PATENT DOCUMENT

Publication Number: US-11140710-B2
Application Number: US-201916408378-A
Country: US
Kind Code: B2

Title: Signal designs for D2D subframes

Abstract:
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) for a 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. Other embodiments may be described and/or claimed.

Claims:
What is claimed is: 
     
       1. A user equipment (UE), comprising:
 one or more antennas; and 
 communication circuitry, coupled with the one or more antennas, the communication circuitry to transmit, via at least one of the one or more antennas, a device-to-device (D2D) subframe to another UE at a Timing (T) ahead of a downlink reference time (T 1 ) with a Timing Advance (TA), where T=(T 1 −TA) and the downlink reference time is associated with a serving cell provided by a base station with which the UE is communicatively coupled, and 
 wherein the D2D subframe does not include a last data symbol of the subframe. 
 
     
     
       2. The UE of  claim 1 , wherein the Timing Advance (TA) is at least 624 basic time units, where one basic time unit equals to 1/30720000 seconds. 
     
     
       3. The UE of  claim 1 , wherein the communication circuitry is to communicate with the other UE via a time division duplex (TDD) deployment. 
     
     
       4. The UE of  claim 1 , wherein the last data symbol not transmitted by the communication circuitry is a Single Carrier Frequency-Division Multiple Access (SC-FDMA) symbol. 
     
     
       5. The UE of  claim 1 , wherein the communication circuitry is to communicate with the other UE via D2D communication without involvement of the base station. 
     
     
       6. The UE of  claim 1 , wherein the communication circuitry is to receive a first value from the base station, and
 wherein a processing circuitry included in the UE is to determine the Timing Advance (TA) based on the first value. 
 
     
     
       7. The UE of  claim 1 , wherein the Timing Advance (TA) equals (N_TA+624)*basic time units (Ts), and
 wherein the N_TA is predetermined by the base station. 
 
     
     
       8. The UE of  claim 7 , wherein the UE is to schedule a switch from reception to transmission within a time period of the TA. 
     
     
       9. A user equipment (UE), comprising:
 one or more antennas; and 
 communication circuitry, coupled with the one or more antennas, the communication circuitry to receive, via at least one of the one or more antennas, a device-to-device (D2D) subframe from another UE at a Timing (T) ahead of a downlink reference time (T 1 ) with a Timing Advance (TA), where T=(T 1 −TA) and the downlink reference time is associated with a serving cell provided by a base station with which the UE is communicatively coupled, and 
 wherein the D2D subframe does not include a last data symbol of the subframe. 
 
     
     
       10. The UE of  claim 9 , wherein the Timing Advance (TA) is at least 624 basic time units, where one basic time unit equals to 1/30720000 seconds. 
     
     
       11. The UE of  claim 9 , wherein the communication circuitry is to communicate with the other UE via a time division duplex (TDD) deployment. 
     
     
       12. The UE of  claim 9 , wherein the last data symbol is a Single Carrier Frequency-Division Multiple Access (SC-FDMA) symbol. 
     
     
       13. The UE of  claim 9 , wherein the communication circuitry is to communicate with the other UE via D2D communication without involvement of the base station. 
     
     
       14. The UE of  claim 9 , wherein the Timing Advance (TA) equals (N_TA+624)*basic time units (Ts), and
 wherein the N_TA is predetermined by the base station. 
 
     
     
       15. The UE of  claim 9 , wherein the UE is to schedule a switch from reception to transmission within a time period of the TA. 
     
     
       16. A processor for a user equipment (UE), the processor comprising:
 circuitry configured to execute one or more instructions to perform operations comprising:
 communicating, via one or more antennas of the UE, a device-to-device (D2D) subframe from another UE at a Timing (T) ahead of a downlink reference time (T 1 ) with a Timing Advance (TA), where T=(T 1 −TA) and the downlink reference time is associated with a serving cell provided by a base station with which the UE is communicatively coupled, and 
 wherein the D2D subframe does not include a last data symbol of the subframe. 
 
 
     
     
       17. The processor of  claim 16 , wherein the Timing Advance (TA) is at least 624 basic time units, where one basic time unit equals to 1/30720000 seconds. 
     
     
       18. The processor of  claim 16 , wherein the circuitry is to communicate with the other UE via a time division duplex (TDD) deployment, and
 wherein the last data symbol is a Single Carrier Frequency-Division Multiple Access (SC-FDMA) symbol. 
 
     
     
       19. The processor of  claim 16 , wherein the Timing Advance (TA) equals (N_TA+624)*basic time units (Ts), and
 wherein the N_TA is predetermined by the base station. 
 
     
     
       20. The processor of  claim 16 , wherein the processor is to schedule a switch from reception to transmission within a time period of the TA.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     This application is a continuation of U.S. patent application Ser. No. 15/492,844, filed Apr. 20, 2017, entitled “SIGNAL DESIGNS FOR D2D SUBFRAMES,” which is a continuation of U.S. patent application Ser. No. 14/498,276, filed Sep. 26, 2014, entitled “SIGNAL DESIGNS FOR D2D SUBFRAMES,” which claims priority to U.S. Provisional Patent Application No. 61/909,938, filed Nov. 27, 2013, entitled “ADVANCED WIRELESS COMMUNICATION SYSTEMS AND TECHNIQUES,” disclosures of which are hereby incorporated by reference in their entireties. 
    
    
     FIELD 
     Embodiments of the present disclosure generally relate to the field of wireless communication, and more particularly, to apparatuses and methods for signal designs for device-to-device (D2D) subframes. 
     BACKGROUND 
     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. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Embodiments will be readily understood by the following detailed description in conjunction with the accompanying drawings. To facilitate this description, like reference numerals designate like structural elements. Embodiments are illustrated by way of example and not by way of limitation in the figures of the accompanying drawings. 
         FIG. 1  schematically illustrates a wireless communication system in accordance with various embodiments. 
         FIG. 2  is a schematic block diagram illustrating two user equipment (UE) devices in a D2D communication mode in accordance with various embodiments. 
         FIG. 3  is a flowchart illustrating a process for generating D2D subframes in accordance with various embodiments. 
         FIG. 4  is a flowchart illustrating another process for generating D2D subframes in accordance with various embodiments. 
         FIGS. 5-11  are schematic diagrams illustrating subframe designs in accordance with various embodiments. 
         FIG. 12  is a block diagram of an example computing device that may be used to practice various embodiments described herein. 
         FIG. 13  illustrates an article of manufacture having programming instructions, incorporating aspects of the present disclosure, in accordance with various embodiments. 
     
    
    
     DETAILED DESCRIPTION 
     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 33.33 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 and/or B” means (A), (B), or (A and B). 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). The description may use the phrases “in an embodiment,” or “in embodiments,” which may each refer to one or more of the same or different embodiments. Furthermore, the terms “comprising,” “including,” “having,” and the like, as used with respect to embodiments of the present disclosure, are synonymous. 
     As used herein, the term “circuitry” may refer to, be part of, or include an Application Specific Integrated Circuit (ASIC), an electronic circuit, a processor (shared, dedicated, or group), and/or memory (shared, dedicated, or group) that execute one or more software or firmware programs, a combinational logic circuit, and/or other suitable hardware components that provide the described functionality. 
       FIG. 1  schematically illustrates a wireless communication system  100  in accordance with various embodiments. The wireless communication system  100  may include a backbone network  110 , a core/access network  120 , and a D2D network  130 . 
     The backbone network  110  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  110  may include Internet backbone  112 , which may include the principal data routes between large, strategically interconnected computer networks and core routers on the Internet. 
     The core/access network  120  may be connected to the backbone network  110 . In various embodiments, the core/access network  120  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  120  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) 802.16 standard, which is commonly known to industry groups as worldwide interoperability for microwave access (WiMAX); and the IEEE 802.11 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  120  may include eNB  124 , NB  126 , and mobility management entities (MME) and serving gateways (SGW)  122 . eNB  124  may be more intelligent than legacy NB  126 , which may be used in a 3G network such as a UMTS network. For example, radio network controller (RNC) functionality may be located in eNB  124  rather than being in a separate RNC entity. In LTE, eNB  124  may connect to another eNB, e.g., via an X2 interface, to forward or share information. In some embodiments, the core/access network  120  may be an Internet Protocol (IP) based network, wherein interfaces between network entities (e.g., eNB  124  and MME/SGW  122 ) may be based on IP. In some embodiments, MME/SGW  122  may communicate with eNB  124 , e.g., over an S1 interface. The S1 interface may be similar to the S1 interface as defined in 3GPP TS 36.410 V11.1.0 (2013-09) and may support a many-to-many relation between MME/SGW  122  and eNB  124 . For example, different operators may simultaneously operate the same eNB in a network sharing setting. In some embodiments, communication between the eNB  124  and UEs may be facilitated via the MME/SGW  122 . The MME/SGW  122  may be configured to manage signaling exchanges, e.g., authentication of the UE  132 , or perform other actions associated with establishment of a communication link between the UE  132  and the core/access network  120 . In some embodiments, the MME/SGW  122  may be responsible for tracking and paging user equipment, e.g., when the UE  132  is in an idle mode. 
     For ease of illustration, various descriptions herein are provided to conform to 3GPP in the communication system  100 ; 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  120  includes a UTRAN, the NB  126  may take the form of an RNC, which may be configured to communicate with the UEs  132 ,  134 , or  136 . In an embodiment where the core/access network  120  includes a GERAN, the eNB  124  may represent a base station controller (BSC) configured to communicate with the UEs  132 ,  134 , or  136  via a base transmission station (BTS). 
     In various embodiments, the UE  132  may access the core/access network  120  via a radio link with a base station, e.g., eNB  124 . A downlink (DL) transmission may be a communication from the eNB  124  to the UE  132 . An uplink (UL) transmission may be a communication from the UE  132  to the eNB  124 . Only limited numbers of UEs and eNBs are illustrated in  FIG. 1  for ease of illustration. However, the communication system  100  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  120  may also include other servers, such as a machine type communication (MTC) server (not shown) to facilitate MTC. 
     In some embodiments, the UE  134  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  134  may be a sensor that is electrically coupled to a wireless transceiver (e.g., the transceiver circuitry  224 , discussed below with reference to  FIG. 2 ), 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  134  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  136  may be a mobile communication device, a subscriber station, or another device that is configured to communicate with the core/access network  120 , e.g., via the eNB  124 , in conformance with an appropriate protocol (e.g., a multiple-input/multiple-output (MIMO) communication scheme). 
     In various embodiments, UE  132 , UE  134 , and UE  136  may form a D2D network  130 . In the D2D network  130 , two UEs in proximity may directly communicate with each other without the assistance of eNB  124  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,  132 ,  134 , and/or  136  may be configured for using specially designed subframes for D2D communications. Such subframes may enable the UEs  132 ,  134 , or  136  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  132 ,  134 , or  136  to handle the automatic gain control (AGC) setting time in D2D communications. 
     D2D communication in the D2D network  130  may be non-transparent to the core/access network  120  and may occur on a cellular spectrum (e.g., inband) or unlicensed spectrum (e.g., outband). D2D communication in the D2D network  130  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  130  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  120 , 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  130  may improve spectrum utilization, increase network throughput, reduce transmission delay, offload traffic for eNB  124 , and alleviate congestion in the core/access network  120 . In this regard, D2D communications may have a wide variety of applications. For example, D2D network  130  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  130  may become a fallback public safety network that may function even when the core/access network  120  becomes unavailable or fails. 
     Referring now to  FIG. 2 , it is a schematic block diagram illustrating UEs  210  and  220  in a D2D communication mode in accordance with various embodiments. The UE  210  or  220  may be similar to, and substantially interchangeable with, UE  132 ,  134 , or  136  of  FIG. 1 . In embodiments, the UE  210  may include one or more antennas  218  and communication module  212 . In various embodiments, transceiver circuitry  214  and processing circuitry  216  within the communication module  212  may be coupled with each other as shown. Likewise, the UE  220  may include one or more antennas  228  and communication module  222 . In various embodiments, transceiver circuitry  224  and processing circuitry  226  within the communication module  222  may be coupled with each other as shown. 
     In the D2D communication mode, UEs  210  and  220 , 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 624 T s , which is about 20.3 microseconds (μs) as one T s  is 1/(15000*2048) seconds. 
     Further, UEs  210  and  220  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  210  or  220  may need different AGC setting times for different subframes. 
     In various embodiments, the communication module  222  may be coupled with the antennas  228  to facilitate over-the-air communication of signals between UE  220  and UE  210  or another UE. For example, the transceiver circuitry  224  may be configured to provide various signal processing operations on the signal to the antennas  228  with suitable characteristics. In various embodiments, operations of the transceiver circuitry  224  may include, but are not limited to, filtering, amplifying, storing, modulating, demodulating, transforming, etc. 
     The transceiver circuitry  224  may be configured to receive signals from the antennas  228 , and then transmit the signals to other components of the UE  220  and/or for internal processing by the processing circuitry  226 . In some embodiments, the processing circuitry  226  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  226  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 33.33 μs) to accommodate the Tx/Rx switching time required for D2D communications (e.g., about 20.3 μs). 
     In various embodiments, the processing circuitry  226  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  226  may transmit a reference signal (e.g., uplink demodulation reference signal (UL-DMRS)) in the first OFDM/SC-FDMA symbol for the provision of AGC setting time. In some embodiments, the processing circuitry  226  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 33.33 microseconds. Therefore, the processing circuitry  226  may accommodate the AGC setting time and the Tx/Rx switching time for D2D subframes. In some embodiments, the processing circuitry  226  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  220  may include one or more antennas  228  to concurrently utilize radio resources of multiple respective component carriers. For example, the UE  220  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  220  may use the transceiver circuitry  224  to communicate with another UE via LTE ProSe or LTE Direct. In some embodiments, the UE  220  may use the processing circuitry  226  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  222  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  222 . In other embodiments, the SIMs may be hardware and/or firmware that are permanently coupled with the UE  220 . 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  220 . 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  224  and/or processing circuitry  226  may be included in, for example, radio frequency (RF) circuitry or baseband circuitry as described below with respect to  FIG. 12 . In various embodiments, the UE  220  or  210  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 802.16e (2005 or 802.16m (2009) or some other revision of the IEEE 802.16 standard, or user equipment, as defined by 3GPP LTE Release 8 (2008), Release 9 (2009), Release 10 (2011), Release 12 (2014), Release 13 (under development), or some other revision or release of the 3GPP LTE standards. 
       FIG. 3  is a flowchart illustrating a process for generating D2D subframes in accordance with various embodiments. The process  300  may be performed by a UE, e.g., the UE  210  or  220  of  FIG. 2  or any one of the UEs of  FIG. 1 , such as the UE  132 ,  134 , or  136 . In various embodiments, the process  300  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  300  may include, at  310 , 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  216  or  226  of  FIG. 2 . 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 33.33 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 66.67 microseconds. 
     The process  300  may further include, at  320 , 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  216  or  226  of  FIG. 2 . 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. 4  is a flowchart illustrating another process for generating D2D subframes in accordance with various embodiments. The process  400  may be performed by a UE, e.g., the UE  210  or  220  of  FIG. 2  or any one of the UEs of  FIG. 1 , such as the UE  132 ,  134 , or  136 . 
     The process  400  may include, at  410 , generating a CP with a length greater than 33.33 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 33.33 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 66.67 microseconds. In various embodiments, different CP designs for the first or second symbol may be used to cater different D2D applications. 
     The process  400  may further include, at  420 , 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 4.7 μs) or extended (about 16.7 μs) 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  400  may further include, at  430 , 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 624 basic time units ahead of a serving or camping cell downlink reference time in TDD deployments wherein one basic time unit equals 1/30720000 seconds. The offset of at least 624 basic time units may be sufficient to cover the Tx/Rx switching time of about 20.3 μs. 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 (T 1 ) with an offset (e.g., offset T 2 =624 Ts). In other words, UEs may transmit at time T=T 1 −T 2  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 624 basic time units (e.g., one basic time unit equals 1/30720000 seconds) ahead of a corresponding reference time of the D2D subframe. As an example, UE  1  may receive D2D transmissions from UE  2  on subframe n. Subframe n+1 may be a cellular UL subframe on which UE  1  is scheduled to transmit UL PUSCH to the serving cell (e.g., when UE  1  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=(N TA +N TAoffset ) T s  where N TA  is the TA command from the eNB, and N TAoffset  is 624 T s . If the subframe n is transmitted with the additional 624 T s  advancement from UE 2 , UE  1  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  1  may transmit subframe n+1 with the application of the appropriate timing advance. This may be helpful especially in cases when the N TA  value that UE  1  needs to apply on subframe n+1 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 624 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 624 T s  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 (SCDRT) in a time division duplex deployment, wherein SCDRT=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−624 T s . 
       FIGS. 5-11  are schematic diagrams illustrating subframe designs in accordance with various embodiments.  FIGS. 5-11  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. 5  is a schematic diagram illustrating subframe  500 . The subframe  500  may include two slots, each having a length of about 0.5 milliseconds, and including seven symbols. According to one embodiment, the first half of the first symbol  510  or the second half of the last symbol  520  may be punctured, thus not to be transmitted. Therefore, the receiving UE may obtain at least 66.67 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  530  for the second data symbol  540 . The CP may be generated using the second half of the second data symbol  540 . 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  500  may provide better protection to the second data symbol  540  because the CP length is effectively increased. As a result, the CP may have a length of 33.33+4.7 microseconds in a regular LTE CP application, or 33.33+16.7 microseconds in an extended LTE CP application. Meanwhile, subframe  500  may now provide at least 33.33 microseconds for the receiver to set up AGC. 
     In various embodiments, subframe  500  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  500  at time T=T 1 −T 2  when there is no UL WAN subframe immediately following the D2D subframe, wherein T 1  is the DL reference time, and T 2  is the offset, e.g., 624 Ts. 
       FIG. 6  is a schematic diagram illustrating subframe  600 . The subframe  600  may include two slots, each having a length of about 0.5 milliseconds, and including seven symbols. According to one embodiment, the second half of the last symbol  620  may be punctured, thus not to be transmitted. Therefore, the receiving UE may obtain at least 33.33 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  600  to the subframe  500  in  FIG. 5 , there is no puncturing of the first half of the first symbol  610  at the subframe  600 . Instead, the entire first symbol may be used as a much longer CP for the second data symbol  640 . The CP  630  may be generated based on the second data symbol  640 . In various embodiments, the prolonged CP  630  may provide better protection for the second data symbol  640  as well as to provide longer time for the receiving UE for setting up AGC. 
     The subframe  500  or  600  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., 4.7 μs for normal CP application) may therefore be omitted if the AGC setting time at the receiving UE can be accommodated within 33.33 μs and 66.67 μs (without considering the original CP of 4.7 μs for the first symbol) for subframes  500  and  600  respectively. Resultantly, the entire length of the second symbol may be utilized to transmit data. 
       FIG. 7  is a schematic diagram illustrating subframe  700 . The subframe  700  may include two slots, each having a length of about 0.5 milliseconds, and including seven symbols. According to one embodiment, the second half of the last symbol  720  may be punctured. Therefore, the receiving UE may obtain at least 33.33 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  500  or  600 , the subframe  700  may provide better coding gain that improves packet detection probability. In various embodiments, the first half of the first symbol  710  is not punctured. Instead, the first half of the first symbol  710  may be used to generate an effective CP  730  for the second half  740  at the first symbol  710 . Consequently, the CP  730  may provide at least 33.33 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  730  may employ a CP length of 38.03 microseconds (e.g., 33.33 μs of the first half of the first symbol, plus 4.7 μs of the normal CP provided for the first symbol) to accommodate the AGC setting time. Compared to the subframe  500  or  600 , the subframe  700  does not provide any additional protection to the second symbol, but provides better coding gain. 
       FIG. 8  is a schematic diagram illustrating subframe  800 . The subframe  800  may include two slots, each having a length of about 0.5 milliseconds, and including seven symbols. According to one embodiment, the second half of the last symbol  820  may be punctured to provide the receiving UE at least 33.33 microseconds of guard interval as the Tx/Rx switching time. 
     In various embodiments, a UL-DMRS may be transmitted in the first symbol  810  in addition to those UL-DMRS transmitted in the fourth symbol  830  and the eleventh symbol  840  of the subframe  800 . In one embodiment, the base sequence and cyclic shift used for the UL-DMRS on the first symbol  810  may be the same as those used for the UL-DMRS on the fourth symbol  830  or the eleventh symbol  840 . 
     In some embodiments, depending on the time required for setting up AGC, the first symbol  810  may be generated by mapping a regular UL-DMRS to the subcarriers. In this case, the subframe  800  may provide about 71.37 microseconds (e.g., 66.67 μs of the first symbol, plus 4.7 μs 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  810  may be punctured, instead of or in addition to the last symbol  820  being punctured, to provide additional guard period for handling the Tx/Rx switching time. In other embodiments, the puncturing of the first symbol  810  may not be necessary if the guard period is accommodated via partial or full puncturing of the last symbol  820 . 
       FIG. 9  is a schematic diagram illustrating subframe  900 . The subframe  900  may be similar to the subframe  800  in that the second half of the last symbol  920  may be punctured to provide the receiving UE at least 33.33 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  910  in addition to those UL-DMRS transmitted in the fourth symbol  930  and the eleventh symbol  940  of the subframe  900 . 
     In some embodiments, the required AGC setting time may be handled within 33.33 microseconds. Therefore, after mapping a UL-DMRS to the first symbol  910 , an effective CP  950  may be generated at the first half of the first symbol  910 , e.g., based on the second half of the first symbol  910 , which still contains the partial reference signal  960 . The CP in this case may have a length of at least 33.33 microseconds. Such a structure may facilitate better channel estimation and time tracking. For example, the partial reference signal  960  in the second half of the first symbol  910  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  960  at the first symbol  910  may not be guaranteed to be usable for channel estimation, time tracking, etc. 
     In various embodiments, all the subcarriers for the first symbol  910  may be loaded as the Physical Uplink Shared Channel (PUSCH) DMRSs. In various embodiments, the first half of the first symbol  910  may also be punctured to accommodate the AGC setting time and the Tx/Rx switching time. 
       FIG. 10  is a schematic diagram illustrating subframe  1000 . The subframe  1000  may be similar to the subframe  800  in that the second half of the last symbol  1020  may be punctured to provide the receiving UE at least 33.33 microseconds of guard interval as the Tx/Rx switching time in some embodiments. Also similarly, UL-DMRS may be transmitted in the fourth symbol  1030  and the eleventh symbol  1040  of the subframe  1000 . 
     However, the subframe  1000  may use the first symbol  1010  to carry an AGC RS rather than the UL-DMRS transmission as in the subframe  800 . 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  800 , the subframe  1000  may also provide about 71.37 microseconds (e.g., 66.67 μs of the first symbol, plus 4.7 μs 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  1010  may be punctured, instead of or in addition to the last symbol  1020  being punctured, to provide additional guard period for handling the Tx/Rx switching time. 
     Similar to the subframe  900 , the subframe  1000  may generate an effective CP at the first half of the first symbol  1010 , e.g., based on the second half of the first symbol  1010 , 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. 
       FIG. 11  is a schematic diagram illustrating subframe  1100 . The subframe  1100  may be similar to the subframe  1000  in that the second half of the last symbol  1120  may be punctured to provide the receiving UE at least 33.33 microseconds of guard interval as the Tx/Rx switching time in some embodiments. Also similarly, UL-DMRS may be transmitted in the fourth symbol  1130  and the eleventh symbol  1140  of the subframe  1100 . 
     However, the subframe  1100  may use the first symbol  1110  to carry random QPSK symbols rather than an AGC RS in the subframe  1000 . Similarly, the subframe  1100  may be modified by puncturing the first half of the first symbol  1110  at the transmitter side if guard period handling (e.g., for Tx/Rx switching time) needs to be applied at the first symbol  1110 . 
     Finally, the special handling for the first and/or last symbols, as described in connection with  FIGS. 8-11 , 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  210  or  220  as described in connection with  FIG. 2  may be implemented into a system using any suitable hardware, firmware, and/or software configured as desired.  FIG. 12  illustrates, for one embodiment, an example system  1200  comprising radio frequency (RF) circuitry  1210 , baseband circuitry  1220 , application circuitry  1230 , memory/storage  1240 , display  1250 , camera  1260 , sensor  1270 , and input/output (I/O) interface  1280 , coupled with each other at least as shown. 
     The application circuitry  1230  may include circuitry such as, but not limited to, one or more single-core or multi-core processors. The processor(s) may include any combination of general-purpose processors and dedicated processors (e.g., graphics processors, application processors, etc.). The processors may be coupled with memory/storage  1240  and configured to execute instructions stored in the memory/storage  1240  to enable various applications and/or operating systems running on the system  1200 . 
     The baseband circuitry  1220  may include circuitry such as, but not limited to, one or more single-core or multi-core processors. The processor(s) may include a baseband processor. The baseband circuitry  1220  may handle various radio control functions that enable communication with one or more radio networks via the RF circuitry  1210 . 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  1220  may provide for communication compatible with one or more radio technologies. For example, in some embodiments, the baseband circuitry  1220  may support communication with an E-UTRAN and/or other WMAN, a WLAN, or a WPAN. Embodiments in which the baseband circuitry  1220  is configured to support radio communications of more than one wireless protocol may be referred to as multi-mode baseband circuitry. 
     In various embodiments, baseband circuitry  1220  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  1220  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  216  or  226  of  FIG. 2  may be embodied in the application circuitry  1230  and/or the baseband circuitry  1220 . 
     RF circuitry  1210  may enable communication with wireless networks using modulated electromagnetic radiation through a non-solid medium. In various embodiments, the RF circuitry  1210  may include switches, filters, amplifiers, etc., to facilitate the communication with the wireless network. 
     In various embodiments, RF circuitry  1210  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  1210  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  214  or  224  of  FIG. 2  may be embodied in the RF circuitry  1210 . 
     In some embodiments, some or all of the constituent components of the baseband circuitry  1220 , the application circuitry  1230 , and/or the memory/storage  1240  may be implemented together on a system on a chip (SOC). 
     Memory/storage  1240  may be used to load and store data and/or instructions, for example, for system  1200 . Memory/storage  1240  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  1280  may include one or more user interfaces to enable user interaction with the system  1200  and/or peripheral component interfaces to enable peripheral component interaction with the system  1200 . 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  1270  may include one or more sensing devices to determine environmental conditions and/or location information related to the system  1200 . 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  1220  and/or RF circuitry  1210  to communicate with components of a positioning network, e.g., a global positioning system (GPS) satellite. 
     In various embodiments, the display  1250  may include a display, e.g., a liquid crystal display, a touch screen display, etc. In some embodiments, the camera  1260  may include many molded plastic aspheric lens elements made with varying dispersion and refractive indexes. In some embodiments, the camera  1260  may include two or more lenses to capture three-dimensional images for stereo photography. 
     In various embodiments, the system  1200  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  1200  may have more or fewer components, and/or different architectures. 
       FIG. 13  illustrates an article of manufacture  1310  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  1310  may include a computer-readable non-transitory storage medium  1320  where instructions  1330  are configured to practice embodiments of or aspects of embodiments of any one of the processes described herein. The storage medium  1320  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  1320  may include one or more computer-readable non-transitory storage media. In other embodiments, computer-readable storage medium  1320  may be transitory, such as signals, encoded with instructions  1330 . 
     In various embodiments, instructions  1330  may enable an apparatus, in response to its execution by the apparatus, to perform various operations described herein. As an example, storage medium  1320  may include instructions  1330  configured to cause an apparatus, e.g., UE  210  in connection with  FIG. 2 , to practice some aspects of provisioning of guard intervals in a subframe, e.g., as illustrated in process  300  of  FIG. 3 , in accordance with embodiments of the present disclosure. As another example, storage medium  1320  may include instructions  1330  configured to cause an apparatus, e.g., UE  220  in connection with  FIG. 2 , to practice some aspects of provisioning of guard intervals in a subframe, e.g., as illustrated in process  400  of  FIG. 4 , in accordance with embodiments of the present disclosure. 
     The following paragraphs describe examples of various embodiments. 
     Example 1 is a user equipment (UE) including a radio transceiver to communicate with another UE via device-to-device (D2D) communications. The UE may further include processing circuitry, coupled to the radio transceiver, to generate a cyclic prefix (CP) for a 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, wherein the CP has a length greater than 33.33 microseconds. 
     Example 2 includes the subject matter of example 1, wherein the processing circuitry is further to puncture a first half of a useful symbol length of the first symbol and/or a second half of a useful symbol length of a last symbol of the D2D subframe. 
     Example 3 includes the subject matter of example 1 or 2, wherein the processing circuitry does not puncture a last symbol of the D2D subframe unless the D2D subframe is followed by an uplink subframe. 
     Example 4 includes the subject matter of any one of examples 1-3, wherein the processing circuitry is to use a second half of a useful symbol length of the first symbol, generated based on a second half of a useful symbol length of the second symbol, as a part of the CP for the second symbol. 
     Example 5 includes the subject matter of example 4, wherein the processing circuitry is further to puncture an entirety of a last symbol of the D2D subframe, or to 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. 
     Example 6 includes the subject matter of any one of examples 1-5, wherein the processing circuitry is to use a first half of a useful symbol length of the first symbol, generated based on a second half of the useful symbol length of the first symbol, as a part of the CP for the first symbol. 
     Example 7 includes the subject matter of any one of examples 1-6, wherein the processing circuitry is to generate the CP having a length greater than 66.67 microseconds for the second symbol. 
     Example 8 is a user equipment (UE) including a radio transceiver to communicate with another UE via Long-Term Evolution (LTE) Proximity Services (ProSe) or LTE Direct. The UE may further include processing circuitry, coupled to the radio transceiver, to transmit a signal in a first symbol of a D2D subframe at an OFDM resource block or an SC-FDMA resource block, for AGC setting at a receiving UE. 
     Example 9 includes the subject matter of example 8, wherein the processing circuitry is further to generate a cyclic prefix to be greater than 66.67 microseconds for a second symbol of the D2D subframe. 
     Example 10 includes the subject matter of example 8 or 9, wherein the processing circuitry is to use a UL-DMRS as the signal in the first symbol, and wherein a base sequence and a cyclic shift of the UL-DMRS are the same as those used for respective UL-DMRS on a fourth symbol and an eleventh symbol of the subframe. 
     Example 11 includes the subject matter of example 10, wherein the processing circuitry is to use a first half of a useful symbol length of the first symbol, generated based on a second half of the useful symbol length of the first symbol, as a part of an cyclic prefix for the first symbol; and to keep the UL-DMRS at a second half of the useful symbol length of the first symbol. 
     Example 12 includes the subject matter of example 10, wherein the processing circuitry is to map the UL-DMRS to an entirety of a non-cyclic-prefix portion of the first symbol. 
     Example 13 includes the subject matter of example 8 or 9, wherein the processing circuitry is to use an AGC reference signal as the signal, wherein the AGC reference signal is a sequence that has a peak-to-average-power-ratio (PAPR) and is common to a plurality of transmitting UEs, and wherein the AGC reference signal is defined on a per-resource block or on a per-resource block set basis. 
     Example 14 includes the subject matter of example 8 or 9, wherein the processing circuitry is to transmit random Quadrature Phase Shift Keying (QPSK) symbols on the first symbol as the signal. 
     Example 15 includes the subject matter of any one of examples 8-14, wherein the processing circuitry is to puncture a first half of a useful symbol length of the first symbol. 
     Example 16 is a method for signal designs for D2D subframes. The method may include providing a first guard interval at a first symbol of a subframe to facilitate setting up AGC at a receiving UE; and providing a second guard interval at the subframe to facilitate transmit-to-receive or receive-to-transmit switching at the receiving UE. 
     Example 17 includes the subject matter of example 16, and further includes generating a CP for the first symbol of the subframe as the first guard interval, wherein the CP has a length greater than 33.33 microseconds. 
     Example 18 includes the subject matter of example 16, and further includes generating a CP for a second symbol of the subframe as the first guard interval, wherein the CP has a length greater than 66.67 microseconds. 
     Example 19 includes the subject matter of any one of examples 16-18, and further includes mapping random quadrature phase shift keying (QPSK) symbols to the resource elements (REs) of the first symbol. 
     Example 20 includes the subject matter of any one of examples 16-18, and further includes transmitting a signal in the first guard interval, and wherein the signal is a UL-DMRS or an AGC reference signal. 
     Example 21 includes the subject matter of examples 20, and further includes using a first half of a useful symbol length of the first symbol, generated based on a second half of the useful symbol length of the first symbol, as a part of a cyclic prefix for the first symbol; and mapping the UL-DMRS to a second half of the useful symbol length of the first symbol. 
     Example 22 includes the subject matter of examples 20, and further includes defining the AGC reference signal on a per-resource block or on a per-resource block set basis; and configuring a sequence that has a low peak-to-average-power-ratio (PAPR) and is common to a plurality of transmitting UEs, for the AGC reference signal. 
     Example 23 includes the subject matter of any one of examples 16-22, and further includes puncturing at least a part of a last symbol or the first symbol of the subframe as the second guard interval. 
     Example 24 is at least one storage medium having instructions configured to cause an apparatus, in response to execution of the instructions by the apparatus, to practice any subject matter of Examples 16-23. 
     Example 25 is an apparatus for wireless communication, which may include means to practice any subject matter of Examples 16-23. 
     Example 26 is a user equipment (UE) including a radio transceiver to communicate with another UE via device-to-device (D2D) communications; and processing circuitry, coupled to the radio transceiver, to schedule a D2D subframe to be transmitted at least 624 basic time units ahead of a corresponding reference time of the D2D subframe, wherein one basic time unit equals 1/30720000 seconds. 
     Example 27 includes the subject matter of example 26, wherein the corresponding reference time is a serving or camping cell downlink reference time in a time division duplex deployment. 
     Example 28 includes the subject matter of example 26 or 27, wherein the processing circuitry is to schedule the D2D subframe to be transmitted at 624 basic time units ahead of a serving or camping cell downlink reference time in a time division duplex deployment. 
     Example 29 includes the subject matter of example 26, wherein the corresponding reference time is a serving cell uplink reference time (SCURT) in a time division duplex deployment, wherein SCURT=SCDRT−TA, wherein SCDRT is a serving cell downlink reference time, and TA is an active timing advance value. 
     Example 30 includes the subject matter of any one of examples 26-29, wherein the processing circuitry is further to puncture a last symbol of the D2D subframe. 
     The description herein of illustrated implementations, including what is described in the Abstract, is not intended to be exhaustive or to limit the present disclosure to the precise forms disclosed. While specific implementations and examples are described herein for illustrative purposes, a variety of alternate and/or equivalent embodiments or implementations calculated to achieve the same purposes may be made in light of the above detailed description, without departing from the scope of the present disclosure, as those skilled in the relevant art will recognize.

Metadata:
Filing Date: 20190509
Publication Date: 20211005
Grant Date: 20211005
Priority Date: 20131127
Inventors: CHATTERJEE, Debdeep
HAN, SEUNGHEE
XIONG, GANG
NIU, HUANING
Assignee: APPLE INC
CPC Classifications: [{"code": "H04W72/51", "inventive": true, "first": false, "tree": "[]"}, {"code": "H04W72/23", "inventive": true, "first": false, "tree": "[]"}, {"code": "H04W72/21", "inventive": true, "first": false, "tree": "[]"}, {"code": "H04W16/24", "inventive": false, "first": false, "tree": "[]"}, {"code": "H04L27/2614", "inventive": true, "first": false, "tree": "[]"}, {"code": "H04L5/14", "inventive": true, "first": false, "tree": "[]"}, {"code": "H04L5/0078", "inventive": true, "first": false, "tree": "[]"}, {"code": "H04L5/0051", "inventive": true, "first": false, "tree": "[]"}, {"code": "H04L27/2607", "inventive": true, "first": false, "tree": "[]"}, {"code": "H04W72/0446", "inventive": true, "first": false, "tree": "[]"}, {"code": "H04W72/40", "inventive": true, "first": true, "tree": "[]"}, {"code": "H04W36/0083", "inventive": false, "first": false, "tree": "[]"}, {"code": "H04W36/0069", "inventive": true, "first": false, "tree": "[]"}, {"code": "H04W74/04", "inventive": true, "first": false, "tree": "[]"}, {"code": "H04W28/0205", "inventive": true, "first": false, "tree": "[]"}, {"code": "H04L27/2607", "inventive": true, "first": false, "tree": "[]"}, {"code": "H04L1/1825", "inventive": true, "first": false, "tree": "[]"}, {"code": "H04L1/0026", "inventive": true, "first": false, "tree": "[]"}, {"code": "H04W84/12", "inventive": false, "first": false, "tree": "[]"}, {"code": "H04W80/06", "inventive": false, "first": false, "tree": "[]"}, {"code": "H04W72/0446", "inventive": true, "first": false, "tree": "[]"}, {"code": "H04L1/1825", "inventive": true, "first": false, "tree": "[]"}, {"code": "H04L69/324", "inventive": true, "first": false, "tree": "[]"}, {"code": "H04W52/0216", "inventive": true, "first": false, "tree": "[]"}, {"code": "H04W40/30", "inventive": true, "first": false, "tree": "[]"}, {"code": "H04L69/161", "inventive": true, "first": false, "tree": "[]"}, {"code": "H04L5/14", "inventive": true, "first": false, "tree": "[]"}, {"code": "H04W88/10", "inventive": false, "first": false, "tree": "[]"}, {"code": "H04L5/0073", "inventive": true, "first": false, "tree": "[]"}, {"code": "H04L69/326", "inventive": true, "first": false, "tree": "[]"}, {"code": "H04L69/321", "inventive": true, "first": false, "tree": "[]"}, {"code": "H04L69/324", "inventive": true, "first": false, "tree": "[]"}, {"code": "H04L5/22", "inventive": true, "first": false, "tree": "[]"}, {"code": "H04L5/0078", "inventive": true, "first": false, "tree": "[]"}, {"code": "H04L69/161", "inventive": true, "first": false, "tree": "[]"}, {"code": "H04W80/06", "inventive": false, "first": false, "tree": "[]"}, {"code": "H04W52/0216", "inventive": true, "first": false, "tree": "[]"}, {"code": "H04L69/163", "inventive": true, "first": false, "tree": "[]"}, {"code": "H04L69/326", "inventive": true, "first": false, "tree": "[]"}, {"code": "H04W88/06", "inventive": false, "first": false, "tree": "[]"}, {"code": "H04W28/0205", "inventive": true, "first": false, "tree": "[]"}, {"code": "H04L69/321", "inventive": true, "first": false, "tree": "[]"}, {"code": "H04W76/27", "inventive": true, "first": false, "tree": "[]"}, {"code": "H04L5/0032", "inventive": true, "first": false, "tree": "[]"}, {"code": "H04B7/2621", "inventive": true, "first": false, "tree": "[]"}, {"code": "H04L5/0007", "inventive": true, "first": false, "tree": "[]"}, {"code": "Y02D30/50", "inventive": false, "first": false, "tree": "[]"}, {"code": "H04W72/0453", "inventive": true, "first": false, "tree": "[]"}, {"code": "H04W76/28", "inventive": true, "first": false, "tree": "[]"}, {"code": "H04L1/0026", "inventive": true, "first": false, "tree": "[]"}, {"code": "H04W52/0254", "inventive": true, "first": false, "tree": "[]"}, {"code": "H04L27/2607", "inventive": true, "first": false, "tree": "[]"}, {"code": "H04W72/02", "inventive": true, "first": false, "tree": "[]"}, {"code": "Y02D30/70", "inventive": false, "first": false, "tree": "[]"}, {"code": "H04W52/0254", "inventive": true, "first": false, "tree": "[]"}, {"code": "Y02D30/70", "inventive": false, "first": false, "tree": "[]"}, {"code": "H04L5/1469", "inventive": true, "first": false, "tree": "[]"}, {"code": "H04W40/30", "inventive": true, "first": false, "tree": "[]"}, {"code": "H04L5/0051", "inventive": true, "first": false, "tree": "[]"}, {"code": "H04W16/14", "inventive": true, "first": false, "tree": "[]"}, {"code": "H04L69/163", "inventive": true, "first": false, "tree": "[]"}, {"code": "H04L47/25", "inventive": true, "first": false, "tree": "[]"}, {"code": "H04L1/0026", "inventive": true, "first": true, "tree": "[]"}, {"code": "H04W74/04", "inventive": true, "first": true, "tree": "[]"}, {"code": "H04W88/06", "inventive": false, "first": false, "tree": "[]"}, {"code": "Y02D30/70", "inventive": false, "first": false, "tree": "[]"}, {"code": "H04W72/048", "inventive": true, "first": false, "tree": "[]"}, {"code": "H04W52/0254", "inventive": true, "first": false, "tree": "[]"}, {"code": "H04W72/0453", "inventive": true, "first": false, "tree": "[]"}, {"code": "H04L69/321", "inventive": true, "first": false, "tree": "[]"}, {"code": "H04W16/14", "inventive": true, "first": false, "tree": "[]"}, {"code": "H04W88/10", "inventive": false, "first": false, "tree": "[]"}, {"code": "H04L5/0007", "inventive": true, "first": false, "tree": "[]"}, {"code": "H04L5/0051", "inventive": true, "first": false, "tree": "[]"}, {"code": "H04L5/0073", "inventive": true, "first": false, "tree": "[]"}, {"code": "H04W72/0413", "inventive": true, "first": false, "tree": "[]"}, {"code": "H04W80/06", "inventive": false, "first": false, "tree": "[]"}, {"code": "Y02D30/50", "inventive": false, "first": false, "tree": "[]"}, {"code": "H04W72/0446", "inventive": true, "first": false, "tree": "[]"}, {"code": "H04L69/161", "inventive": true, "first": false, "tree": "[]"}, {"code": "H04W52/0216", "inventive": true, "first": false, "tree": "[]"}, {"code": "H04L47/25", "inventive": true, "first": false, "tree": "[]"}, {"code": "H04L1/0026", "inventive": true, "first": false, "tree": "[]"}, {"code": "H04W72/02", "inventive": true, "first": false, "tree": "[]"}, {"code": "H04L69/326", "inventive": true, "first": false, "tree": "[]"}, {"code": "H04L1/1825", "inventive": true, "first": false, "tree": "[]"}, {"code": "H04W72/042", "inventive": true, "first": false, "tree": "[]"}, {"code": "H04W74/04", "inventive": true, "first": true, "tree": "[]"}, {"code": "H04L69/163", "inventive": true, "first": false, "tree": "[]"}, {"code": "H04W36/0069", "inventive": true, "first": false, "tree": "[]"}, {"code": "H04W40/30", "inventive": true, "first": false, "tree": "[]"}, {"code": "H04W84/12", "inventive": false, "first": false, "tree": "[]"}, {"code": "H04L69/324", "inventive": true, "first": false, "tree": "[]"}, {"code": "H04B7/2621", "inventive": true, "first": false, "tree": "[]"}, {"code": "H04W76/28", "inventive": true, "first": false, "tree": "[]"}, {"code": "H04L5/14", "inventive": true, "first": false, "tree": "[]"}, {"code": "H04W76/27", "inventive": true, "first": false, "tree": "[]"}, {"code": "H04L27/2607", "inventive": true, "first": false, "tree": "[]"}, {"code": "H04L5/0032", "inventive": true, "first": false, "tree": "[]"}, {"code": "H04W28/0205", "inventive": true, "first": false, "tree": "[]"}, {"code": "H04B7/2621", "inventive": true, "first": true, "tree": "[]"}, {"code": "H04W36/0083", "inventive": false, "first": false, "tree": "[]"}, {"code": "H04W36/0069", "inventive": true, "first": false, "tree": "[]"}, {"code": "H04W36/0083", "inventive": false, "first": false, "tree": "[]"}, {"code": "H04W36/0069", "inventive": true, "first": false, "tree": "[]"}]
Family ID: 53182599