Patent Description:
The background description provided herein is for generally presenting the context of the disclosure. Unless otherwise indicated herein, the materials described in this section are not prior art to the claims in this application and are not admitted to be prior art or suggestions of the prior art, by inclusion in this section.

D2D applications may provide a scalable and universal framework for connecting proximity peers. There are different technology solutions for D2D applications, e.g., based on WiFi Direct or Near Field Communication (NFC) technology. A special solution that relates to the 3rd Generation Partnership Project (3GPP) is Proximity Services (ProSe) as well as Long-Term Evolution (LTE) Direct.

Support of LTE-based D2D discovery and communications is being studied by the 3GPP radio access network (RAN) working groups (WG). In this regard, it was agreed by the RAN1 WG that D2D discovery and communications within network coverage may be supported on the uplink (UL) spectrum in frequency-division duplexing (FDD) systems, and on UL subframes or potentially downlink (DL) subframes as well for time-division duplexing (TDD) systems.

The paper of <NPL>, provides various proposals and observations including aligning symbol timing with UL signal.

The present invention is defined by the features of the independent claims. Preferred advantageous embodiments thereof are defined by the sub-features of the dependent claims.

Embodiments of the present disclosure describe apparatuses and methods for signal designs for device-to-device (D2D) subframes. Various embodiments may include a UE with a radio transceiver to communicate with another UE via D2D communications. The UE may further include processing circuitry to generate a cyclic prefix (CP) with a length greater than <NUM> microseconds for a first or second symbol of a D2D subframe. These and other aspects of the present disclosure will be more fully described below.

In the following detailed description, reference is made to the accompanying drawings, which form a part hereof wherein like numerals designate like parts throughout, and in which is shown by way of illustration embodiments that may be practiced. It is to be understood that other embodiments may be utilized and structural or logical changes may be made without departing from the scope of the present disclosure.

Various operations may be described as multiple discrete actions or operations in turn, in a manner that is most helpful in understanding the claimed subject matter. However, the order of description should not be construed as to imply that these operations are necessarily order dependent. In particular, these operations may not be performed in the order of presentation. Operations described may be performed in a different order than the described embodiment. Various additional operations may be performed and/or described operations may be omitted in additional embodiments.

For the purposes of the present disclosure, the phrase "A, B, and/or C" means (A), (B), (C), (A and B), (A and C), (B and C), or (A, B, and C).

<FIG> schematically illustrates a wireless communication system <NUM> in accordance with various embodiments. The wireless communication system <NUM> may include a backbone network <NUM>, a core/access network <NUM>, and a D2D network <NUM>.

The backbone network <NUM> may be a part of computer network infrastructure that interconnects various sub-networks and provides a path for the exchange of information between these sub-networks. In various embodiments, the backbone network <NUM> may include Internet backbone <NUM>, which may include the principal data routes between large, strategically interconnected computer networks and core routers on the Internet.

The core/access network <NUM> may be connected to the backbone network <NUM>. In various embodiments, the core/access network <NUM> may include one or more radio access networks, such as a Global System for Mobile Communication (GSM), General Packet Radio Service (GPRS), Universal Mobile Telecommunications System (UMTS), High Speed Packet Access (HSPA), Evolved HSPA (E-HSPA), or Long-Term Evolution (LTE) network. In some embodiments, a radio access network may include GSM Enhanced Data rates for GSM Evolution (EDGE) Radio Access Network (GERAN), Universal Terrestrial Radio Access Network (UTRAN), or Evolved UTRAN (E-UTRAN). The core/access network <NUM> may operate in accordance with other network technologies in other embodiments.

Mobile communication technology may rely on various standards and protocols to transmit data between a base station and a wireless communication device. Wireless communication system standards and protocols may include, for example, the 3GPP LTE; the Institute of Electrical and Electronics Engineers (IEEE) <NUM> standard, which is commonly known to industry groups as worldwide interoperability for microwave access (WiMAX); and the IEEE <NUM> standard, which is commonly known as Wi-Fi. In a 3GPP radio access network (RAN), according to LTE, the base station may be referred to as an evolved Node B (also commonly denoted as eNodeB, or eNB). It may communicate with a wireless communication device, known as user equipment (UE). Although the present disclosure is presented with terminology and examples generally directed toward 3GPP systems and standards, the teaching disclosed herein may be applied to any type of wireless network or communication standard.

In various embodiments, the core/access network <NUM> may include eNB <NUM>, NB <NUM>, and mobility management entities (MME) and serving gateways (SGW) <NUM>. eNB <NUM> may be more intelligent than legacy NB <NUM>, which may be used in a <NUM> network such as a UMTS network. For example, radio network controller (RNC) functionality may be located in eNB <NUM> rather than being in a separate RNC entity. In LTE, eNB <NUM> may connect to another eNB, e.g., via an X2 interface, to forward or share information. In some embodiments, the core/access network <NUM> may be an Internet Protocol (IP) based network, wherein interfaces between network entities (e.g., eNB <NUM> and MME/SGW <NUM>) may be based on IP. In some embodiments, MME/SGW <NUM> may communicate with eNB <NUM>, e.g., over an S1 interface. The S1 interface may be similar to the S1 interface as defined in <NPL>) and may support a many-to-many relation between MME/SGW <NUM> and eNB <NUM>. For example, different operators may simultaneously operate the same eNB in a network sharing setting. In some embodiments, communication between the eNB <NUM> and UEs may be facilitated via the MME/SGW <NUM>. The MME/SGW <NUM> may be configured to manage signaling exchanges, e.g., authentication of the UE <NUM>, or perform other actions associated with establishment of a communication link between the UE <NUM> and the core/access network <NUM>. In some embodiments, the MME/SGW <NUM> may be responsible for tracking and paging user equipment, e.g., when the UE <NUM> is in an idle mode.

For ease of illustration, various descriptions herein are provided to conform to 3GPP in the communication system <NUM>; however, the subject matter of the present disclosure is not limited in this regard and the embodiments disclosed herein may be advantageously applied to other wired or wireless communication protocols or networks. For example, in an embodiment in which the core/access network <NUM> includes a UTRAN, the NB <NUM> may take the form of an RNC, which may be configured to communicate with the UEs <NUM>, <NUM>, or <NUM>. In an embodiment where the core/access network <NUM> includes a GERAN, the eNB <NUM> may represent a base station controller (BSC) configured to communicate with the UEs <NUM>, <NUM>, or <NUM> via a base transmission station (BTS).

In various embodiments, the UE <NUM> may access the core/access network <NUM> via a radio link with a base station, e.g., eNB <NUM>. A downlink (DL) transmission may be a communication from the eNB <NUM> to the UE <NUM>. An uplink (UL) transmission may be a communication from the UE <NUM> to the eNB <NUM>. Only limited numbers of UEs and eNBs are illustrated in <FIG> for ease of illustration. However, the communication system <NUM> may include any number of UEs, eNBs, or other servers while practicing suitable embodiments of the present disclosure. As an example, in some embodiments, the core/access network <NUM> may also include other servers, such as a machine type communication (MTC) server (not shown) to facilitate MTC.

In some embodiments, the UE <NUM> may be configured to communicate with another machine using MTC technology. The term MTC, as discussed above, refers to data transmitted to or from user equipment to another machine with little or no human interaction. For example, the UE <NUM> may be a sensor that is electrically coupled to a wireless transceiver (e.g., the transceiver circuitry <NUM>, discussed below with reference to <FIG>), and may be configured to communicate, with little or no intervention, with another machine enabled for MTC. In some embodiments, the wireless transceiver of the UE <NUM> may also be configured to communicate with at least one of a wireless metropolitan area network (WMAN), a wireless local area network (WLAN), or a wireless personal area network (WPAN).

In some embodiments, the UE <NUM> may be a mobile communication device, a subscriber station, or another device that is configured to communicate with the core/access network <NUM>, e.g., via the eNB <NUM>, in conformance with an appropriate protocol (e.g., a multiple-input/multiple-output (MIMO) communication scheme).

In various embodiments, UE <NUM>, UE <NUM>, and UE <NUM> may form a D2D network <NUM>. In the D2D network <NUM>, two UEs in proximity may directly communicate with each other without the assistance of eNB <NUM> or any other base stations and core networks. Direct communication between devices is commonly known as device-to-device (D2D) communication or peer-to-peer (P2P) communication.

As discussed in further detail below, the UEs, <NUM>, <NUM>, and/or <NUM> may be configured for using specially designed subframes for D2D communications. Such subframes may enable the UEs <NUM>, <NUM>, or <NUM> to accommodate the transmit-to-receive or receive-to-transmit (hereinafter, "Tx/Rx") switching time needed in D2D communications. Further, such subframes may enable the UEs <NUM>, <NUM>, or <NUM> to handle the automatic gain control (AGC) setting time in D2D communications.

D2D communication in the D2D network <NUM> may be non-transparent to the core/access network <NUM> and may occur on a cellular spectrum (e.g., inband) or unlicensed spectrum (e.g., outband). D2D communication in the D2D network <NUM> may be realized in different communication technologies. In some embodiments, short-range technologies, such as Bluetooth or Wi-Fi, may be used. In some embodiments, D2D communication may reuse licensed LTE spectrum or unlicensed LTE spectrum.

In various embodiments, D2D communication in the D2D network <NUM> may first include device discovery, whereby UEs are to determine whether they are within range and/or available for D2D communication before establishing a D2D session. Proximity detection may be assisted by the core/access network <NUM>, may be performed at least partially by UEs, or may be performed largely by UEs independently. In various embodiments, D2D discovery may be restricted (also known as closed D2D discovery) or open (also known as promiscuous D2D discovery).

In various embodiments, D2D communication in the D2D network <NUM> may improve spectrum utilization, increase network throughput, reduce transmission delay, offload traffic for eNB <NUM>, and alleviate congestion in the core/access network <NUM>. In this regard, D2D communications may have a wide variety of applications. For example, D2D network <NUM> may be used for local social networks, content sharing, location-based marketing, service advertisements, mobile-to-mobile applications, etc. Enhanced by the teachings in this disclosure, the D2D network <NUM> may become a fallback public safety network that may function even when the core/access network <NUM> becomes unavailable or fails.

Referring now to <FIG>, it is a schematic block diagram illustrating UEs <NUM> and <NUM> in a D2D communication mode in accordance with various embodiments. The UE <NUM> or <NUM> may be similar to, and substantially interchangeable with, UE <NUM>, <NUM>, or <NUM> of <FIG>. In embodiments, the UE <NUM> may include one or more antennas <NUM> and communication module <NUM>. In various embodiments, transceiver circuitry <NUM> and processing circuitry <NUM> within the communication module <NUM> may be coupled with each other as shown. Likewise, the UE <NUM> may include one or more antennas <NUM> and communication module <NUM>. In various embodiments, transceiver circuitry <NUM> and processing circuitry <NUM> within the communication module <NUM> may be coupled with each other as shown.

In the D2D communication mode, UEs <NUM> and <NUM>, whether within network coverage or in partial or outside network coverage, would essentially be operating in a form of TDD mode because D2D devices would transmit and listen on the same carrier subject to half-duplex constraints. Therefore, a challenge rises to accommodate the Tx/Rx switching time of about a length of <NUM> Ts, which is about <NUM> microseconds (µs) as one Ts is <NUM>/(<NUM>*<NUM>) seconds.

Further, UEs <NUM> and <NUM> may need to consider the AGC setting time in the D2D communication mode. The AGC operations in D2D communications are different from those in cellular operations where UEs receive packets only on DL carrier (FDD) or subframes (TDD). In the D2D communications, different UEs may be frequency-multiplexed for different subframes. Further, subframe sets may also depend on the use of different forms of multiple transmission time interval (TTI) transmissions for D2D discovery and communications. Due to the random nature of AGC operations in the D2D communications, UE <NUM> or <NUM> may need different AGC setting times for different subframes.

In various embodiments, the communication module <NUM> may be coupled with the antennas <NUM> to facilitate over-the-air communication of signals between UE <NUM> and UE <NUM> or another UE. For example, the transceiver circuitry <NUM> may be configured to provide various signal processing operations on the signal to the antennas <NUM> with suitable characteristics. In various embodiments, operations of the transceiver circuitry <NUM> may include, but are not limited to, filtering, amplifying, storing, modulating, demodulating, transforming, etc..

The transceiver circuitry <NUM> may be configured to receive signals from the antennas <NUM>, and then transmit the signals to other components of the UE <NUM> and/or for internal processing by the processing circuitry <NUM>. In some embodiments, the processing circuitry <NUM> may generate a guard interval at a subframe for the provision of the Tx/Rx switching time required for D2D communications at a receiving UE. As an example, the processing circuitry <NUM> may generate a cyclic prefix (CP) for the first or second symbol of a D2D subframe at an orthogonal frequency division multiplexing (OFDM) resource block or a single-carrier frequency-division multiple access (SC-FDMA) resource block. In the disclosure herein, such CP may also be referred to as the CP for the first or second OFDM/SC-FDMA symbol, or simply the first or second symbol. In various embodiments, the CP may be long enough (e.g., having a length greater than <NUM>) to accommodate the Tx/Rx switching time required for D2D communications (e.g., about <NUM>).

In various embodiments, the processing circuitry <NUM> may generate a guard interval at the first symbol of a subframe for the provision of the AGC setting time at the receiving UE. In some embodiments, the processing circuitry <NUM> may transmit a reference signal (e.g., uplink demodulation reference signal UTL-DMRS)) in the first OFDMISC-FDMA symbol for the provision of AGC setting time. In some embodiments, the processing circuitry <NUM> may transmit one or more random quadrature phase shift keying (QPSK) symbols in the first OFDM/SC-FDMA symbol for the provision of AGC setting time. In various embodiments, such guard interval may have a length greater than <NUM> microseconds. Therefore, the processing circuitry <NUM> may accommodate the AGC setting time and the Tx/Rx switching time for D2D subframes. In some embodiments, the processing circuitry <NUM> may also use similar techniques to accommodate the AGC setting time and the Tx/Rx switching time at D2D and WAN subframe boundaries, e.g., during the transition between D2D communication and UE-to-eNB communication.

In some embodiments, the UE <NUM> may include one or more antennas <NUM> to concurrently utilize radio resources of multiple respective component carriers. For example, the UE <NUM> may be configured to communicate using orthogonal frequency division multiple access (OFDMA) (in, e.g., downlink communications) and/or single-carrier frequency-division multiple access (SC-FDMA) (in, e.g., uplink communications). In some embodiments, the UE <NUM> may use the transceiver circuitry <NUM> to communicate with another UE via LTE ProSe or LTE Direct. In some embodiments, the UE <NUM> may use the processing circuitry <NUM> to generate subframes that have appropriate guard intervals for both D2D discovery and communication in LTE ProSe or LTE Direct.

In some embodiments, communication module <NUM> may be configured to provide communication services for one or more subscriber identity modules (SIMs) (not shown) with which it is coupled. In some embodiments, the SIMs may be removably coupled with the communication module <NUM>. In other embodiments, the SIMs may be hardware and/or firmware that are permanently coupled with the UE <NUM>. In various embodiments, the SIMs may include full-size SIMs, mini-SIMs, micro-SIMs, nano-SIMs, embedded SIMs, and/or virtual SIMs.

The SIMs may be integrated circuits that securely store subscriber identity information such as international mobile subscriber identity (IMSI) and related keys used to identify and authenticate one or more subscribers using the UE <NUM>. Each SIM may be associated with different subscriber identity information and may or may not be associated with different carriers. In various embodiments, IMSI and related information may be used to facilitate D2D discovery and D2D communications.

Some or all of the transceiver circuitry <NUM> and/or processing circuitry <NUM> may be included in, for example, radio frequency (RF) circuitry or baseband circuitry as described below with respect to <FIG>. In various embodiments, the UE <NUM> or <NUM> may be, may include, or may be included in a single sensor device, a cellular telephone, a personal computer (PC), a notebook, an ultrabook, a netbook, a smartphone, an ultra mobile PC (UMPC), a handheld mobile device, a universal integrated circuit card (UICC), a personal digital assistant (PDA), a Customer Premise Equipment (CPE), a tablet computing device, or other consumer electronics such as MP3 players, digital cameras, and the like. In some embodiments, the UE may include a mobile station, as defined by IEEE <NUM>. 16e (<NUM> or <NUM> (<NUM>) or some other revision of the IEEE <NUM> standard, or user equipment, as defined by 3GPP LTE Release <NUM> (<NUM>), Release <NUM> (<NUM>), Release <NUM> (<NUM>), Release <NUM> (<NUM>), Release <NUM> (under development), or some other revision or release of the 3GPP LTE standards.

<FIG> is a flowchart illustrating a process for generating D2D subframes in accordance with various embodiments. The process <NUM> may be performed by a UE, e.g., the UE <NUM> or <NUM> of <FIG> or any one of the UEs of <FIG>, such as the UE <NUM>, <NUM>, or <NUM>. In various embodiments, the process <NUM> may enable a UE to accommodate the AGC setting time and the Tx/Rx switching time needed between two D2D subframes or in D2D and WAN subframe boundaries.

The process <NUM> may include, at <NUM>, providing a first guard interval at a first symbol of the subframe to facilitate setting up AGC at a receiving UE. In some embodiments, the first guard interval may be set by the processing circuitry <NUM> or <NUM> of <FIG>. In some embodiments, the subframe may be located at an orthogonal frequency division multiplexing (OFDM) resource block or a single-carrier frequency-division multiple access (SC-FDMA) resource block.

A CP for a symbol may be a repetition of the end of the symbol. A CP may serve as a guard interval to help the receiving UE to eliminate the inter-symbol interference from the previous symbol. Further, a CP may facilitate simple frequency-domain processing, such as channel estimation and equalization, since its characteristic of repetition may enable a frequency-selective multipath channel to be modelled as circular convolution. In various embodiments, the receiving UE may discard the CP portion of the symbol. Thus, the CP may be used as a guard interval.

In some embodiments, a CP for the first symbol of the subframe may be generated as the first guard interval. In some embodiments, the CP generated for the first symbol may have a length greater than <NUM> microseconds. In some embodiments, the CP for the second symbol of the subframe may be generated as the first guard interval. The CP in this case may have a length greater than <NUM> microseconds.

The process <NUM> may further include, at <NUM>, providing a second guard interval at the subframe to facilitate Tx/Rx switching at the receiving UE. In some embodiments, the second guard interval may be set by the processing circuitry <NUM> or <NUM> of <FIG>. In some embodiments, at least a part of the last symbol in a subframe may be punctured as the second guard interval to accommodate the Tx/Rx switching time needed at a receiving UE. In some embodiments, at least a part of the first symbol in a subframe may be punctured as the second guard interval to accommodate the Tx/Rx switching time needed at a receiving UE. In some embodiments, at least a part of the last symbol and at least a part of the first symbol may be punctured as the second guard interval to accommodate the Tx/Rx switching time needed at a receiving UE. In various embodiments, the partially or fully punctured portion of the symbol may not be transmitted.

<FIG> is a flowchart illustrating another process for generating D2D subframes in accordance with various embodiments. The process <NUM> may be performed by a UE, e.g., the UE <NUM> or <NUM> of <FIG> or any one of the UEs of <FIG>, such as the UE <NUM>, <NUM>, or <NUM>.

The process <NUM> may include, at <NUM>, generating a CP with a length greater than <NUM> microseconds for the first or second symbol of a D2D subframe to facilitate setting up AGC at the receiving UE. Due to the random nature of AGC operations in the D2D communications, the receiving UE may need different AGC setting times for different subframes. Therefore, the AGC setting time in a subframe may need to be long enough to cover such variations. In various embodiments, such CP may have a length greater than <NUM> microseconds to accommodate the AGC setting time.

In some embodiments, the CP to accommodate the AGC setting time may be generated for the first symbol, e.g., using only the first half of the first symbol as the CP. In some embodiments, the CP to accommodate the AGC setting time may be generated for the second symbol, e.g., using only the second half of the first symbol as the CP or using the whole first symbol as the CP. In the latter case, the CP for the second symbol may have a length greater than <NUM> microseconds. In various embodiments, different CP designs for the first or second symbol may be used to cater different D2D applications.

The process <NUM> may further include, at <NUM>, transmitting a signal in the first symbol of a D2D subframe to facilitate setting up AGC at the receiving UE. In some embodiments, the signal may be a UL-DMRS or an AGC reference signal (RS). In some embodiments, random quadrature phase shift keying (QPSK) symbols may be mapped to the resource elements (REs) of the first symbol. In some embodiments, a normal (about <NUM>) or extended (about <NUM>) CP may be commonly provided for LTE subframes; thus, the useful symbol length may be shorter than the whole symbol length after the regular CP application. In some embodiments, the CP at the first half of a useful symbol length of the first symbol may be generated based on the second half of the useful symbol length of the first symbol. Further, the UL-DMRS may be still kept to the second half of the useful symbol length of the first symbol.

In some embodiments, a new AGC reference signal may also be defined for AGC setting purposes. The AGC RS may use a suitable reference signal sequence with a low peak-to-average-power-ratio (PAPR) common to many transmitting UEs. Further, the AGC RS may be defined on a per-resource block or on a per-resource block set basis. In some embodiments, similar performance may also be realized with the transmission of random QPSK symbols during the first symbol for accommodating the AGC setting time.

The process <NUM> may further include, at <NUM>, puncturing at least a part of the last symbol or the first symbol at the subframe as the second guard interval. In some embodiments, at least a part of the last symbol in a subframe may be punctured as the second guard interval to accommodate the Tx/Rx switching time needed at the receiving UE. In some embodiments, at least a part of the first symbol in a subframe may be punctured as the second guard interval to accommodate the Tx/Rx switching time needed at the receiving UE.

In some embodiments, there is no need to puncture the last or the first symbol if the subframe is to be transmitted ahead of a serving or camping cell downlink (DL) reference time in a time division duplex (TDD) deployment. In some embodiments, a D2D subframe may be transmitted at least <NUM> basic time units ahead of a serving or camping cell downlink reference time in TDD deployments wherein one basic time unit equals <NUM>/<NUM> seconds. The offset of at least <NUM> basic time units may be sufficient to cover the Tx/Rx switching time of about <NUM>. Such full transmission of the last symbol may be applied at least to TDD systems in some cases.

In some embodiments, all D2D UEs, with or without an active timing advance (TA) value, may transmit according to the DL reference time (T1) with an offset (e.g., offset T2 = 624Ts). In other words, UEs may transmit at time T = T1 - T2 when there is no UL WAN subframe immediately following the D2D subframe. Therefore, the overlap between D2D and UL WAN subframes may be avoided. Furthermore, this scheme for D2D transmission in TDD systems may allow better coding gain by not puncturing the last symbol if the D2D subframe is not followed by a UL subframe.

In some embodiments, the last symbol of the D2D subframe may be used as a gap using legacy UL subframe structure, and no special handling of the first symbol of the D2D subframe may be needed. In some embodiments, irrespective of whether the last or first symbol of the D2D subframe are punctured, an increased gap for handling of Tx/Rx switching time may be accommodated by transmitting a D2D subframe at least <NUM> basic time units (e.g., one basic time unit equals <NUM>/<NUM> seconds) ahead of a corresponding reference time of the D2D subframe. As an example, UE <NUM> may receive D2D transmissions from UE <NUM> on subframe n. Subframe n+<NUM> may be a cellular UL subframe on which UE <NUM> is scheduled to transmit UL PUSCH to the serving cell (e.g., when UE <NUM> is in a connected mode with the serving cell). The PUSCH is transmitted following a transmission time given by T = (DL reference time - X), where X = (NTA + NTAoffset) Ts where NTA is the TA command from the eNB, and NTAoffset is <NUM> Ts. If the subframe n is transmitted with the additional <NUM> Ts advancement from UE2, UE <NUM> now may get this additional amount of time-gap (e.g., on top of the last symbol gap in the D2D subframe) to switch from Rx to Tx mode. Thus, UE <NUM> may transmit subframe n+<NUM> with the application of the appropriate timing advance. This may be helpful especially in cases when the NTA value that UE <NUM> needs to apply on subframe n+<NUM> is large, e.g., comparable to one symbol time-duration.

In some embodiments, a UE may be in RRC Connected mode with a serving cell. In some embodiments, a UE may camp on a camping cell in RRC Idle mode, e.g., to perform cell selection, to receive information from the LTE network. Thus, the UE may have the corresponding serving cell downlink reference time in RRC Connected mode, and have the corresponding camping cell downlink reference time in RRC Idle mode.

In various embodiments, a D2D subframe may be transmitted at least <NUM> basic time units ahead of a serving or camping cell downlink reference time in the time division duplex deployment. Thus, with the puncturing of the last symbol of the D2D subframe, the receiving D2D UE may get at least additional <NUM> Ts to switch to Tx mode, and may transmit the next subframe with the appropriate timing advancement.

In some embodiments, a UE may transmit D2D transmissions according to a serving cell uplink reference time (SCURT) in a time division duplex deployment, wherein SCURT = SCDRT - TA, wherein SCDRT refers to the Serving Cell Downlink Reference Time (SCDRT), and TA is the active timing advance value. In this case, the D2D subframe may be transmitted with appropriate timing advancement at a transmission time given by T = SCURT - 624Ts.

<FIG> are schematic diagrams illustrating subframe designs in accordance with various embodiments. <FIG> may illustrate different schematic diagrams for alternative D2D signal structures and their variants to accommodate the AGC setting time and the Tx/Rx switching time needed at a receiving UE. In various embodiments, data symbols may be mapped to the first and/or last symbol. Further, the first and/or last symbol may be punctured, e.g., the transmitting UE may transmit only a part of the OFDM/SC-FDMA symbol to provide guard intervals needed at the receiving UEs. Various different design alternatives incorporating this design principle will be more fully described below.

<FIG> is a schematic diagram illustrating subframe <NUM>. The subframe <NUM> may include two slots, each having a length of about <NUM> milliseconds, and including seven symbols. According to one embodiment, the first half of the first symbol <NUM> or the second half of the last symbol <NUM> may be punctured, thus not to be transmitted. Therefore, the receiving UE may obtain at least <NUM> microseconds of guard interval as the Tx/Rx switching time.

Further, the second half of the first symbol may be used as an effectively longer CP <NUM> for the second data symbol <NUM>. The CP may be generated using the second half of the second data symbol <NUM>. Note that the CP here refers to a new effective CP in addition to the regular CP application, normal or extended, which may already be applied to the first or second symbol. Therefore, subframe <NUM> may provide better protection to the second data symbol <NUM> because the CP length is effectively increased. As a result, the CP may have a length of <NUM>+<NUM> microseconds in a regular LTE CP application, or <NUM>+<NUM> microseconds in an extended LTE CP application. Meanwhile, subframe <NUM> may now provide at least <NUM> microseconds for the receiver to set up AGC.

In various embodiments, subframe <NUM> may be modified to have the entire last symbol punctured out or alternatively to keep the entire last symbol for transmission. The former modification may provide even longer provision for the Tx/Rx switching time. The latter modification of full transmission of the last symbol may be applied at least to TDD systems. In that case, a UE may transmit subframe <NUM> at time T = T1 - T2 when there is no UL WAN subframe immediately following the D2D subframe, wherein T1 is the DL reference time, and T2 is the offset, e.g., 624Ts.

<FIG> is a schematic diagram illustrating subframe <NUM>. The subframe <NUM> may include two slots, each having a length of about <NUM> milliseconds, and including seven symbols. According to one embodiment, the second half of the last symbol <NUM> may be punctured, thus not to be transmitted. Therefore, the receiving UE may obtain at least <NUM> microseconds of guard interval as the Tx/Rx switching time. In other embodiments, the guard time to accommodate the Tx/Rx switching time may be achieved by partial, full, or no puncturing of the last symbol according to the actual application at D2D communications.

Comparing the subframe <NUM> to the subframe <NUM> in <FIG>, there is no puncturing of the first half of the first symbol <NUM> at the subframe <NUM>. Instead, the entire first symbol may be used as a much longer CP for the second data symbol <NUM>. The CP <NUM> may be generated based on the second data symbol <NUM>. In various embodiments, the prolonged CP <NUM> may provide better protection for the second data symbol <NUM> as well as to provide longer time for the receiving UE for setting up AGC.

The subframe <NUM> or <NUM> exploits the first symbol to generate a substantially prolonged effective CP for the second symbol. In various embodiments, the original CP for the second symbol (e.g., <NUM> for normal CP application) may therefore be omitted if the AGC setting time at the receiving UE can be accommodated within <NUM> and <NUM> (without considering the original CP of <NUM> for the first symbol) for subframes <NUM> and <NUM> respectively. Resultantly, the entire length of the second symbol may be utilized to transmit data.

<FIG> is a schematic diagram illustrating subframe <NUM>. The subframe <NUM> may include two slots, each having a length of about <NUM> milliseconds, and including seven symbols. According to one embodiment, the second half of the last symbol <NUM> may be punctured. Therefore, the receiving UE may obtain at least <NUM> microseconds of guard interval as the Tx/Rx switching time.

In other embodiments, the guard time to accommodate the Tx/Rx switching time may be achieved by partial, full, or no puncturing of the last symbol according to a particular D2D application. As an example, the last symbol may not need to be punctured at all if guard time handling is not handled within the D2D discovery or communication region. Instead, the provision for Tx/Rx switching time may be handled via scheduler restrictions for D2D and WAN subframe boundaries.

Compared to the subframe <NUM> or <NUM>, the subframe <NUM> may provide better coding gain that improves packet detection probability. In various embodiments, the first half of the first symbol <NUM> is not punctured. Instead, the first half of the first symbol <NUM> may be used to generate an effective CP <NUM> for the second half <NUM> at the first symbol <NUM>. Consequently, the CP <NUM> may provide at least <NUM> microseconds, in addition to the normal or extended CP applied for D2D subframes, for the receiving UE to set up AGC. As an example, the CP <NUM> may employ a CP length of <NUM> microseconds (e.g., <NUM> of the first half of the first symbol, plus <NUM> of the normal CP provided for the first symbol) to accommodate the AGC setting time. Compared to the subframe <NUM> or <NUM>, the subframe <NUM> does not provide any additional protection to the second symbol, but provides better coding gain.

<FIG> is a schematic diagram illustrating subframe <NUM>. The subframe <NUM> may include two slots, each having a length of about <NUM> milliseconds, and including seven symbols. According to one embodiment, the second half of the last symbol <NUM> may be punctured to provide the receiving UE at least <NUM> microseconds of guard interval as the Tx/Rx switching time.

In various embodiments, a UL-DMRS may be transmitted in the first symbol <NUM> in addition to those UL-DMRS transmitted in the fourth symbol <NUM> and the eleventh symbol <NUM> of the subframe <NUM>. In one embodiment, the base sequence and cyclic shift used for the UL-DMRS on the first symbol <NUM> may be the same as those used for the UL-DMRS on the fourth symbol <NUM> or the eleventh symbol <NUM>.

In some embodiments, depending on the time required for setting up AGC, the first symbol <NUM> may be generated by mapping a regular UL-DMRS to the subcarriers. In this case, the subframe <NUM> may provide about <NUM> microseconds (e.g., <NUM> of the first symbol, plus <NUM> of the normal CP provided for the second symbol) for the AGC setting time at the receiver. In some embodiments, the first half of the first symbol <NUM> may be punctured, instead of or in addition to the last symbol <NUM> being punctured, to provide additional guard period for handling the Tx/Rx switching time. In other embodiments, the puncturing of the first symbol <NUM> may not be necessary if the guard period is accommodated via partial or full puncturing of the last symbol <NUM>.

<FIG> is a schematic diagram illustrating subframe <NUM>. The subframe <NUM> may be similar to the subframe <NUM> in that the second half of the last symbol <NUM> may be punctured to provide the receiving UE at least <NUM> microseconds of guard interval as the Tx/Rx switching time in some embodiments. Also similarly, in various embodiments, a UL-DMRS may be transmitted in the first symbol <NUM> in addition to those UL-DMRS transmitted in the fourth symbol <NUM> and the eleventh symbol <NUM> of the subframe <NUM>.

In some embodiments, the required AGC setting time may be handled within <NUM> microseconds. Therefore, after mapping a UL-DMRS to the first symbol <NUM>, an effective CP <NUM> may be generated at the first half of the first symbol <NUM>, e.g., based on the second half of the first symbol <NUM>, which still contains the partial reference signal <NUM>. The CP in this case may have a length of at least <NUM> microseconds. Such a structure may facilitate better channel estimation and time tracking. For example, the partial reference signal <NUM> in the second half of the first symbol <NUM> may be used to enhance channel estimation, time tracking (e.g., provide more robustness to time offsets between Tx UE and Rx UE by enabling better time tracking), etc. However, the partial reference signal <NUM> at the first symbol <NUM> may not be guaranteed to be usable for channel estimation, time tracking, etc..

In various embodiments, all the subcarriers for the first symbol <NUM> may be loaded as the Physical Uplink Shared Channel (PUSCH) DMRSs. In various embodiments, the first half of the first symbol <NUM> may also be punctured to accommodate the AGC setting time and the Tx/Rx switching time.

<FIG> is a schematic diagram illustrating subframe <NUM>. The subframe <NUM> may be similar to the subframe <NUM> in that the second half of the last symbol <NUM> may be punctured to provide the receiving UE at least <NUM> microseconds of guard interval as the Tx/Rx switching time in some embodiments. Also similarly, UL-DMRS may be transmitted in the fourth symbol <NUM> and the eleventh symbol <NUM> of the subframe <NUM>.

However, the subframe <NUM> may use the first symbol <NUM> to carry an AGC RS rather than the UL-DMRS transmission as in the subframe <NUM>. In some embodiments, the AGC RS may have a low PAPR. In some embodiments, the AGC RS may be defined on a per-resource block (RB) or on a per-resource block sets basis. Any UE transmitting on the same RB may send the same sequence as the AGC RS. The AGC RS may also be the same for all physical resources.

Similar to the subframe <NUM>, the subframe <NUM> may also provide about <NUM> microseconds (e.g., <NUM> of the first symbol, plus <NUM> of the normal CP provided for the second symbol) for the AGC setting time at the receiver. In some embodiments, the first half of the first symbol <NUM> may be punctured, instead of or in addition to the last symbol <NUM> being punctured, to provide additional guard period for handling the Tx/Rx switching time.

Similar to the subframe <NUM>, the subframe <NUM> may generate an effective CP at the first half of the first symbol <NUM>, e.g., based on the second half of the first symbol <NUM>, in some embodiments. However, the AGC RS may not be used to improve the channel estimation and time tracking for the demodulation of the message packet since the AGC RS is common to UEs.

However, the subframe <NUM> may use the first symbol <NUM> to carry random QPSK symbols rather than an AGC RS in the subframe <NUM>. Similarly, the subframe <NUM> may be modified by puncturing the first half of the first symbol <NUM> at the transmitter side if guard period handling (e.g., for Tx/Rx switching time) needs to be applied at the first symbol <NUM>.

Finally, the special handling for the first and/or last symbols, as described in connection with <FIG>, may not be applied to those subframes that occur within multi-TTI transmissions. For instance, if an individual discovery resource comprises one or two physical resource blocks (PRBs) in frequency dimension and two TTIs in time (e.g., for two subframes), then the last symbol of the first TTI and the first symbol of the second TTI may need to be used as regular symbols to realize higher coding gains.

The UE <NUM> or <NUM> as described in connection with <FIG> may be implemented into a system using any suitable hardware, firmware, and/or software configured as desired. <FIG> illustrates, for one embodiment, an example system <NUM> comprising radio frequency (RF) circuitry <NUM>, baseband circuitry <NUM>, application circuitry <NUM>, memory/storage <NUM>, display <NUM>, camera <NUM>, sensor <NUM>, and input/output (I/O) interface <NUM>, coupled with each other at least as shown.

The application circuitry <NUM> may include circuitry such as, but not limited to, one or more single-core or multi-core processors. The processors may be coupled with memory/storage <NUM> and configured to execute instructions stored in the memory/storage <NUM> to enable various applications and/or operating systems running on the system <NUM>.

The processor(s) may include a baseband processor. The baseband circuitry <NUM> may handle various radio control functions that enable communication with one or more radio networks via the RF circuitry <NUM>. The radio control functions may include, but are not limited to, signal modulation, encoding, decoding, radio frequency shifting, etc. In some embodiments, the baseband circuitry <NUM> may provide for communication compatible with one or more radio technologies. For example, in some embodiments, the baseband circuitry <NUM> may support communication with an E-UTRAN and/or other WMAN, a WLAN, or a WPAN.

In various embodiments, baseband circuitry <NUM> may include circuitry to operate with signals that are not strictly considered as being in a baseband frequency. For example, in some embodiments, baseband circuitry <NUM> may include circuitry to operate with signals having an intermediate frequency, which is between a baseband frequency and a radio frequency.

In some embodiments, the processing circuitry <NUM> or <NUM> of <FIG> may be embodied in the application circuitry <NUM> and/or the baseband circuitry <NUM>.

In various embodiments, the RF circuitry <NUM> may include switches, filters, amplifiers, etc., to facilitate the communication with the wireless network.

In various embodiments, RF circuitry <NUM> may include circuitry to operate with signals that are not strictly considered as being in a radio frequency. For example, in some embodiments, RF circuitry <NUM> may include circuitry to operate with signals having an intermediate frequency, which is between a baseband frequency and a radio frequency.

In some embodiments, the transceiver circuitry <NUM> or <NUM> of <FIG> may be embodied in the RF circuitry <NUM>.

In some embodiments, some or all of the constituent components of the baseband circuitry <NUM>, the application circuitry <NUM>, and/or the memory/storage <NUM> may be implemented together on a system on a chip (SOC).

Memory/storage <NUM> may be used to load and store data and/or instructions, for example, for system <NUM>. Memory/storage <NUM> for one embodiment may include any combination of suitable volatile memory (e.g., dynamic random access memory (DRAM)) and/or non-volatile memory (e.g., flash memory).

In various embodiments, the I/O interface <NUM> may include one or more user interfaces to enable user interaction with the system <NUM> and/or peripheral component interfaces to enable peripheral component interaction with the system <NUM>. User interfaces may include, but are not limited to, a physical keyboard or keypad, a touchpad, a speaker, a microphone, etc. Peripheral component interfaces may include, but are not limited to, a non-volatile memory port, a universal serial bus (USB) port, an audio jack, and a power supply interface.

In various embodiments, sensor <NUM> may include one or more sensing devices to determine environmental conditions and/or location information related to the system <NUM>. In some embodiments, the sensors may include, but are not limited to, a gyro sensor, an accelerometer, a proximity sensor, an ambient light sensor, and a positioning unit. The positioning unit may also be part of, or interact with, the baseband circuitry <NUM> and/or RF circuitry <NUM> to communicate with components of a positioning network, e.g., a global positioning system (GPS) satellite.

In various embodiments, the display <NUM> may include a display, e.g., a liquid crystal display, a touch screen display, etc. In some embodiments, the camera <NUM> may include many molded plastic aspheric lens elements made with varying dispersion and refractive indexes. In some embodiments, the camera <NUM> may include two or more lenses to capture three-dimensional images for stereo photography.

In various embodiments, the system <NUM> may be a mobile computing device such as, but not limited to, a laptop computing device, a tablet computing device, a netbook, an ultrabook, a smartphone, etc. In various embodiments, system <NUM> may have more or fewer components, and/or different architectures.

<FIG> illustrates an article of manufacture <NUM> having programming instructions, incorporating aspects of the present disclosure, in accordance with various embodiments. In various embodiments, an article of manufacture may be employed to implement various embodiments of the present disclosure. As shown, the article of manufacture <NUM> may include a computer-readable non-transitory storage medium <NUM> where instructions <NUM> are configured to practice embodiments of or aspects of embodiments of any one of the processes described herein. The storage medium <NUM> may represent a broad range of persistent storage media known in the art, including but not limited to flash memory, dynamic random access memory, static random access memory, an optical disk, a magnetic disk, etc. In embodiments, computer-readable storage medium <NUM> may include one or more computer-readable non-transitory storage media. In other embodiments, computer-readable storage medium <NUM> may be transitory, such as signals, encoded with instructions <NUM>.

Claim 1:
A user equipment, UE, comprising:
one or more antennas; and
communication circuitry, coupled with the one or more antennas, the communication circuitry to communicate, via at least one of the one or more antennas, with another UE (<NUM>, <NUM>) via device-to-device, D2D, communications; and
processing circuitry (<NUM>, <NUM>), coupled to the communications circuitry, the processing circuitry configured to:
generate a cyclic prefix, CP, for a second symbol of a D2D subframe at an orthogonal frequency division multiplexing, OFDM, resource block or a single-carrier frequency-division multiple access, SC-FDMA, resource block, wherein the CP has a length greater than <NUM> microseconds;
use a second half of a useful symbol length of the first symbol, generated using a second half of a useful symbol length of the second symbol, as a part of the CP for the second symbol; and
puncture an entirety of a last symbol of the D2D subframe, or puncture a first half of the useful symbol length of the first symbol and a second half of a useful symbol length of the last symbol.
wherein the communication circuitry is further to transmit the D2D subframe to the other UE.