPSK) modulation. In one embodiment, the reconfiguration message may be repeated and received in two continuous subframes.

[0007] In one configuration, the reconfiguration message may be received in a legacy control region or data region. The reconfiguration message may be received in downlink control information (DCI) from the base station. In one example, the reconfiguration message may include a two bit message included in DCI format 1, 2, 2A or 2B mapped to a UE specific search space.

[0008] In one embodiment, the reconfiguration message may be received in a downlink grant from the base station. The initial UL-DL configuration may be received in a radio resource control (RRC) message from the base station. In one example, the initial UL-DL configuration may be received in at least one system information block (SIB). The flexible subframes may be initially configured as uplink subframes.

[0009] An apparatus configured to perform time-division duplex (TDD) communications with a base station is also described. The apparatus may include means for receiving an initial uplink-downlink (UL-DL) configuration for TDD communication with the base station, and means for identifying one or more subframes within at least one half of each frame transmitted using the initial UL-DL configuration as flexible subframes. The apparatus may further include means for receiving a reconfiguration message in a first frame indicating that a transmission direction for the at least one flexible subframe is to be changed.

[0010] A device configured to perform time-division duplex (TDD) communications with a base station is also described. The device may include a processor and memory in electronic communication with the processor. Instructions may be stored in the memory. The instructions may be executable by the processor to receive an initial uplink-downlink (UL-DL) configuration for TDD communication with the base station, and identify one or more subframes within at least one half of each frame transmitted using the initial UL-DL configuration as flexible subframes. The instructions may be further executable by the processor to receive a reconfiguration message in a first frame indicating that a transmission direction for the at least one flexible subframe is to be changed.

[0011] A computer program product for performing time-division duplex (TDD) communications with a base station is also described. The computer program product may include a non-transitory computer-readable medium storing instructions executable by a processor to receive an initial uplink-downlink (UL-DL) configuration for TDD communication with the base station. The instructions may also be executable by the processor to identify one or more subframes within at least one half of each frame transmitted using the initial UL-DL configuration as flexible subframes, and receive a reconfiguration message in a first frame indicating that a transmission direction for the at least one flexible subframe is to be changed.

[0012] A method of wireless communication performed by a base station in time-division duplex (TDD) communication with a user equipment (UE) is also described. In one embodiment, an initial uplink-downlink (UL-DL) configuration for TDD communication with the UE may be determined. One or more subframes may be identified within at least one half of each frame transmitted using the initial UL-DL configuration as flexible subframes. In one example, a different UL-DL configuration may be determined to be used for TDD communication with the UE. The different UL-DL configuration may include at least one flexible subframe in which a transmission direction is to be changed. A reconfiguration message may be transmitted in a first frame indicating that the transmission direction for the at least one flexible subframe is to be changed.

[0013] In one embodiment, the reconfiguration message may include a two-bit message transmitted in the first subframe. Transmitting the reconfiguration message may include transmitting a first reconfiguration message in the first frame indicating that a transmission direction for at least a first flexible subframe is to be changed in the first half of the second frame. Transmitting the reconfiguration message may include transmitting a second reconfiguration message in the first frame indicating that a transmission direction for at least a second flexible subframe is to be changed in the second half of the second frame. In one example, the first reconfiguration message may be transmitted in a first subframe of the first frame, and the second reconfiguration message is transmitted in a sixth subframe of the first frame.

[0014] In one configuration, the reconfiguration message may be transmitted in a control channel transmission. The control channel transmission may use physical control format indicator channel (PCFICH) channel coding to encode the reconfiguration message. The reconfiguration message may be transmitted in downlink control information (DCI) to the UE. The reconfiguration message may include a two bit message included in DCI format 1, 2, 2A or 2B mapped to a UE specific search space.

[0015] In one example, the reconfiguration message may be transmitted in a downlink grant to the UE. The initial UL-DL configuration may be transmitted in a radio resource control (RRC) message to the UE.

[0016] An apparatus configured to perform time-division duplex (TDD) communications with a user equipment (UE) is also described. The apparatus may include means for determining an initial uplink-downlink (UL-DL) configuration for TDD communication with the UE, and means for identifying one or more subframes within at least one half of each frame transmitted using the initial UL-DL configuration as flexible subframes. The apparatus may further include means for determining a different UL-DL configuration is to be used for TDD communication with the UE. In one embodiment, the different UL-DL configuration may include at least one flexible subframe in which a transmission direction is to be changed. The apparatus may further include means for transmitting a reconfiguration message in a first frame indicating that the transmission direction for the at least one flexible subframe is to be changed.

[0017] A base station configured to perform time-division duplex (TDD) communications with a user equipment (UE) is also described. The base station may include a processor and memory in electronic communication with the processor. Instructions may be stored in the memory. The instructions may be executable by the processor to determine an initial uplink- downlink (UL-DL) configuration for TDD communication with the UE, and identify one or more subframes within at least one half of each frame transmitted using the initial UL-DL configuration as flexible subframes. The instructions may also be executable by the processor to determine a different UL-DL configuration is to be used for TDD communication with the UE. In one embodiment, the different UL-DL configuration may include at least one flexible subframe in which a transmission direction is to be changed. The instructions may be further executable by the processor to transmit a reconfiguration message in a first frame indicating that the transmission direction for the at least one flexible subframe is to be changed.

[0018] A computer program product for performing time-division duplex (TDD) communications with a user equipment (UE) is also described. The computer program product may include a non-transitory computer-readable medium storing instructions executable by a processor to determine an initial uplink-downlink (UL-DL) configuration for TDD communication with the UE, and identify one or more subframes within at least one half of each frame transmitted using the initial UL-DL configuration as flexible subframes. The instructions may also be executable by the processor to determine a different UL-DL configuration is to be used for TDD communication with the UE. In one embodiment, the different UL-DL configuration may include at least one flexible subframe in which a transmission direction is to be changed. The instructions may be further executable by the processor to transmit a reconfiguration message in a first frame indicating that the transmission direction for the at least one flexible subframe is to be changed.

[0019] Further scope of the applicability of the described methods and apparatuses will become apparent from the following detailed description, claims, and drawings. The detailed description and specific examples are given by way of illustration only, since various changes and modifications within the spirit and scope of the description will become apparent to those skilled in the art. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] A further understanding of the nature and advantages of the present invention may be realized by reference to the following drawings. In the appended figures, similar components or features may have the same reference label. Further, various components of the same type may be distinguished by following the reference label by a dash and a second label that distinguishes among the similar components. If only the first reference label is used in the specification, the description is applicable to any one of the similar components having the same first reference label irrespective of the second reference label.

[0021] FIG. 1 is a diagram illustrating an example of a wireless communications system in accordance with various embodiments;

[0022] FIG. 2 is a table illustrating TDD Uplink-Downlink configurations in a wireless communications system in accordance with various embodiments;

[0023] FIG. 3 illustrates a Cell Clustering Interference Mitigation environment with cells grouped according to cell clusters in accordance with various embodiments;

[0024] FIG. 4 shows a diagram of TDD frames with flexible subframes and timing of reconfiguration signaling in accordance with various embodiments;

[0025] FIG. 5 shows a table illustrating TDD Uplink-Downlink configurations and associated flexible subframes in a wireless communications system in accordance with various embodiments;

[0026] FIG. 6A shows a table illustrating flexible TDD Uplink-Downlink configurations in a wireless communications system in accordance with various embodiments;

[0027] FIG. 6B shows a table illustrating flexible TDD Uplink-Downlink configurations in a wireless communications system in accordance with various embodiments;

[0028] FIG. 6C shows a table illustrating flexible TDD Uplink-Downlink configurations in a wireless communications system in accordance with various embodiments;

[0029] FIG. 7 shows a block diagram of an example of a channel coding function in accordance with various embodiments;

[0030] FIG. 8 shows a block diagram of an example of a base station in accordance with various embodiments; [0031] FIG. 9 shows a block diagram of an example of a user equipment in accordance with various embodiments;

[0032] FIG. 10 shows a block diagram of an example of a TDD reconfiguration module in accordance with various embodiments; [0033] FIG. 11 shows a block diagram of an example of a user equipment and base station in accordance with various embodiments;

[0034] FIG. 12 is a flowchart of a method for reconfiguration of a TDD UL-DL configuration in accordance with various embodiments;

[0035] FIG. 13 is a flowchart of another method for reconfiguration of a TDD UL-DL configuration in accordance with various embodiments;

[0036] FIG. 14 is a flowchart of yet another method for reconfiguration of a TDD UL-DL configuration in accordance with various embodiments; and

[0037] FIG. 15 is a flowchart of still another method for reconfiguration of a TDD UL-DL configuration in accordance with various embodiments. DETAILED DESCRIPTION

[0038] Various aspects of the disclosure provide for reconfiguring a user equipment (UE) to operate in a reconfigured TDD UL-DL configuration. An initial uplink-downlink (UL-DL) configuration for TDD communication may be provided for communication between a base station and a UE. One or more subframes may be identified within at least one half of each frame transmitted using the initial UL-DL configuration as flexible subframes. In one example, a reconfiguration message may be received in a first frame indicating that a transmission direction for the at least one flexible subframe of a second frame is to be changed. The reconfiguration message may include, for example, a two-bit configuration indication which indicates that the UE is to reconfigure a transmission direction for one or more flexible subframes in an associated half-subframe of a second frame.

[0039] Techniques described herein may be used for various wireless communications systems such as cellular wireless systems, Peer-to-Peer wireless communications, wireless local access networks (WLANs), ad hoc networks, satellite communications systems, and other systems. The terms "system" and "network" are often used interchangeably. These wireless communications systems may employ a variety of radio communication technologies such as Code Division Multiple Access (CDMA), Time Division Multiple Access (TDMA), Frequency Division Multiple Access (FDMA), Orthogonal FDMA (OFDM A), Single-Carrier FDMA (SC-FDMA), and/or other radio technologies. Generally, wireless communications are conducted according to a standardized implementation of one or more radio communication technologies called a Radio Access Technology (RAT). A wireless communications system or network that implements a Radio Access Technology may be called a Radio Access Network (RAN).

[0040] Examples of Radio Access Technologies employing CDMA techniques include CDMA2000, Universal Terrestrial Radio Access (UTRA), etc. CDMA2000 covers IS-2000, IS-95, and IS-856 standards. IS-2000 Releases 0 and A are commonly referred to as CDMA2000 IX, IX, etc. IS-856 (TIA-856) is commonly referred to as CDMA2000 lxEV- DO, High Rate Packet Data (HRPD), etc. UTRA includes Wideband CDMA (WCDMA) and other variants of CDMA. Examples of TDMA systems include various implementations of Global System for Mobile Communications (GSM). Examples of Radio Access Technologies employing OFDM and/or OFDMA include Ultra Mobile Broadband (UMB), Evolved UTRA (E-UTRA), IEEE 802.11 (Wi-Fi), IEEE 802.16 (WiMAX), IEEE 802.20, Flash-OFDM, etc. UTRA and E-UTRA are part of Universal Mobile Telecommunication System (UMTS). 3GPP Long Term Evolution (LTE) and LTE- Advanced (LTE-A) are new releases of UMTS that use E-UTRA. UTRA, E-UTRA, UMTS, LTE, LTE-A, and GSM are described in documents from an organization named "3rd Generation Partnership Project" (3GPP). CDMA2000 and UMB are described in documents from an organization named "3rd Generation Partnership Project 2" (3GPP2). The techniques described herein may be used for the systems and radio technologies mentioned above as well as other systems and radio technologies. [0041] Thus, the following description provides examples, and is not limiting of the scope, applicability, or configuration set forth in the claims. Changes may be made in the function and arrangement of elements discussed without departing from the spirit and scope of the disclosure. Various embodiments may omit, substitute, or add various procedures or components as appropriate. For instance, the methods described may be performed in an order different from that described, and various steps may be added, omitted, or combined. Also, features described with respect to certain embodiments may be combined in other embodiments. [0042] Referring first to FIG. 1, a diagram illustrates an example of a wireless communications system 100. The system 100 includes base stations (or cells) 105, communication devices 115, and a core network 130. The base stations 105 may communicate with the communication devices 115 under the control of a base station controller (not shown), which may be part of the core network 130 or the base stations 105 in various embodiments. Base stations 105 may communicate control information and/or user data with the core network 130 through backhaul links 132. Backhaul links may be wired backhaul links (e.g., copper, fiber, etc.) and/or wireless backhaul links (e.g., microwave, etc.). In embodiments, the base stations 105 may communicate, either directly or indirectly, with each other over backhaul links 134, which may be wired or wireless communication links. The system 100 may support operation on multiple carriers (waveform signals of different frequencies). Multi-carrier transmitters can transmit modulated signals simultaneously on the multiple carriers. For example, each communication link 125 may be a multi-carrier signal modulated according to the various radio technologies described above. Each modulated signal may be sent on a different carrier and may carry control information (e.g., reference signals, control channels, etc.), overhead information, data, etc.

[0043] The base stations 105 may wirelessly communicate with the devices 115 via one or more base station antennas. Each of the base station 105 sites may provide communication coverage for a respective geographic area 110. In some embodiments, base stations 105 may be referred to as a base transceiver station, a radio base station, an access point, a radio transceiver, a basic service set (BSS), an extended service set (ESS), a NodeB, eNodeB (eNB), Home NodeB, a Home eNodeB, or some other suitable terminology. The coverage area 110 for a base station may be divided into sectors making up only a portion of the coverage area (not shown). The system 100 may include base stations 105 of different types (e.g., macro, micro, and/or pico base stations). There may be overlapping coverage areas for different technologies.

[0044] The wireless network 100 may support synchronous or asynchronous operation. For synchronous operation, the eNBs may have similar frame timing, and transmissions from different eNBs may be approximately aligned in time. For asynchronous operation, the eNBs may have different frame timing, and transmissions from different eNBs may not be aligned in time. In embodiments, some eNBs 105 may be synchronous while other eNBs may be asynchronous. [0045] The communication devices 115 are dispersed throughout the wireless network 100, and each device may be stationary or mobile. A communication device 115 may also be referred to by those skilled in the art as a mobile station, a subscriber station, a mobile unit, a subscriber unit, a wireless unit, a remote unit, a mobile device, a wireless device, a wireless communications device, a remote device, a mobile subscriber station, an access terminal, a mobile terminal, a wireless terminal, a remote terminal, a handset, a user agent, a user equipment, a mobile client, a client, or some other suitable terminology. A communication device 115 may be a cellular phone, a personal digital assistant (PDA), a wireless modem, a wireless communication device, a handheld device, a tablet computer, a laptop computer, a cordless phone, a wireless local loop (WLL) station, or the like. A communication device may be able to communicate with macro base stations, pico base stations, femto base stations, relay base stations, and the like.

[0046] The transmission links 125 shown in network 100 may include uplink (UL) transmissions from a mobile device 115 to a base station 105, and/or downlink (DL) transmissions, from a base station 105 to a mobile device 115. The downlink transmissions may also be called forward link transmissions while the uplink transmissions may also be called reverse link transmissions. In embodiments, the transmission links 125 are TDD carriers carrying bidirectional traffic within traffic frames.

[0047] In embodiments, the system 100 is an LTE/LTE-A network. In LTE/LTE-A networks, the terms evolved Node B (eNB) and user equipment (UE) may be generally used to describe the base stations 105 and communication devices 115, respectively. The system 100 may be a Heterogeneous LTE/LTE-A network in which different types of eNBs provide coverage for various geographical regions. For example, each eNB 105 may provide communication coverage for a macro cell, a pico cell, a femto cell, and/or other types of cell. A macro cell generally covers a relatively large geographic area (e.g., several kilometers in radius) and may allow unrestricted access by UEs with service subscriptions with the network provider. A pico cell would generally cover a relatively smaller geographic area and may allow unrestricted access by UEs with service subscriptions with the network provider. A femto cell would also generally cover a relatively small geographic area (e.g., a home) and, in addition to unrestricted access, may also provide restricted access by UEs having an association with the femto cell (e.g., UEs in a closed subscriber group (CSG), UEs for users in the home, and the like). An eNB for a macro cell may be referred to as a macro eNB. An eNB for a pico cell may be referred to as a pico eNB. And, an eNB for a femto cell may be referred to as a femto eNB or a home eNB. An eNB may support one or multiple (e.g., two, three, four, and the like) cells.

[0048] The communications system 100 according to an LTE/LTE-A network architecture may be referred to as an Evolved Packet System (EPS) 100. The EPS 100 may include one or more UEs 115, an Evolved UMTS Terrestrial Radio Access Network (E-UTRAN), an Evolved Packet Core (EPC) 130 (e.g., core network 130), a Home Subscriber Server (HSS), and an Operator's IP Services. The EPS may interconnect with other access networks using other Radio Access Technologies. For example, EPS 100 may interconnect with a UTRAN- based network and/or a CDMA-based network via one or more Serving GPRS Support Nodes (SGSNs). To support mobility of UEs 115 and/or load balancing, EPS 100 may support handover of UEs 115 between a source eNB 105 and a target eNB 105. EPS 100 may support intra-RAT handover between eNBs 105 and/or base stations of the same RAT (e.g., other E-UTRAN networks), and inter-RAT handovers between eNBs and/or base stations of different RATs (e.g., E-UTRAN to CDMA, etc.). The EPS 100 may provide packet- switched services, however, as those skilled in the art will readily appreciate, the various concepts presented throughout this disclosure may be extended to networks providing circuit-switched services.

[0049] The E-UTRAN may include the eNBs 105 and may provide user plane and control plane protocol terminations toward the UEs 115. The eNBs 105 may be connected to other eNBs 105 via an X2 interface (e.g., backhaul link 134). The eNBs 105 may provide an access point to the EPC 130 for the UEs 115. The eNBs 105 may be connected by an SI interface (e.g., backhaul link 132) to the EPC 130. Logical nodes within EPC 130 may include one or more Mobility Management Entities (MMEs), one or more Serving Gateways, and one or more Packet Data Network (PDN) Gateways (not shown). Generally, the MME may provide bearer and connection management. All user IP packets may be transferred through the Serving Gateway, which itself may be connected to the PDN Gateway. The PDN Gateway may provide UE IP address allocation as well as other functions. The PDN Gateway may be connected to IP networks and/or the operator's IP Services. These logical nodes may be implemented in separate physical nodes or one or more may be combined in a single physical node. The IP Networks/Operator's IP Services may include the Internet, an Intranet, an IP Multimedia Subsystem (IMS), and/or a Packet-Switched (PS) Streaming Service (PSS). [0050] The UEs 115 may be configured to collaboratively communicate with multiple eNBs 105 through, for example, Multiple Input Multiple Output (MIMO), Coordinated Multi-Point (CoMP), or other schemes. MIMO techniques use multiple antennas on the base stations and/or multiple antennas on the UE to take advantage of multipath environments to transmit multiple data streams. CoMP includes techniques for dynamic coordination of transmission and reception by a number of eNBs to improve overall transmission quality for UEs as well as increasing network and spectrum utilization. Generally, CoMP techniques utilize backhaul links 132 and/or 134 for communication between base stations 105 to coordinate control plane and user plane communications for the UEs 115. [0051] The communication networks that may accommodate some of the various disclosed embodiments may be packet-based networks that operate according to a layered protocol stack. In the user plane, communications at the bearer or Packet Data Convergence Protocol (PDCP) layer may be IP-based. A Radio Link Control (RLC) layer may perform packet segmentation and reassembly to communicate over logical channels. A Medium Access Control (MAC) layer may perform priority handling and multiplexing of logical channels into transport channels. The MAC layer may also use Hybrid ARQ (HARQ) to provide retransmission at the MAC layer to improve link efficiency. In the control plane, the Radio Resource Control (RRC) protocol layer may provide establishment, configuration, and maintenance of an RRC connection between the UE and the network used for the user plane data. At the Physical layer, the transport channels may be mapped to Physical channels.

[0052] LTE/LTE-A utilizes orthogonal frequency division multiple-access (OFDMA) on the downlink and single-carrier frequency division multiple-access (SC-FDMA) on the uplink. OFDMA and SC-FDMA partition the system bandwidth into multiple (K) orthogonal subcarriers, which are also commonly referred to as tones, bins, or the like. Each subcarrier may be modulated with data. The spacing between adjacent subcarriers may be fixed, and the total number of subcarriers (K) may be dependent on the system bandwidth. For example, K may be equal to 72, 180, 300, 600, 900, or 1200 with a subcarrier spacing of 15 kilohertz (KHz) for a corresponding system bandwidth (with guardband) of 1.4, 3, 5, 10, 15, or 20 megahertz (MHz), respectively. The system bandwidth may also be partitioned into sub- bands. For example, a sub-band may cover 1.08 MHz, and there may be 1, 2, 4, 8 or 16 sub- bands. [0053] Wireless network 100 may support operation on multiple carriers, which may be referred to as carrier aggregation (CA) or multi-carrier operation. A carrier may also be referred to as a component carrier (CC), a channel, etc. The terms "carrier," "CC," and "channel" may be used interchangeably herein. A carrier used for the downlink may be referred to as a downlink CC, and a carrier used for the uplink may be referred to as an uplink CC. A UE may be configured with multiple downlink CCs and one or more uplink CCs for carrier aggregation. An eNB may transmit data and control information on one or more downlink CCs to the UE. The UE may transmit data and control information on one or more uplink CCs to the eNB. [0054] The carriers may transmit bidirectional communications FDD (e.g., paired spectrum resources), TDD (e.g., unpaired spectrum resources). Frame structures for FDD (e.g., frame structure type 1) and TDD (e.g., frame structure type 2) may be defined. Each frame structure may have a radio frame length T_f = 3072001 T_s = 10ms and may include two half- frames of length 153600 I = 5ms each. Each half-frame may include five subframes of length 307201 = lms

[0055] For TDD frame structures, each subframe may carry UL or DL traffic, and special subframes ("S") may be used to switch between DL to UL transmission. Allocation of UL and DL subframes within radio frames may be symmetric or asymmetric and may be reconfigured semi- statically (e.g., RRC messages via backhaul, etc.). Special subframes may carry some DL and/or UL traffic and may include a Guard Period (GP) between DL and UL traffic. Switching from UL to DL traffic may be achieved by setting timing advance at the UEs without the use of Special subframes or a guard period between UL and DL subframes. UL-DL configurations with switch-point periodicity equal to the frame period (e.g., 10 ms) or half of the frame period (e.g., 5 ms) may be supported. For example, TDD frames may include one or more Special frames, and the period between Special frames may determine the TDD DL-to-UL switch-point periodicity for the frame. For LTE/LTE-A, seven different UL-DL configurations are defined that provide between 40% and 90% DL subframes as illustrated in table FIG. 2 at Table 200. As indicated in table 200, there are two switching periodicities, 5 ms and 10 ms. For configurations with 5 ms switching periodicities, there are two special subframes per frame, and for configurations with 10 ms switching periodicities there is one special subframe per frame. Some of these configurations are symmetric, having the same number of uplink and downlink subframes, while some are asymmetric, having different numbers of uplink and downlink subframes. For example, UL-DL configuration 1 is symmetric, with four uplink and four downlink subframes, UL-DL configuration 5 favors downlink throughput, and UL-DL configuration 0 favors uplink throughput.

[0056] The particular TDD UL/DL configuration that is used by a base station may be based on user requirements for the particular coverage area. For example, with reference again to FIG. 1, if a relatively large number of users in a coverage area 110 are receiving more data than they are transmitting, the UL-DL configuration for the associated base station 105 may be selected to favor downlink throughput. Similarly, if a relatively large number of users in a coverage are 110 are transmitting more data than they are receiving, the UL-DL configuration for the associated base station 105 may be selected to favor uplink throughput and the base station 105 may operate using UL-DL configuration 0. In some aspects, a base station 105 may be able to dynamically reconfigure TDD UL-DL configurations on a frame- by-frame basis. In such cases, UEs 115 that are reconfigured may receive the reconfiguration message, and transmit/receive subframes on subsequent TDD frames using the reconfigured UL-DL configuration. Such capabilities allow for relatively fast switching for the reconfigured UEs 115 according to the instantaneous traffic situation, and may provide enhanced packet throughput between the UEs 115 and base station 105. A UE 115, for example, may be in communication with a base station 105 using an initial TDD UL-DL configuration. This initial TDD UL-DL configuration, however, may become unfavorable for efficient packet throughput at a later point in time. For example, the user may switch from receiving a relatively large amount of data to transmitting a relatively large amount of data. In such a situation, a ratio of uplink to downlink transmission data may have a significant change, which may result a previously favorable UL-DL configuration becoming an unfavorable UL-DL configuration. According to various embodiments, as will be described in further detail below, a transmission direction for one or more flexible subframes within a frame may be changed using one or more reconfiguration messages.

[0057] FIG. 3 illustrates a Cell Clustering and Interference Mitigation (CCIM) environment 300 with eNBs grouped according to cell clusters. CCIM environment 200 may illustrate, for example, aspects of wireless communication system 100 illustrated in FIG. 1. Cell clusters can include one or more eNBs and eNBs within a cell cluster may be different types (e.g., macro eNB, pico eNB, femto eNB, and/or the like). As illustrated in the example of FIG. 3, CCIM environment 300 includes cell clusters 320-a, 320-b, and 320-c. Cell cluster 320-a may include eNB 105-a and eNB 105-b, cell cluster 320-b may include eNB 105-c, and cell cluster 320-c may include eNBs 105-d and 105-e. Cell clusters 320 may be statically or semi- statically defined and each eNB 105 in a cluster 320 may be aware of the other eNBs 105 of its cluster. Cell clusters 320-a, 320-b, and/or 320-c may deploy TDD carriers and TDD UL-DL configuration within each cell cluster may be synchronized. [0058] Traffic adaptation for synchronized TDD UL-DL configuration within a cell cluster may be performed by coordination of TDD UL-DL reconfiguration between cells of the cluster. Semi-static (e.g., on the order of tens of frames) TDD UL-DL reconfiguration may be performed by exchange of control-plane messaging among eNBs (e.g., via SI and/or X2 interfaces, etc.). While semi-static TDD UL-DL reconfiguration may provide adequate performance under some conditions, when traffic conditions within the cluster change rapidly, semi- static TDD UL-DL reconfiguration may result in sub-optimal allocation of UL-to-DL subframes for TDD carriers used in the cluster. In some aspects, rapidly changing traffic conditions may be accommodated through allowing the UL-DL configuration for a particular UE 115 may be reconfigured dynamically. Such dynamic reconfiguration may be transmitted to a UE 115 through signaling from the eNB 105, such as through control channel signaling, and apply to one or more subsequent TDD frames. Such reconfigurations may be accomplished according to "enhanced Interference Management and Traffic Adaptation" (elMTA), which may be implemented in some networks.

[0059] In such networks, elMTA compatible UEs may receive dynamic reconfiguration messages indicating that a transmission direction for particular subframes within a TDD frame may be changed. In some networks, the adaptation rate may be relatively fast, such as 10 ms, thus providing ability in some situations to change TDD UL-DL configurations on a frame-by- frame basis. UEs that are capable of operating according to elMTA are referred to herein as non-legacy UEs, and UEs that are not capable of operating according to elMTA are referred to herein as legacy UEs. In some situations, an eNB may be in communication with both legacy UEs and non-legacy UEs, and thus signaling between the UEs and eNB must be provided to allow the legacy UEs to operate properly while also allowing dynamic reconfiguration for non-legacy UEs as well as other related signaling to be carried out between the UEs and an eNB. An eNB operating according to elMTA may modify scheduling information for legacy UEs and dynamically reconfigure subframes in non-legacy UEs. In some aspects, a signaling mechanism is provided to signal dynamic reconfiguration to one or more UEs. [0060] In some cases, depending upon the configuration of cells, inter-cell interference may occur. For example, with continued reference to FIG. 3, cell cluster 320-c could, in some scenarios, include eNB 105-d operating according to TDD UL-DL configuration #1 (having subframe configuration DSUUDDSUUD) and eNB 105-e operating according to TDD UL- DL configuration #3 (having subframe configuration DSUUUDDDDD). In such a case, uplink transmissions for eNB 105-d in subframes 6, 7 and 8 may interfere with a downlink reception of UEs in communication with eNB 105-e. Thus, according to various embodiments, eNBs 105-d and 105-e may coordinate to reduce the likelihood of such interference. When operating according to dynamically reconfigurable TDD UL-DL configurations, according to various embodiments, dynamic and reliable signaling to indicate the TDD UL-DL configuration in a frame is provided through periodic 2-bit indications of TDD configurations that may be transmitted during each half of a TDD frame (e.g., in subframes 0 and 5), as will be described in more detail below. As indicated above, the frequency for such reconfiguration indications may be relatively high, such as every 10ms (i.e., a frame, or 10 subframes), and reliability of signaling may be important in order to prevent a UE from mistakenly decoding an indication, and hence transmit, for example, an uplink transmission by mistake. Such a situation may waste UL resources, and may also cause potentially severe interference to DL receptions of other UEs. Some methods for signaling TDD configuration may include, for example, dedicated RRC signaling that may be sent to RRC connected UEs, and may support UL-DL reconfiguration on a time scale such as two hundred milliseconds. Such signaling is relatively robust due to the use of RLC-ARQ mechanism, but may not provide the ability to dynamically adapt reconfiguration with 10ms periodicity.

[0061] Other methods of signaling TDD configuration may include broadcast signaling, which may utilize an existing control channel or a new control channel. For example, an existing physical broadcast channel (PBCH) may be used, for example by reusing currently reserved bits in a master information block (MIB). Such signaling may provide an adaptation time scale of about 40ms, and there would be 16-bit CRC protection for the signaling in accordance with existing MIB signaling. In another example, downlink control information (DCI) format 1A may be used through a common search space. In such signaling, an information field of 3 bits may be used to indicate the UL-DL subframe configuration. In some examples, a new physical downlink control channel (PDCCH) or enhanced PDCCH (ePDHCCH) transmission indicating a new UL-DL subframe configuration may cancel an existing UL-DL subframe configuration indication sent earlier. In order to reduce the overhead, common level 1 (LI) signaling may be sent only on the predefined subframes. In some instances, a UE could miss subframe configuration indication, such as when a UE is in CDRX state and assume a wrong TDD UL-DL configuration when waking up, for example. In some examples, repetition may be used to improve the reliability, but there may still be a residual missed detection rate not known by eNB, resulting in throughput loss.

[0062] In some embodiments, the present disclosure provides for reconfiguring a UE through signaling that indicates a UL-DL configuration for one or more identified flexible subframes in an identified half of a TDD frames. FIG. 4 illustrates an example 400 of signaling according to some embodiments. In the example of FIG. 4, a first frame 405 and a second frame 410 are illustrated. Within each frame 405, 410, a number of subframes may be indicated as being flexible subframes, which may be reconfigured to change transmission direction depending upon a TDD UL-DL reconfiguration message that may be provided to a UE. In this example, frame 405 includes 5 flexible subframes, including two flexible subframes 415 in a first half 405-a of the first subframe 405, and three flexible subframes 420 in a second half 405-b of the first subframe 405. Similarly, second subframe 410 includes 5 flexible subframes, including two flexible subframes 425 in a first half 410-a of the second subframe 410, and three flexible subframes 430 in a second half 410-b of the second subframe 410. In various embodiments, such as illustrated in FIG. 4, one or more of the flexible subframes 425, 430 of second frame 410 may be reconfigured through the use two- bit signaling that may be transmitted for each half-frame to indicate subframe configuration in a 5ms half-frame. In FIG. 4, the first subframe 435 (i.e., subframe 0) of first frame 405 may include signaling to indicate the transmission direction of flexible subframes 425 for the second subframe 410. Likewise, the sixth subframe 440 (i.e., subframe 5) of first frame 405 may include signaling to indicate the transmission direction of flexible subframes 430 for the second subframe 410. As mentioned the signaling transmitted during subframes 0 and 5 435, 440, may include two bits that may be mapped to UL-DL transmission directions for the associated flexible subframes 425, 430. Thus, the two-bit signaling may indicate subframe configuration of the first half frame 410-a and second half frame 410-b of the second frame 410 separately.

[0063] With reference now to FIG. 5, an example 500 of different flexible subframes for different TDD UL-DL configurations are illustrated. According to the example of FIG. 5, different subframes may be identified as flexible subframes according to the UL-DL configuration. Further, each half-frame 505, 510, may have different numbers of flexible subframes depending upon the TDD UL-DL configuration. For example, the first half 505 of the different frames may have zero, one, or two flexible subframes, depending upon the TDD UL-DL configuration. The second half 510 of the frames may have zero, one, two, or three flexible subframes, depending upon the TDD UL-DL configuration.

[0064] The mapping of the different subframe configurations according to some embodiments is illustrated in FIGS. 6A, 6B, and 6C. FIG. 6A illustrates subframe configurations 605 for half frames with three flexible subframes, such as the second half of subframes having initial TDD UL-DL configuration 0 as illustrated in FIG. 5. In this example, each identified flexible subframe may be configured for uplink transmission, indicated by signaling bits aO and al corresponding to "0 0." Likewise, signaling bits aO and al with values of "1 1" would have each identified flexible subframe configured for downlink transmission. With reference to the example of FIG. 4, bits aO and al may be transmitted in subframe 5 440 of first frame 405, which a UE may recognize, and thus reconfigure the transmission direction for flexible subframes 430 according to the mapping 605 of FIG. 6A. In a similar manner, FIG. 6B includes mapping 610 for half frames that include two flexible subframes. Such a mapping 610 may be used, for example, for the first half frame 505 for initial TDD UL-DL configurations 0, 3, and 6 illustrated in FIG. 5, as well as for the second half frames 510 for TDD UL-DL configurations 1 and 6 of FIG. 5. Likewise, FIG. 6C includes mapping 615 for half frames that include one flexible subframe. According to some embodiments, an initial TDD UL-DL configuration may be provided in system information block 1 (SIB1), and thus both UE and eNB would be aware of which mapping 605, 610, 615 would be used for particular half frame.

[0065] According to some embodiments, such two-bit subframe reconfiguration messages may be transmitted in a new control channel if broadcast signaling is required. In some embodiments, existing physical control format indicator channel (PCFICH) channel coding may be reused to encode the two-bit subframe reconfiguration messages. For example, FIG. 7 illustrates an example 700 of a channel coding function 705 that may be performed to encode two-bit subframe indicator aOal into code words 710, which may then be transmitted by a base station to a UE for reconfiguration messages. In such examples, the two-bits may be conveyed in 16 resource elements (REs) for quadrature phase shift keying (QPSK) modulation, with no CRC protection. To improve reliability, in some embodiments the same information may be repeated and transmitted in two continuous subframes. In other embodiments, two-bit subframe reconfiguration messages may be transmitted in a legacy control region or data region, similar control region reuse that may be utilized by an ePDCCH. In other embodiments, resources utilized by a new channel may puncture REs of other channels for legacy UEs; while non-legacy UEs may rate match around the REs of the new channel. In further examples, two-bit subframe reconfiguration messages may also utilize an existing DCI format if the signaling is only required for specific UE. In still further examples, an information field of two-bits may be added into a downlink grant in the form of PDCCH or ePDCCH. The presence of the additional field may be configured, for example, via RRC signaling only for UEs supporting dynamic reconfiguration, and it may not increase number of PDCCH decodes. Furthermore, some embodiments provide the two-bit message only to DCI format 1, 2, 2A and 2B, mapped only to UE specific search space, thus eliminating a need for zero padding. In embodiments that utilize DCI signaling, CRC protection may be provided and thus false alarms from signaling error may be reduced. Moreover, the eNB could know whether UE receives the subframe indicator successfully based on received ACK feedback of the corresponding PDSCH. The modified DCI format according to embodiments may also provide enhanced flexibility for an eNB to schedule UE in flexible subframes for DL transmission.

[0066] Thus, in order to provide reconfiguration signaling and dynamic resource allocation in elMTA systems, various aspects of the present disclosure provide for transmission of information related to the maximum and minimum number of uplink subframes that may be configured for TDD frames according to different initial TDD UL-DL configurations, as well as reconfiguration messages indicating particular subframes that are to be changed from uplink to downlink, or downlink to uplink. FIG. 8 shows a block diagram of a communications system 800 that may be configured for reconfiguration of TDD UL-DL configuration. This system 800 may be an example of aspects of the system 100 depicted in FIG. 1, or system 300 of FIG. 3. System 800 may include a base station 105-f. The base station 105-f may include antenna(s) 845, a transceiver module 850, memory 870, and a processor module 860, which each may be in communication, directly or indirectly, with each other (e.g., over one or more buses 880). The transceiver module 850 may be configured to communicate bi-directionally, via the antenna(s) 845, with UE devices 115-a, 115-b. The transceiver module 850 (and/or other components of the base station 105-f) may also be configured to communicate bi-directionally with one or more networks. In some cases, the base station 105-f may communicate with the core network 130-a through network communications module 865. Base station 105-f may be an example of an eNodeB base station, a Home eNodeB base station, a NodeB base station, and/or a Home NodeB base station.

[0067] Base station 105-f may also communicate with other base stations 105, such as base station 105-m and base station 105-n. In some cases, base station 105-f may communicate with other base stations such as 105-m and/or 105-n utilizing base station communication module 815. In some embodiments, base station communication module 815 may provide an X2 interface within an LTE wireless communication technology to provide communication between some of the base stations 105. In some embodiments, base station 105-f may communicate with other base stations through core network 130-a.

[0068] The memory 870 may include random access memory (RAM) and read-only memory (ROM). The memory 870 may also store computer-readable, computer-executable software code 875 containing instructions that are configured to, when executed, cause the processor module 860 to perform various functions described herein (e.g., TDD UL-DL reconfiguration, determination and transmission of reconfiguration messages, etc.). Alternatively, the software code 875 may not be directly executable by the processor module 860 but be configured to cause the processor, e.g., when compiled and executed, to perform functions described herein.

[0069] The processor module 860 may include an intelligent hardware device, e.g., a central processing unit (CPU), a microcontroller, an application- specific integrated circuit (ASIC), etc. The transceiver module(s) 850 may include a modem configured to modulate the packets and provide the modulated packets to the antenna(s) 845 for transmission, and to demodulate packets received from the antenna(s) 845. While some examples of the base station 105-f may include a single antenna 845, the base station 105-f may include multiple antennas 845 for multiple links which may support carrier aggregation. For example, one or more links may be used to support macro communications with UE devices 115-a, 115-b.

[0070] According to the architecture of FIG. 8, the base station 105-f may further include a communications management module 840. The communications management module 840 may manage communications with other base stations 105. By way of example, the communications management module 840 may be a component of the base station 105-f in communication with some or all of the other components of the base station 105-f via a bus 880. Alternatively, functionality of the communications management module 840 may be implemented as a component of the transceiver module 850, as a computer program product, and/or as one or more controller elements of the processor module 860.

[0071] In some embodiments, the transceiver module 850 in conjunction with antenna(s) 845, along with other possible components of base station 105-f, may determine TDD UL- DL configurations for various UEs communicating with the base station 105-f, and also determine uplink resources for non-legacy UEs that may be reconfigured with different TDD UL-DL configurations. In some embodiments, base station 105-f includes a TDD UL-DL configuration selection module 820 that determines a TDD UL-DL configuration for UEs 115-a, 115-b. As discussed above, in some aspects different UEs 115-a, 115-b, may include legacy UEs and non-legacy UEs, and TDD UL-DL configuration module 820 may determine UL-DL configurations for both legacy and non-legacy UEs. In the embodiment of FIG. 8, UE 115-a may be a legacy UE, and UE 115-b may be a non-legacy UE. The TDD UL-DL configuration for legacy UE 115-a may be transmitted via SIBl using TDD UL-DL configuration transmission module 825, in conjunction with transceiver module(s) 850. Likewise, an initial TDD UL-DL configuration for non-legacy UE 115-b may be transmitted using SIBl, using TDD UL-DL configuration transmission module 825 in conjunction with transceiver module(s) 850. TDD UL-DL configuration selection module 820 may also periodically determine that the default TDD UL-DL configuration for legacy UE 115-a is to be changed, in which case updated SIBl blocks may be transmitted using TDD UL-DL configuration transmission module 825, in conjunction with transceiver module(s) 850. The TDD UL-DL configuration module also, in some embodiments, may generate one or more messages that indicate the flexible subframes that may be configured for non-legacy UE 115- b. Such messages may be transmitted to the UEs 115 using the TDD UL-DL configuration transmission module 825. In some examples, an identification of the flexible subframes may be provided through a bitmap transmitted to the UE, or through other indication in an RRC message, and the identification of the flexible subframes may be determined based on the TDD UL-DL configuration provided in the SIB message. In some examples, an identification of the flexible subframes may be determined based on a second semi-static TDD UL-DL configuration transmitted to the UE in an RRC message. [0072] At some point, traffic patterns may change such than an initial TDD UL-DL configuration is not optimal for one or more UEs 115-a and 115-b. In the case of non-legacy UE 115-b, UL-DL reconfiguration determination module 830 may determine that the UL-DL configuration for non-legacy UE 115-b is to be reconfigured to a different UL-DL configuration. For example, changes in traffic between the base station 105-f and non-legacy UE 115-b may change such that additional data is to be transmitted to non-legacy UE 115-b, in which case UL-DL reconfiguration determination module 830 may determine that non- legacy UE 115-b is to be reconfigured to operate according to a different UL-DL configuration. Reconfiguration information may be provided to UL-DL reconfiguration transmission module 835, which may transmit TDD UL-DL reconfiguration messages, in conjunction with transceiver module(s) 850, to the UE 115-b. In some embodiments, the UL- DL reconfiguration determination module 830 may generate two-bit reconfiguration messages that may be transmitted for an identified half frame to the UE 115-b to notify the UE 115-b that a transmission direction of one or more particular subframes is to be changed. UL-DL reconfiguration transmission module 835 may transmit such reconfiguration message in conjunction with transceiver module(s) 850, to the UE 115-b. As mentioned above, such a reconfiguration message may be mapped to a predefined identification of subframe transmission directions. [0073] According to some examples, a base station may determine the TDD UL-DL configuration and reconfiguration associated with a UE, and also transmit information related to configuration and reconfiguration that the UE is to use for communication with the base station. The UE will receive this information, switch to the new TDD UL-DL configuration as indicated by reconfiguration messages. With reference now to FIG. 9, an example wireless communication system 900 that performs TDD UL/DL reconfigurations is depicted. System 900 includes a UE 115-c that may communicate with base station 105-g to receive access to one or more wireless networks, and may be an example of aspects of the system 90 of FIG. 1, system 300 of FIG. 3, or system 800 of FIG. 8. UE 115-c may be an example of a user equipment 115 of FIGS. 1, 3, or 5. UE 115-c, includes one or more antenna(s) 905 communicatively coupled to receiver module(s) 910 and transmitter module(s) 915, which are in turn communicatively coupled to a control module 920. Control module 920 includes one or more processor module(s) 925, a memory 930 that may include software 935, and a TDD reconfiguration module 940. The software 935 may be for execution by processor module 925 and/or TDD reconfiguration module 940. [0074] The processor module(s) 925 may include an intelligent hardware device, e.g., a central processing unit (CPU), a microcontroller, an application specific integrated circuit (ASIC), etc. The memory 930 may include random access memory (RAM) and read-only memory (ROM). The memory 930 may store computer-readable, computer-executable software code 935 containing instructions that are configured to, when executed (or when compiled and executed), cause the processor module 925 and/or TDD reconfiguration module 940 to perform various functions described herein. The TDD reconfiguration module 940 may be implemented as a part of the processor module(s) 925, or may be implemented using one or more separate CPUs or ASICs, for example. The transmitter module(s) 915 may transmit to base station 105-g (and/or other base stations) to establish communications with one or more wireless communications networks (e.g., E-UTRAN, UTRAN, etc.), as described above. The TDD reconfiguration module 940 may be configured to receive TDD reconfiguration messages from base station 105-g and change a TDD UL-DL configuration for flexible subframes of a following frame based on the received messages, such as based on the receipt of a two-bit indication of configuration mapped to a particular configuration for identified flexible subframes. The TDD reconfiguration module 940 may also be configured to receive information related to the identification of flexible subframes for different TDD UL-DL configurations as well as mappings between two bit reconfiguration messages and UL-DL direction of associated flexible subframes, such as provided in examples as described above. The receiver module(s) 910 may receive downlink transmissions from base station 105-g (and/or other base stations), such as described above. Downlink transmissions are received and processed at the user equipment 115-c. The components of UE 115-c may, individually or collectively, be implemented with one or more Application Specific Integrated Circuits (ASICs) adapted to perform some or all of the applicable functions in hardware. Each of the noted modules may be a means for performing one or more functions related to operation of the UE 115-c.

[0075] FIG. 10 illustrates an example of a TDD reconfiguration module 940-a, which includes a TDD UL-DL configuration determination module 1005, a UL-DL reconfiguration determination module, 1010, and a mapping module 1015. The TDD UL-DL configuration determination module 1005 may receive TDD UL-DL configuration information from a base station, and set the TDD UL-DL configuration according to the information. This information may be received through a system information block (e.g., SIB1), or may be received through one or more reconfiguration messages received from the base station in accordance with elMTA, for example. The TDD UL-DL configuration information may also include information related to flexible subframes, which may be used to determine transmission direction for reconfigured subframes. The UL-DL reconfiguration determination module 1010 may receive reconfiguration messages, such two-bit reconfiguration messages, and determine that one or more flexible subframes are to be reconfigured, such as described above. Mapping module 1015 may receive and store different mappings between reconfiguration messages and uplink/downlink configurations of associated flexible subframes. The components of TDD reconfiguration module 940-a may, individually or collectively, be implemented with one or more ASICs adapted to perform some or all of the applicable functions in hardware. Each of the noted modules may be a means for performing one or more functions related to operation of the TDD reconfiguration module 940-a.

[0076] FIG. 11 is a block diagram of a system 1100 including a base station 105-h and a mobile device 115-d. This system 1100 may be an example of the system 100 of FIGS. 1, system 300 of FIG. 3, system 800 of FIG. 8, or system 1000 of FIG. 10. The base station 105-h may be equipped with antennas 1134-a through 1134-x, and the mobile device 115-d may be equipped with antennas 1152-a through 1152-n. At the base station 105-h, a transmit processor 1120 may receive data from a data source. [0077] The transmit processor 1120 may process the data. The transmit processor 1120 may also generate reference symbols, and a cell-specific reference signal. A transmit (TX) MEVIO processor 1130 may perform spatial processing (e.g., precoding) on data symbols, control symbols, and/or reference symbols, if applicable, and may provide output symbol streams to the transmit modulators 1132-a through 1132-x. Each modulator 1132 may process a respective output symbol stream (e.g., for OFDM, etc.) to obtain an output sample stream. Each modulator 1132 may further process (e.g., convert to analog, amplify, filter, and upconvert) the output sample stream to obtain a downlink (DL) signal. In one example, DL signals from modulators 1132-a through 1132-x may be transmitted via the antennas 1134-a through 1134-x, respectively according to a particular TDD Uplink/Downlink configuration.

[0078] At the mobile device 115-d, the mobile device antennas 1152-a through 1152-n may receive the DL signals according to the particular TDD Uplink/Downlink configuration from the base station 105-h and may provide the received signals to the demodulators 1154-a through 1154-n, respectively. Each demodulator 1154 may condition (e.g., filter, amplify, downconvert, and digitize) a respective received signal to obtain input samples. Each demodulator 1154 may further process the input samples (e.g., for OFDM, etc.) to obtain received symbols. A MIMO detector 1156 may obtain received symbols from all the demodulators 1154-a through 1154-n, perform MIMO detection on the received symbols if applicable, and provide detected symbols. A receive processor 1158 may process (e.g., demodulate, deinterleave, and decode) the detected symbols, providing decoded data for the mobile device 115-d to a data output, and provide decoded control information to a processor 1180, or memory 1182. The processor 1180 may be coupled with a TDD reconfiguration module 1184 that may reconfigure the TDD UL-DL configuration of mobile device 115-d according to a received reconfiguration message, such as described above. The processor 1180 may perform frame formatting according to a current TDD UL/DL configuration, and may thus flexibly configure the TDD UL/DL frame structure based on the current UL/DL configuration of the base station 105-h.

[0079] On the uplink (UL), at the mobile device 115-d, a transmit processor 1164 may receive and process data from a data source. The transmit processor 1164 may also generate reference symbols for a reference signal. The symbols from the transmit processor 1164 may be precoded by a transmit MIMO processor 1166 if applicable, further processed by the demodulators 1154-a through 1154-n (e.g., for SC-FDMA, etc.), and be transmitted to the base station 105-h in accordance with the transmission parameters received from the base station 105-h. At the base station 105-h, the UL signals from the mobile device 115-d may be received by the antennas 1134, processed by the demodulators 1132, detected by a MIMO detector 1136 if applicable, and further processed by a receive processor 1138. The receive processor 1138 may provide decoded data to a data output and to the processor 1140. A memory 1142 may be coupled with the processor 1140. The processor 1140 may perform frame formatting according to a current TDD UL/DL configuration. A TDD UL/DL configuration module 1144 may, in some embodiments, configure or reconfigure the base station 105-h, or one or more carriers of the base station 105-h, to operate according to different TDD UL/DL configurations, and transmit reconfiguration messages for reconfigured UL-DL configurations to mobile device 115-d, such as described above. Similarly as discussed above, system 1100 may support operation on multiple component carriers, each of which include waveform signals of different frequencies that are transmitted between base station 105-h and devices 115-d. Multiple component carriers may carry uplink and downlink transmissions between mobile device 115-d and base station 105-h, and base station 105-h may support operation on multiple component carriers that may each have different TDD configurations. In some embodiments, the TDD UL/DL configuration module 1144 may dynamically reconfigure the TDD UL/DL configuration of base station 105-h carriers according to real-time or near real-time communications through the base station 105-h. The components of the mobile device 115-d may, individually or collectively, be implemented with one or more Application Specific Integrated Circuits (ASICs) adapted to perform some or all of the applicable functions in hardware. Each of the noted modules may be a means for performing one or more functions related to operation of the system 1100. Similarly, the components of the base station 105-h may, individually or collectively, be implemented with one or more Application Specific Integrated Circuits (ASICs) adapted to perform some or all of the applicable functions in hardware. Each of the noted components may be a means for performing one or more functions related to operation of the system 1100. [0080] FIG. 12 illustrates a method 1200 that may be carried out by a UE in a wireless communications system according to various embodiments. The method 1200 may, for example, be performed by a UE of FIG. 1, 3, 8, 9, or 11, or using any combination of the devices described for these figures. Initially, at block 1205, the UE receives an initial uplink- downlink (UL-DL) configuration for TDD communication with the base station. At block 1210, the UE identifies one or more subframes within at least one-half of each frame transmitted using the initial UL-DL configuration as flexible subframes. Finally, at block 1215, the UE receives a reconfiguration message in a first frame indicating that a transmission direction for the at least one flexible subframe is to be changed. The reconfiguration message may include, for example, a two-bit reconfiguration message such as described above.

[0081] FIG. 13 illustrates another method 1300 that may be carried out by a base station in a wireless communications system according to various embodiments. The method 1300 may, for example, be performed by a base station of FIG. 1, 3, 8, 9, or 11, or using any combination of the devices described for these figures. Initially, at block 1305, the UE receives an initial uplink-downlink (UL-DL) configuration for TDD communication with the base station. At block 1310, the UE identifies one or more subframes within at least one-half of each frame transmitted using the initial UL-DL configuration as flexible subframes. Such an identification may be provided to the UE by the base station, for example, and may then be used for subsequent reconfiguration of transmission direction for flexible subframes. At block 1315, UE receives a first reconfiguration message in the first frame indicating that a transmission direction for at least a first flexible subframe is to be changed in the first half of the second frame. Finally, at block 1320, the UE receives a second reconfiguration message in the first frame indicating that a transmission direction for at least a second flexible subframe is to be changed in the second half of the second frame.

[0082] FIG. 14 illustrates a method 1400 that may be carried out by a base station in a wireless communications system according to various embodiments. The method 1400 may, for example, be performed by a base station of FIG. 1, 3, 8, 9, or 11, or using any combination of the devices described for these figures. Initially, at block 1405, the base station determines an initial uplink-downlink (UL-DL) configuration for TDD communication with the UE. At block 1410, the base station identifies one or more subframes within at least one half of each frame transmitted using the initial UL-DL configuration as flexible subframes. Such an identification may be provided to the UE, and may then be used for subsequent reconfiguration of transmission direction for flexible subframes. At block 1415, the base station determines a different UL-DL configuration is to be used for TDD communication with the UE, the different UL-DL configuration comprising at least one flexible subframe in which a transmission direction is to be changed. Finally, at block 1420, the base station transmits a reconfiguration message in a first frame indicating that the transmission direction for the at least one flexible subframe is to be changed. The reconfiguration message may include, for example, a two-bit reconfiguration message such as described above.

[0083] FIG.15 illustrates another method 1500 that may be carried out by a base station in a wireless communications system according to various embodiments. The method 1500 may, for example, be performed by a base station of FIG. 1, 3, 8, 9, or 11, or using any combination of the devices described for these figures. Initially, at block 1505, the base station determines an initial uplink-downlink (UL-DL) configuration for TDD communication with the UE. At block 1510, the base station identifies one or more subframes within at least one half of each frame transmitted using the initial UL-DL configuration as flexible subframes. Such an identification may be provided to the UE, and may then be used for subsequent reconfiguration of transmission direction for flexible subframes. At block 1515, the base station determines a different UL-DL configuration is to be used for TDD communication with the UE, the different UL-DL configuration comprising at least one flexible subframe in which a transmission direction is to be changed. At block 1520, the base station transmits a first reconfiguration message in the first frame indicating that a transmission direction for at least a first flexible subframe is to be changed in the first half of the second frame. Finally, at block 1525, the base station transmits a second reconfiguration message in the first frame indicating that a transmission direction for at least a second flexible subframe is to be changed in the second half of the second frame.

[0084] The detailed description set forth above in connection with the appended drawings describes exemplary embodiments and does not represent the only embodiments that may be implemented or that are within the scope of the claims. The term "exemplary" used throughout this description means "serving as an example, instance, or illustration," and not "preferred" or "advantageous over other embodiments." The detailed description includes specific details for the purpose of providing an understanding of the described techniques. These techniques, however, may be practiced without these specific details. In some instances, well-known structures and devices are shown in block diagram form in order to avoid obscuring the concepts of the described embodiments.

[0085] Information and signals may be represented using any of a variety of different technologies and techniques. For example, data, instructions, commands, information, signals, bits, symbols, and chips that may be referenced throughout the above description may be represented by voltages, currents, electromagnetic waves, magnetic fields or particles, optical fields or particles, or any combination thereof.

[0086] The various illustrative blocks and modules described in connection with the disclosure herein may be implemented or performed with a general-purpose processor, a digital signal processor (DSP), an application specific integrated circuit (ASIC), a field programmable gate array (FPGA) or other programmable logic device, discrete gate or transistor logic, discrete hardware components, or any combination thereof designed to perform the functions described herein. A general-purpose processor may be a microprocessor, but in the alternative, the processor may be any conventional processor, controller, microcontroller, or state machine. A processor may also be implemented as a combination of computing devices, e.g., a combination of a DSP and a microprocessor, multiple microprocessors, one or more microprocessors in conjunction with a DSP core, or any other such configuration.

[0087] The functions described herein may be implemented in hardware, software executed by a processor, firmware, or any combination thereof. If implemented in software executed by a processor, the functions may be stored on or transmitted over as one or more instructions or code on a computer-readable medium. Other examples and implementations are within the scope and spirit of the disclosure and appended claims. For example, due to the nature of software, functions described above can be implemented using software executed by a processor, hardware, firmware, hardwiring, or combinations of any of these. Features implementing functions may also be physically located at various positions, including being distributed such that portions of functions are implemented at different physical locations. Also, as used herein, including in the claims, "or" as used in a list of items prefaced by "at least one of indicates a disjunctive list such that, for example, a list of "at least one of A, B, or C" means A or B or C or AB or AC or BC or ABC (i.e., A and B and C).

[0088] Computer-readable media includes both computer storage media and communication media including any medium that facilitates transfer of a computer program from one place to another. A storage medium may be any available medium that can be accessed by a general purpose or special purpose computer. By way of example, and not limitation, computer-readable media can comprise RAM, ROM, EEPROM, CD-ROM or other optical disk storage, magnetic disk storage or other magnetic storage devices, or any other medium that can be used to carry or store desired program code means in the form of instructions or data structures and that can be accessed by a general -purpose or special- purpose computer, or a general-purpose or special-purpose processor. Also, any connection is properly termed a computer-readable medium. For example, if the software is transmitted from a website, server, or other remote source using a coaxial cable, fiber optic cable, twisted pair, digital subscriber line (DSL), or wireless technologies such as infrared, radio, and microwave, then the coaxial cable, fiber optic cable, twisted pair, DSL, or wireless technologies such as infrared, radio, and microwave are included in the definition of medium. Disk and disc, as used herein, include compact disc (CD), laser disc, optical disc, digital versatile disc (DVD), floppy disk and blu-ray disc where disks usually reproduce data magnetically, while discs reproduce data optically with lasers. Combinations of the above are also included within the scope of computer-readable media.

[0089] The previous description of the disclosure is provided to enable a person skilled in the art to make or use the disclosure. Various modifications to the disclosure will be readily apparent to those skilled in the art, and the generic principles defined herein may be applied to other variations without departing from the spirit or scope of the disclosure. Throughout this disclosure the term "example" or "exemplary" indicates an example or instance and does not imply or require any preference for the noted example. Thus, the disclosure is not to be limited to the examples and designs described herein but is to be accorded the widest scope consistent with the principles and novel features disclosed herein. [0090] What is claimed is:

Claims

1. A method of wireless communication performed by a user equipment (UE) in time-division duplex (TDD) communication with a base station, comprising:

receiving an initial uplink-downlink (UL-DL) configuration for TDD communication with the base station;

identifying one or more subframes within at least one-half of each frame transmitted using the initial UL-DL configuration as flexible subframes; and

receiving a reconfiguration message in a first frame indicating that a transmission direction for the at least one flexible subframe is to be changed.

2. The method of claim 1, wherein the reconfiguration message comprises a two-bit message received in the first subframe.

3. The method of claim 2, wherein the receiving comprises: receiving a first reconfiguration message in the first frame indicating that a transmission direction for at least a first flexible subframe is to be changed in the first half of the second frame; and

receiving a second reconfiguration message in the first frame indicating that a transmission direction for at least a second flexible subframe is to be changed in the second half of the second frame.

4. The method of claim 3, wherein the first reconfiguration message is received in a first subframe of the first frame, and the second reconfiguration message is received in a sixth subframe of the first frame.

5. The method of claim 1, wherein the reconfiguration message is received in a control channel transmission.

6. The method of claim 5, wherein the control channel transmission physical control format indicator channel (PCFICH) channel coding to encode reconfiguration message.

7. The method of claim 6, wherein the reconfiguration message comprises a two-bit message conveyed in a plurality of resource elements (REs) using quadrature phase shift keying (QPSK) modulation.

8. The method of claim 6, wherein the reconfiguration message is repeated and received in two continuous subframes.

9. The method of claim 1, wherein the reconfiguration message is received in a legacy control region or data region.

10. The method of claim 1, wherein the reconfiguration message is received in downlink control information (DCI) from the base station.

11. The method of claim 10, wherein the reconfiguration message comprises a two bit message included in DCI format 1, 2, 2A or 2B mapped to a UE specific search space.

12. The method of claim 1, wherein the reconfiguration message is received in a downlink grant from the base station.

13. The method of claim 1, wherein the initial UL-DL configuration is received in a radio resource control (RRC) message from the base station.

14. The method of claim 13, wherein the initial UL-DL configuration is received in at least one system information block (SIB).

15. The method of claim 1, wherein the flexible subframes are initially configured as uplink subframes.

16. An apparatus configured to perform time-division duplex (TDD) communications with a base station, comprising:

means for receiving an initial uplink-downlink (UL-DL) configuration for TDD communication with the base station;

means for identifying one or more subframes within at least one half of each frame transmitted using the initial UL-DL configuration as flexible subframes; and

means for receiving a reconfiguration message in a first frame indicating that a transmission direction for the at least one flexible subframe is to be changed.

17. The apparatus of claim 16, wherein the reconfiguration message comprises a two-bit message received in the first subframe.

18. The apparatus of claim 17, wherein the means for receiving the reconfiguration message comprises:

means for receiving a first reconfiguration message in the first frame indicating that a transmission direction for at least a first flexible subframe is to be changed in the first half of the second frame; and

means for receiving a second reconfiguration message in the first frame indicating that a transmission direction for at least a second flexible subframe is to be changed in the second half of the second frame.

19. The apparatus of claim 18, wherein the first reconfiguration message is received in a first subframe of the first frame, and the second reconfiguration message is received in a sixth subframe of the first frame.

20. The apparatus of claim 16, wherein the reconfiguration message is received in a control channel transmission.

21. The apparatus of claim 20, wherein the control channel transmission uses physical control format indicator channel (PCFICH) channel coding to encode the reconfiguration message.

22. The apparatus of claim 21, wherein the reconfiguration message comprises a two-bit message conveyed in a plurality of resource elements (REs) using quadrature phase shift keying (QPSK) modulation.

23. The apparatus of claim 21, wherein the reconfiguration message is repeated and received in two continuous subframes.

24. The apparatus of claim 16, wherein the reconfiguration message is received in a legacy control region or data region.

25. The apparatus of claim 16, wherein the reconfiguration message is received in downlink control information (DCI) from the base station.

26. The apparatus of claim 25, wherein the reconfiguration message comprises a two bit message included in DCI format 1, 2, 2A or 2B mapped to a UE specific search space.

27. The apparatus of claim 16, wherein the reconfiguration message is received in a downlink grant from the base station.

28. The apparatus of claim 16, wherein the initial UL-DL configuration is received in a radio resource control (RRC) message from the base station.

29. The apparatus of claim 28, wherein the initial UL-DL configuration is received in at least one system information block (SIB).

30. The apparatus of claim 16, wherein the flexible subframes are initially configured as uplink subframes.

31. A device configured to perform time-division duplex (TDD) communications with a base station, comprising:

a processor;

memory in electronic communication with the processor; and

instructions stored in the memory, the instructions being executable by the processor to:

receive an initial uplink-downlink (UL-DL) configuration for TDD communication with the base station;

identify one or more subframes within at least one half of each frame transmitted using the initial UL-DL configuration as flexible subframes; and

receive a reconfiguration message in a first frame indicating that a transmission direction for the at least one flexible subframe is to be changed.

32. A computer program product for performing time-division duplex (TDD) communications with a base station, the computer program product comprising a non- transitory computer-readable medium storing instructions executable by a processor to:

receive an initial uplink-downlink (UL-DL) configuration for TDD communication with the base station; identify one or more subframes within at least one half of each frame transmitted using the initial UL-DL configuration as flexible subframes; and

33. A method of wireless communication performed by a base station in time-division duplex (TDD) communication with a user equipment (UE), comprising:

determining an initial uplink-downlink (UL-DL) configuration for TDD communication with the UE;

identifying one or more subframes within at least one half of each frame transmitted using the initial UL-DL configuration as flexible subframes; and

determining a different UL-DL configuration is to be used for TDD communication with the UE, the different UL-DL configuration comprising at least one flexible subframe in which a transmission direction is to be changed; and

transmitting a reconfiguration message in a first frame indicating that the transmission direction for the at least one flexible subframe is to be changed.

34. The method of claim 33, wherein the reconfiguration message comprises a two-bit message transmitted in the first subframe.

35. The method of claim 34, wherein the transmitting comprises:

transmitting a first reconfiguration message in the first frame indicating that a transmission direction for at least a first flexible subframe is to be changed in the first half of the second frame; and

transmitting a second reconfiguration message in the first frame indicating that a transmission direction for at least a second flexible subframe is to be changed in the second half of the second frame.

36. The method of claim 35, wherein the first reconfiguration message is transmitted in a first subframe of the first frame, and the second reconfiguration message is transmitted in a sixth subframe of the first frame.

37. The method of claim 33, wherein the reconfiguration message is transmitted in a control channel transmission.

38. The method of claim 37, wherein the control channel transmission uses physical control format indicator channel (PCFICH) channel coding to encode the reconfiguration message.

39. The method of claim 33, wherein the reconfiguration message is transmitted in downlink control information (DCI) to the UE.

40. The method of claim 39, wherein the reconfiguration message comprises a two bit message included in DCI format 1, 2, 2A or 2B mapped to a UE specific search space.

41. The method of claim 33, wherein the reconfiguration message is transmitted in a downlink grant to the UE.

42. The method of claim 33, the initial UL-DL configuration is transmitted in a radio resource control (RRC) message to the UE.

43. An apparatus configured to perform time-division duplex (TDD) communications with a user equipment (UE), comprising:

means for determining an initial uplink-downlink (UL-DL) configuration for TDD communication with the UE;

means for determining a different UL-DL configuration is to be used for TDD communication with the UE, the different UL-DL configuration comprising at least one flexible subframe in which a transmission direction is to be changed; and means for transmitting a reconfiguration message in a first frame indicating that the transmission direction for the at least one flexible subframe is to be changed.

44. The apparatus of claim 43, wherein the reconfiguration message comprises a two-bit message transmitted in the first subframe.

45. The apparatus of claim 44, wherein the means for transmitting the reconfiguration message comprises: means for transmitting a first reconfiguration message in the first frame indicating that a transmission direction for at least a first flexible subframe is to be changed in the first half of the second frame; and

means for transmitting a second reconfiguration message in the first frame indicating that a transmission direction for at least a second flexible subframe is to be changed in the second half of the second frame.

46. The apparatus of claim 45, wherein the first reconfiguration message is transmitted in a first subframe of the first frame, and the second reconfiguration message is transmitted in a sixth subframe of the first frame.

47. The apparatus of claim 43, wherein the reconfiguration message is transmitted in a control channel transmission.

48. The apparatus of claim 47, wherein the control channel transmission uses physical control format indicator channel (PCFICH) channel coding to encode the reconfiguration message.

49. The apparatus of claim 43, wherein the reconfiguration message is transmitted in downlink control information (DCI) to the UE.

50. The apparatus of claim 49, wherein the reconfiguration message comprises a two bit message included in DCI format 1, 2, 2A or 2B mapped to a UE specific search space.

51. The apparatus of claim 43, wherein the reconfiguration message is transmitted in a downlink grant to the UE.

52. The apparatus of claim 43, the initial UL-DL configuration is transmitted in a radio resource control (RRC) message to the UE.

53. A base station configured to perform time-division duplex (TDD) communications with a user equipment (UE), comprising:

a processor;

memory in electronic communication with the processor; and instructions stored in the memory, the instructions being executable by the processor to:

determine an initial uplink-downlink (UL-DL) configuration for TDD communication with the UE;

determine a different UL-DL configuration is to be used for TDD communication with the UE, the different UL-DL configuration comprising at least one flexible subframe in which a transmission direction is to be changed; and

transmit a reconfiguration message in a first frame indicating that the transmission direction for the at least one flexible subframe is to be changed.

54. A computer program product for performing time-division duplex (TDD) communications with a user equipment (UE), the computer program product comprising a non-transitory computer-readable medium storing instructions executable by a processor to: