Patent Publication Number: US-2018049196-A1

Title: Combination of single-tone and multiple-tone signaling in sidelink communications

Description:
PRIORITY CLAIM 
     This application claims priority to and the benefit of provisional patent application no. 62/372,724, filed in the United States Patent and Trademark Office on Aug. 9, 2016, the entire content of which is incorporated herein by reference as if fully set forth below in its entirety and for all applicable purposes. 
    
    
     TECHNICAL FIELD 
     The technology discussed herein relates, generally, to wireless communication systems, and, more particularly, to wireless communication using a sidelink-centric slot. Embodiments can provide and enable techniques for reducing overhead in sidelink signaling. 
     INTRODUCTION 
     In many existing wireless communication systems, a cellular network is implemented by enabling wireless user equipment to communicate with another by signaling with a nearby base station or cell. As a user equipment moves across the service area, handovers take place such that each user equipment maintains communication with one another via its respective best cell. 
     Another scheme for a wireless communication system is frequently referred to as a mesh or peer to peer (P2P) network, whereby wireless user equipment may signal one another directly, rather than via an intermediary base station or cell. 
     Somewhat in between these schemes is a system configured for sidelink signaling. With sidelink signaling, a wireless user equipment communicates in a cellular system, generally under the control of a base station. However, the wireless user equipment is further configured for sidelink signaling directly between user equipment without passing through the base station. 
     As the demand for mobile broadband access continues to increase, research and development continue to advance wireless communication technologies not only to meet the growing demand for mobile broadband access, but to advance and enhance the user experience with mobile communications. 
     BRIEF SUMMARY OF SOME EXAMPLES 
     The following presents a simplified summary of one or more aspects of the present disclosure, in order to provide a basic understanding of such aspects. This summary is not an extensive overview of all contemplated features of the disclosure, and is intended neither to identify key or critical elements of all aspects of the disclosure nor to delineate the scope of any or all aspects of the disclosure. Its sole purpose is to present some concepts of one or more aspects of the disclosure in a simplified form as a prelude to the more detailed description that is presented later. 
     Various aspects of the present disclosure describe a sidelink signaling mechanism that provides for a combination of single-tone and multiple-tone signaling to reduce overhead, while ensuring reliable signaling. In some examples, a sidelink request signal, such as one or more of a direction selection signal (DSS) and a source transmit signal (STS) signal, may be a single-tone signal, and a sidelink confirmation signal, such as a destination receive signal (DRS), may be a multiple-tone signal. In other examples, the request signal may be a multiple-tone signal (e.g., at least the STS), while the confirmation signal may be a single-tone signal. In some examples, the single-tone signals are analog signals, while the multiple-tone signals are digital signals. 
     In one aspect of the disclosure, a method of sidelink wireless communication is disclosed. The method includes transmitting a request signal indicating a requested duration of time for a transmitting device to utilize a sidelink channel to transmit a sidelink signal, and receiving a confirmation signal from a receiving device indicating availability of the sidelink channel for the requested duration of time. One of the request signal or the confirmation signal is a single-tone signal, while the other is a multiple-tone signal. 
     Another aspect of the disclosure provides a device for sidelink wireless communication. The device includes a processor, a transceiver communicatively coupled to the processor, and a memory communicatively coupled to the processor. The processor is configured to transmit a request signal indicating a requested duration of time for the device to utilize a sidelink channel to transmit a sidelink signal, and receive a confirmation signal from an additional device indicating availability of the sidelink channel for the requested duration of time. One of the request signal or the confirmation signal is a single-tone signal, while the other is a multiple-tone signal. 
     Another aspect of the disclosure provides an apparatus for sidelink wireless communication. The apparatus includes means for transmitting a request signal indicating a requested duration of time for a transmitting device to utilize a sidelink channel to transmit a sidelink signal, and means for receiving a confirmation signal from a receiving device indicating availability of the sidelink channel for the requested duration of time. One of the request signal or the confirmation signal is a single-tone signal, while the other is a multiple-tone signal. 
     Examples of additional aspects of the disclosure follow. In some aspects of the disclosure, the request signal includes a primary request signal, such as the DSS, and a secondary request signal, such as the STS signal. The transmitting device may transmit the primary request signal when the transmitting device is a primary device to indicate link direction. 
     In some aspects of the disclosure, at least one of the primary and secondary request signals is a single-tone signal, and the confirmation signal, such as the DRS signal, is the multiple-tone signal. In examples where both the primary and secondary request signals are single-tone signals, the secondary request signal may include a destination identifier (ID) of the receiving device. For example, the secondary request signal may include a tone ID indicating the destination ID. In this example, the transmitting device may associate with the receiving device and select the tone ID for the receiving device. In addition, the requested duration of time for utilizing the sidelink channel may be fixed. 
     In examples where the confirmation signal is the multiple-tone signal and at least one of the primary and secondary request signals are single-tone signals, the confirmation signal may include channel quality information (CQI). In some examples, the multiple-tone confirmation signal may include one or more of a signal-to interference-plus-noise ratio (SINR), CQI, a reference signal or a power setting selected to control dimensions of a protection zone and manage interference for the sidelink signal. In some examples, both the confirmation signal and the primary request signal are multiple-tone signals and the secondary request signal is a single-tone signal. In this example, the transmitting device may further transmit a reference signal to enable channel estimation by the receiving device. 
     In some aspects of the disclosure, the secondary request signal is a multiple-tone signal, the confirmation signal is a single-tone signal or a multiple-tone signal, and the primary request signal is a single-tone signal or a multiple-tone signal. In examples where the confirmation signal is a single-tone signal and the secondary request signal is a multiple-tone signal, the single-tone confirmation signal includes a power set to control dimensions of a protection zone and manage interference for the sidelink signal. 
     These and other aspects of the invention will become more fully understood upon a review of the detailed description, which follows. Other aspects, features, and embodiments of the present invention will become apparent to those of ordinary skill in the art, upon reviewing the following description of specific, exemplary embodiments of the present invention in conjunction with the accompanying figures. While features of the present invention may be discussed relative to certain embodiments and figures below, all embodiments of the present invention can include one or more of the advantageous features discussed herein. In other words, while one or more embodiments may be discussed as having certain advantageous features, one or more of such features may also be used in accordance with the various embodiments of the invention discussed herein. In similar fashion, while exemplary embodiments may be discussed below as device, system, or method embodiments it should be understood that such exemplary embodiments can be implemented in various devices, systems, and methods. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a diagram illustrating an example of an access network according to some aspects of the present disclosure. 
         FIG. 2  is a diagram conceptually illustrating an example of a scheduling entity communicating with one or more scheduled entities according to some aspects of the present disclosure. 
         FIG. 3  is a diagram illustrating an example of a hardware implementation for a scheduling entity according to some aspects of the present disclosure. 
         FIG. 4  is a diagram illustrating an example of a hardware implementation for a scheduled entity according to some aspects of the present disclosure. 
         FIG. 5  is a diagram illustrating an example of a downlink (DL)-centric slot according to some aspects of the present disclosure. 
         FIG. 6  is a diagram illustrating an example of an uplink (UL)-centric slot according to some aspects of the present disclosure. 
         FIG. 7  is a diagram illustrating an example of a sidelink-centric slot according to some aspects of the present disclosure. 
         FIG. 8  is a diagram illustrating an example of multiple concurrent sidelink-centric slots according to some aspects of the present disclosure. 
         FIG. 9  is a diagram illustrating another example of a sidelink-centric slot according to some aspects of the present disclosure. 
         FIG. 10  is a diagram illustrating another example of multiple concurrent sidelink-centric slots according to some aspects of the present disclosure. 
         FIG. 11  is a diagram illustrating yet another example of multiple concurrent sidelink-centric slots according to some aspects of the present disclosure. 
         FIG. 12  is a diagram illustrating an example of a sidelink-centric slot that utilizes a combination of single-tone and multiple-tone signaling according to some aspects of the present disclosure. 
         FIG. 13  is a diagram illustrating another example of a sidelink-centric slot that utilizes a combination of single-tone and multiple-tone signaling according to some aspects of the present disclosure. 
         FIG. 14  is a diagram illustrating another example of a sidelink-centric slot that utilizes a combination of single-tone and multiple-tone signaling according to some aspects of the present disclosure. 
         FIG. 15  is a flow chart illustrating a process for single-tone and multiple-tone sidelink signaling according to some embodiments. 
         FIG. 16  is a flow chart illustrating another process for single-tone and multiple-tone sidelink signaling according to some embodiments. 
         FIG. 17  is a flow chart illustrating a process for utilizing a single-tone request signal in sidelink communications according to some embodiments. 
         FIG. 18  is a flow chart illustrating a process for utilizing single-tone and multiple-tone sidelink signaling to control the dimensions of a protection zone according to some embodiments. 
     
    
    
     DETAILED DESCRIPTION 
     The detailed description set forth below in connection with the appended drawings is intended as a description of various configurations and is not intended to represent the only configurations in which the concepts described herein may be practiced. The detailed description includes specific details for the purpose of providing a thorough understanding of various concepts. However, it will be apparent to those skilled in the art that these concepts may be practiced without these specific details. In some instances, well known structures and components are shown in block diagram form in order to avoid obscuring such concepts. 
     The various concepts presented throughout this disclosure may be implemented across a broad variety of telecommunication systems, network architectures, and communication standards. Referring now to  FIG. 1 , as an illustrative example without limitation, a simplified schematic illustration of an access network  100  is provided. 
     The geographic region covered by the access network  100  may be divided into a number of cellular regions (cells) that can be uniquely identified by a user equipment (UE) based on an identification broadcasted over a geographical from one access point or base station.  FIG. 1  illustrates macrocells  102 ,  104 , and  106 , and a small cell  108 , each of which may include one or more sectors. A sector is a sub-area of a cell. All sectors within one cell are served by the same base station. A radio link within a sector can be identified by a single logical identification belonging to that sector. In a cell that is divided into sectors, the multiple sectors within a cell can be formed by groups of antennas with each antenna responsible for communication with UEs in a portion of the cell. 
     In general, a base station (BS) serves each cell. Broadly, a base station is a network element in a radio access network responsible for radio transmission and reception in one or more cells to or from a UE. A BS may also be referred to by those skilled in the art as a base transceiver station (BTS), a radio base station, a radio transceiver, a transceiver function, a basic service set (BSS), an extended service set (ESS), an access point (AP), a Node B (NB), an eNode B (eNB), a GNodeB or some other suitable terminology. 
     In  FIG. 1 , two high-power base stations  110  and  112  are shown in cells  102  and  104 ; and a third high-power base station  114  is shown controlling a remote radio head (RRH)  116  in cell  106 . That is, a base station can have an integrated antenna or can be connected to an antenna or RRH by feeder cables. In the illustrated example, the cells  102 ,  104 , and  106  may be referred to as macrocells, as the high-power base stations  110 ,  112 , and  114  support cells having a large size. Further, a low-power base station  118  is shown in the small cell  108  (e.g., a microcell, picocell, femtocell, home base station, home Node B, home eNode B, etc.) which may overlap with one or more macrocells. In this example, the cell  108  may be referred to as a small cell, as the low-power base station  118  supports a cell having a relatively small size. Cell sizing can be done according to system design as well as component constraints. It is to be understood that the access network  100  may include any number of wireless base stations and cells. Further, a relay node may be deployed to extend the size or coverage area of a given cell. The base stations  110 ,  112 ,  114 ,  118  provide wireless access points to a core network for any number of mobile apparatuses. 
       FIG. 1  further includes a quadcopter or drone  120 , which may be configured to function as a base station. That is, in some examples, a cell may not necessarily be stationary, and the geographic area of the cell may move according to the location of a mobile base station such as the quadcopter  120 . 
     In general, base stations may include a backhaul interface for communication with a backhaul portion of the network. The backhaul may provide a link between a base station and a core network, and in some examples, the backhaul may provide interconnection between the respective base stations. The core network is a part of a wireless communication system that is generally independent of the radio access technology used in the radio access network. Various types of backhaul interfaces may be employed, such as a direct physical connection, a virtual network, or the like using any suitable transport network. Some base stations may be configured as integrated access and backhaul (IAB) nodes, where the wireless spectrum may be used both for access links (i.e., wireless links with UEs), and for backhaul links. This scheme is sometimes referred to as wireless self-backhauling. By using wireless self-backhauling, rather than requiring each new base station deployment to be outfitted with its own hard-wired backhaul connection, the wireless spectrum utilized for communication between the base station and UE may be leveraged for backhaul communication, enabling fast and easy deployment of highly dense small cell networks. 
     The access network  100  is illustrated supporting wireless communication for multiple mobile apparatuses. A mobile apparatus is commonly referred to as user equipment (UE) in standards and specifications promulgated by the 3rd Generation Partnership Project (3GPP), but may also be referred to by those skilled in the art as a mobile station (MS), a subscriber station, a mobile unit, a subscriber unit, a wireless unit, a remote unit, a mobile device, a wireless device, a wireless communications device, a remote device, a mobile subscriber station, an access terminal (AT), a mobile terminal, a wireless terminal, a remote terminal, a handset, a terminal, a user agent, a mobile client, a client, or some other suitable terminology. A UE may be an apparatus that provides a user with access to network services. 
     Within the present document, a “mobile” apparatus need not necessarily have a capability to move, and may be stationary. The term mobile apparatus or mobile device broadly refers to a diverse array of devices and technologies. For example, some non-limiting examples of a mobile apparatus include a mobile, a cellular (cell) phone, a smart phone, a session initiation protocol (SIP) phone, a laptop, a personal computer (PC), a notebook, a netbook, a smartbook, a tablet, a personal digital assistant (PDA), and a broad array of embedded systems, e.g., corresponding to an “Internet of things” (IoT). A mobile apparatus may additionally be an automotive or other transportation vehicle, a remote sensor or actuator, a robot or robotics device, a satellite radio, a global positioning system (GPS) device, an object tracking device, a drone, a multi-copter, a quad-copter, a remote control device, a consumer and/or wearable device, such as eyewear, a wearable camera, a virtual reality device, a smart watch, a health or fitness tracker, a digital audio player (e.g., MP3 player), a camera, a game console, etc. A mobile apparatus may additionally be a digital home or smart home device such as a home audio, video, and/or multimedia device, an appliance, a vending machine, intelligent lighting, a home security system, a smart meter, etc. A mobile apparatus may additionally be a smart energy device, a security device, a solar panel or solar array, a municipal infrastructure device controlling electric power (e.g., a smart grid), lighting, water, etc.; an industrial automation and enterprise device; a logistics controller; agricultural equipment; military defense equipment, vehicles, aircraft, ships, and weaponry, etc. Still further, a mobile apparatus may provide for connected medicine or telemedicine support, i.e., health care at a distance. Telehealth devices may include telehealth monitoring devices and telehealth administration devices, whose communication may be given preferential treatment or prioritized access over other types of information, e.g., in terms of prioritized access for transport of critical service user data traffic, and/or relevant QoS for transport of critical service user data traffic. 
     Within the access network  100 , the cells may include UEs that may be in communication with one or more sectors of each cell. For example, UEs  122  and  124  may be in communication with base station  110 ; UEs  126  and  128  may be in communication with base station  112 ; UEs  130  and  132  may be in communication with base station  114  by way of RRH  116 ; UE  134  may be in communication with low-power base station  118 ; and UE  136  may be in communication with mobile base station  120 . Here, each base station  110 ,  112 ,  114 ,  118 , and  120  may be configured to provide an access point to a core network (not shown) for all the UEs in the respective cells. 
     In another example, a mobile network node (e.g., quadcopter  120 ) may be configured to function as a UE. For example, the quadcopter  120  may operate within cell  102  by communicating with base station  110 . In some aspects of the disclosure, two or more UE (e.g., UEs  126  and  128 ) may communicate with each other using peer to peer (P2P) or sidelink signals  127  without relaying that communication through a base station (e.g., base station  112 ). 
     Unicast or broadcast transmissions of control information and/or traffic information from a base station (e.g., base station  110 ) to one or more UEs (e.g., UEs  122  and  124 ) may be referred to as downlink (DL) transmission, while transmissions of control information and/or traffic information originating at a UE (e.g., UE  122 ) may be referred to as uplink (UL) transmissions. In addition, the uplink and/or downlink control information and/or traffic information may be time-divided into frames, subframes, slots, and/or symbols. As used herein, a symbol may refer to a unit of time that, in an OFDM waveform, carries one resource element (RE) per subcarrier. A slot may carry  7  or 14 OFDM symbols. A subframe may refer to a duration of 1 ms. Multiple subframes may be grouped together to form a single frame or radio frame. Of course, these definitions are not required, and any suitable scheme for organizing waveforms may be utilized, and various time divisions of the waveform may have any suitable duration. 
     The air interface in the access network  100  may utilize one or more multiplexing and multiple access algorithms to enable simultaneous communication of the various devices. For example, multiple access for uplink (UL) or reverse link transmissions from UEs  122  and  124  to base station  110  may be provided utilizing time division multiple access (TDMA), code division multiple access (CDMA), frequency division multiple access (FDMA), orthogonal frequency division multiple access (OFDMA), sparse code multiple access (SCMA), single-carrier frequency division multiple access (SC-FDMA), resource spread multiple access (RSMA), or other suitable multiple access schemes. Further, multiplexing downlink (DL) or forward link transmissions from the base station  110  to UEs  122  and  124  may be provided utilizing time division multiplexing (TDM), code division multiplexing (CDM), frequency division multiplexing (FDM), orthogonal frequency division multiplexing (OFDM), sparse code multiplexing (SCM), single-carrier frequency division multiplexing (SC-FDM) or other suitable multiplexing schemes. 
     Further, the air interface in the access network  100  may utilize one or more duplexing algorithms Duplex refers to a point-to-point communication link where both endpoints can communicate with one another in both directions. Full duplex means both endpoints can simultaneously communicate with one another. Half duplex means only one endpoint can send information to the other at a time. In a wireless link, a full duplex channel generally relies on physical isolation of a transmitter and receiver, and suitable interference cancellation technologies. Full duplex emulation is frequently implemented for wireless links by utilizing frequency division duplex (FDD) or time division duplex (TDD). In FDD, transmissions in different directions operate at different carrier frequencies. In TDD, transmissions in different directions on a given channel are separated from one another using time division multiplexing. That is, at some times the channel is dedicated for transmissions in one direction, while at other times the channel is dedicated for transmissions in the other direction, where the direction may change very rapidly, e.g., several times per subframe. 
     In the radio access network  100 , the ability for a UE to communicate while moving, independent of their location, is referred to as mobility. The various physical channels between the UE and the radio access network are generally set up, maintained, and released under the control of a mobility management entity (MME). In various aspects of the disclosure, an access network  100  may utilize DL-based mobility or UL-based mobility to enable mobility and handovers (i.e., the transfer of a UE&#39;s connection from one radio channel to another). In a network configured for DL-based mobility, during a call with a scheduling entity, or at any other time, a UE may monitor various parameters of the signal from its serving cell as well as various parameters of neighboring cells. Depending on the quality of these parameters, the UE may maintain communication with one or more of the neighboring cells. During this time, if the UE moves from one cell to another, or if signal quality from a neighboring cell exceeds that from the serving cell for a given amount of time, the UE may undertake a handoff or handover from the serving cell to the neighboring (target) cell. For example, UE  124  may move from the geographic area corresponding to its serving cell  102  to the geographic area corresponding to a neighbor cell  106 . When the signal strength or quality from the neighbor cell  106  exceeds that of its serving cell  102  for a given amount of time, the UE  124  may transmit a reporting message to its serving base station  110  indicating this condition. In response, the UE  124  may receive a handover command, and the UE may undergo a handover to the cell  106 . 
     In a network configured for UL-based mobility, UL reference signals from each UE may be utilized by the network to select a serving cell for each UE. In some examples, the base stations  110 ,  112 , and  114 / 116  may broadcast unified synchronization signals (e.g., unified Primary Synchronization Signals (PSSs), unified Secondary Synchronization Signals (SSSs) and unified Physical Broadcast Channels (PBCH)). The UEs  122 ,  124 ,  126 ,  128 ,  130 , and  132  may receive the unified synchronization signals, derive the carrier frequency and slot timing from the synchronization signals, and in response to deriving timing, transmit an uplink pilot or reference signal. The uplink pilot signal transmitted by a UE (e.g., UE  124 ) may be concurrently received by two or more cells (e.g., base stations  110  and  114 / 116 ) within the access network  100 . Each of the cells may measure a strength of the pilot signal, and the access network (e.g., one or more of the base stations  110  and  114 / 116  and/or a central node within the core network) may determine a serving cell for the UE  124 . As the UE  124  moves through the access network  100 , the network may continue to monitor the uplink pilot signal transmitted by the UE  124 . When the signal strength or quality of the pilot signal measured by a neighboring cell exceeds that of the signal strength or quality measured by the serving cell, the network  100  may handover the UE  124  from the serving cell to the neighboring cell, with or without informing the UE  124 . 
     Although the synchronization signal transmitted by the base stations  110 ,  112 , and  114 / 116  may be unified, the synchronization signal may not identify a particular cell, but rather may identify a zone of multiple cells operating on the same frequency and/or with the same timing. The use of zones in 5G networks or other next generation communication networks enables the uplink-based mobility framework and improves the efficiency of both the UE and the network, since the number of mobility messages that need to be exchanged between the UE and the network may be reduced. 
     In various implementations, the air interface in the access network  100  may utilize licensed spectrum, unlicensed spectrum, or shared spectrum. Licensed spectrum provides for exclusive use of a portion of the spectrum, generally by virtue of a mobile network operator purchasing a license from a government regulatory body. Unlicensed spectrum provides for shared use of a portion of the spectrum without need for a government-granted license. While compliance with some technical rules is generally still required to access unlicensed spectrum, generally, any operator or device may gain access. Shared spectrum may fall between licensed and unlicensed spectrum, wherein technical rules or limitations may be required to access the spectrum, but the spectrum may still be shared by multiple operators and/or multiple RATs. For example, the holder of a license for a portion of licensed spectrum may provide licensed shared access (LSA) to share that spectrum with other parties, e.g., with suitable licensee-determined conditions to gain access. 
     In some examples, access to the air interface may be scheduled, wherein a scheduling entity (e.g., a base station) allocates resources (e.g., time-frequency resources) for communication among some or all devices and equipment within its service area or cell. Within the present disclosure, as discussed further below, the scheduling entity may be responsible for scheduling, assigning, reconfiguring, and releasing resources for one or more scheduled entities. That is, for scheduled communication, UEs or scheduled entities utilize resources allocated by the scheduling entity. 
     Base stations are not the only entities that may function as a scheduling entity. 
     That is, in some examples, a UE may function as a scheduling entity, scheduling resources for one or more scheduled entities (e.g., one or more other UEs). In other examples, sidelink signals may be used between UEs without necessarily relying on scheduling or control information from a base station. For example, UE  138  is illustrated communicating with UEs  140  and  142 . In some examples, the UE  138  is functioning as a scheduling entity or a primary sidelink device, and UEs  140  and  142  may function as a scheduled entity or a non-primary (e.g., secondary) sidelink device. In still another example, a UE may function as a scheduling entity in a device-to-device (D2D), peer-to-peer (P2P), or vehicle-to-vehicle (V2V) network, and/or in a mesh network. In a mesh network example, UEs  140  and  142  may optionally communicate directly with one another in addition to communicating with the scheduling entity  138 . 
     Thus, in a wireless communication network with scheduled access to time-frequency resources and having a cellular configuration, a P2P configuration, or a mesh configuration, a scheduling entity and one or more scheduled entities may communicate utilizing the scheduled resources. Referring now to  FIG. 2 , a block diagram illustrates a scheduling entity  202  and a plurality of scheduled entities  204  (e.g.,  204   a  and  204   b ). Here, the scheduling entity  202  may correspond to a base station  110 ,  112 ,  114 , and/or  118 . In additional examples, the scheduling entity  202  may correspond to a UE  138 , the quadcopter  120 , or any other suitable node in the radio access network  100 . Similarly, in various examples, the scheduled entity  204  may correspond to the UE  122 ,  124 ,  126 ,  128 ,  130 ,  132 ,  134 ,  136 ,  138 ,  140 , and  142 , or any other suitable node in the radio access network  100 . 
     As illustrated in  FIG. 2 , the scheduling entity  202  may broadcast user data traffic  206  to one or more scheduled entities  204  (the user data traffic may be referred to as downlink user data traffic). In accordance with certain aspects of the present disclosure, the term downlink may refer to a point-to-multipoint transmission originating at the scheduling entity  202 . Broadly, the scheduling entity  202  is a node or device responsible for scheduling user data traffic in a wireless communication network, including the downlink transmissions and, in some examples, uplink user data traffic  210  from one or more scheduled entities to the scheduling entity  202 . Another way to describe the system may be to use the term broadcast channel multiplexing. In accordance with aspects of the present disclosure, the term uplink may refer to a point-to-point transmission originating at a scheduled entity  204 . Broadly, the scheduled entity  204  is a node or device that receives scheduling control information, including but not limited to scheduling grants, synchronization or timing information, or other control information from another entity in the wireless communication network such as the scheduling entity  202 . 
     The scheduling entity  202  may broadcast control information  208  including one or more control channels, such as a PBCH; a PSS; a SSS; a physical control format indicator channel (PCFICH); a physical hybrid automatic repeat request (HARQ) indicator channel (PHICH); and/or a physical downlink control channel (PDCCH), etc., to one or more scheduled entities  204 . The PHICH carries HARQ feedback transmissions such as an acknowledgment (ACK) or negative acknowledgment (NACK). HARQ is a technique well known to those of ordinary skill in the art, wherein packet transmissions may be checked at the receiving side for accuracy, and if confirmed, an ACK may be transmitted, whereas if not confirmed, a NACK may be transmitted. In response to a NACK, the transmitting device may send a HARQ retransmission, which may implement chase combining, incremental redundancy, etc. 
     Uplink user data traffic  210  and/or downlink user data traffic  206  including one or more traffic channels, such as a physical downlink shared channel (PDSCH) or a physical uplink shared channel (PUSCH) (and, in some examples, system information blocks (SIBs)), may additionally be transmitted between the scheduling entity  202  and the scheduled entity  204 . Transmissions of the control and user data traffic information may be organized by subdividing a carrier, in time, into suitable slots. 
     Furthermore, the scheduled entities  204  may transmit uplink control information  212  including one or more uplink control channels (e.g, the physical uplink control channel (PUCCH)) to the scheduling entity  202 . Uplink control information (UCI) transmitted within the PUCCH may include a variety of packet types and categories, including pilots, reference signals, and information configured to enable or assist in decoding uplink traffic transmissions. In some examples, the control information  212  may include a scheduling request (SR), i.e., request for the scheduling entity  202  to schedule uplink transmissions. Here, in response to the SR transmitted on the control channel  212 , the scheduling entity  202  may transmit downlink control information  208  that may schedule the slot for uplink packet transmissions. 
     Uplink and downlink transmissions may generally utilize a suitable error correcting block code. In a typical block code, an information message or sequence is split up into information blocks, and an encoder at the transmitting device then mathematically adds redundancy to the information message. Exploitation of this redundancy in the encoded information message can improve the reliability of the message, enabling correction for any bit errors that may occur due to the noise. Some examples of error correcting codes include Hamming codes, Bose-Chaudhuri-Hocquenghem (BCH) codes, turbo codes, low-density parity check (LDPC) codes, Walsh codes, and polar codes. Various implementations of scheduling entities  202  and scheduled entities  204  may include suitable hardware and capabilities (e.g., an encoder and/or decoder) to utilize any one or more of these error correcting codes for wireless communication. 
     In some examples, scheduled entities such as a first scheduled entity  204   a  and a second scheduled entity  204   b  may utilize sidelink signals for direct D2D communication. Sidelink signals may include sidelink user data traffic  214  and sidelink control  216 . Sidelink control information  216  may include a source transmit signal (STS), a direction selection signal (DSS), a destination receive signal (DRS), and a physical sidelink HARQ indicator channel (PSHICH). The DSS/STS may provide for a scheduled entity  204  to request a duration of time to keep a sidelink channel available for a sidelink signal; and the DRS may provide for the scheduled entity  204  to indicate availability of the sidelink channel, e.g., for a requested duration of time. An exchange of DSS/STS and DRS (e.g., handshake) may enable different scheduled entities performing sidelink communications to negotiate the availability of the sidelink channel prior to communication of the sidelink user data traffic  214 . The PSHICH may include HARQ acknowledgment information and/or a HARQ indicator from a destination device, so that the destination may acknowledge traffic received from a source device. 
     The channels or carriers illustrated in  FIG. 2  are not necessarily all of the channels or carriers that may be utilized between a scheduling entity  202  and scheduled entities  204 , and those of ordinary skill in the art will recognize that other channels or carriers may be utilized in addition to those illustrated, such as other traffic, control, and feedback channels. 
       FIG. 3  is a diagram  300  illustrating an example of a hardware implementation for scheduling entity  202  according to aspects of the present disclosure. Scheduling entity  202  may employ a processing system  314 . Scheduling entity  202  may be implemented with a processing system  314  that includes one or more processors  304 . Examples of processors  304  include microprocessors, microcontrollers, digital signal processors (DSPs), field programmable gate arrays (FPGAs), programmable logic devices (PLDs), state machines, gated logic, discrete hardware circuits, and other suitable hardware configured to perform the various functionality described throughout this disclosure. In various examples, scheduling entity  202  may be configured to perform any one or more of the functions described herein. That is, the processor  304 , as utilized in scheduling entity  202 , may be used or configured to implement any one or more of the processes described herein. 
     In this example, the processing system  314  may be implemented with a bus architecture, represented generally by the bus  302 . The bus  302  may include any number of interconnecting buses and bridges depending on the specific application of the processing system  314  and the overall design constraints. The bus  302  communicatively couples together various circuits including one or more processors (represented generally by the processor  304 ), a memory  305 , and computer-readable media (represented generally by the computer-readable medium  306 ). The bus  302  may also link various other circuits such as timing sources, peripherals, voltage regulators, and power management circuits. A bus interface  308  provides an interface between the bus  302  and a transceiver  310 . The transceiver  310  provides a communication interface or a means for communicating with various other apparatuses over a transmission medium. Depending upon the nature of the apparatus, a user interface  312  (e.g., keypad, display, speaker, microphone, joystick) may also be provided. 
     At least one processor  304  is responsible for managing the bus  302  and general processing, including the execution of software stored on the computer-readable medium  306 . The software, when executed by the processor  304 , causes the processing system  314  to perform the various functions described below for any particular apparatus. The computer-readable medium  306  and the memory  305  may also be used for storing data that is manipulated by the processor  304  when executing software. In some aspects of the disclosure, the computer-readable medium  306  may include communication instructions  352 . The communication instructions  352  may include instructions for performing various operations related to wireless communication (e.g., signal reception and/or signal transmission) as described herein. For example, the communication instructions  352  may include code for configuring the processing system  314  and communication interface  310  to communicate and control a plurality of scheduled entities using sidelink communication. In some aspects of the disclosure, the computer-readable medium  306  may include processing instructions  354 . The processing instructions  354  may include instructions for performing various operations related to signal processing (e.g., processing a received signal and/or processing a signal for transmission) as described herein. In one example, the processing instructions  354  include code that may be executed by the processor  304  to control and schedule sidelink communication as described in  FIGS. 7-18 . 
     At least one processor  304  may execute software. Software shall be construed broadly to mean instructions, instruction sets, code, code segments, program code, programs, subprograms, software modules, applications, software applications, software packages, routines, subroutines, objects, executables, threads of execution, procedures, functions, etc., whether referred to as software, firmware, middleware, microcode, hardware description language, or otherwise. The software may reside on a computer-readable medium  306 . The computer-readable medium  306  may be a non-transitory computer-readable medium. A non-transitory computer-readable medium includes, by way of example, a magnetic storage device (e.g., hard disk, floppy disk, magnetic strip), an optical disk (e.g., a compact disc (CD) or a digital versatile disc (DVD)), a smart card, a flash memory device (e.g., a card, a stick, or a key drive), a random access memory (RAM), a read only memory (ROM), a programmable ROM (PROM), an erasable PROM (EPROM), an electrically erasable PROM (EEPROM), a register, a removable disk, and any other suitable medium for storing software and/or instructions that may be accessed and read by a computer. The computer-readable medium may also include, by way of example, a carrier wave, a transmission line, and any other suitable medium for transmitting software and/or instructions that may be accessed and read by a computer. The computer-readable medium  306  may reside in the processing system  314 , external to the processing system  314 , or distributed across multiple entities including the processing system  314 . The computer-readable medium  306  may be embodied in a computer program product. By way of example, a computer program product may include a computer-readable medium in packaging materials. Those skilled in the art will recognize how best to implement the described functionality presented throughout this disclosure depending on the particular application and the overall design constraints imposed on the overall system. 
     In some aspects of the disclosure, at least one processor  304  may include a communication circuit  342 . The communication circuit  342  may include one or more hardware components that provide the physical structure that performs various processes related to wireless communication (e.g., signal reception and/or signal transmission) as described herein. For example, the communication circuit  340  may be configured to control and schedule sidelink communication among a plurality of scheduled entities. The communication circuit  342  may transmit or broadcast sidelink grants or control information to the scheduled entities using a downlink control channel (e.g., PDCCH) via the communication interface  310 . In some aspects of the disclosure, the processor  304  may also include a processing circuit  344 . The processing circuit  344  may include one or more hardware components that provide the physical structure that performs various processes related to signal processing (e.g., processing a received signal and/or processing a signal for transmission) as described herein. The circuitry included in the processor  304  is provided as non-limiting examples. Other means for carrying out the described functions exists and is included within various aspects of the present disclosure. In some aspects of the disclosure, the computer-readable medium  306  may store computer-executable code comprising instructions configured to perform various processes described herein. The instructions included in the computer-readable medium  306  are provided as non-limiting examples. Other instructions configured to carry out the described functions exist and are included within various aspects of the present disclosure. 
       FIG. 4  is a diagram  400  illustrating an example of a hardware implementation for a scheduled entity  204  according to aspects of the present disclosure. The scheduled entity  204  may employ a processing system  414 . The scheduled entity  204  may be implemented with a processing system  414  that includes one or more processors  404 . For example, the scheduled entity  204  may be a user equipment (UE) as illustrated in any one or more of  FIGS. 1 and/or 2 . 
     Examples of processors  404  include microprocessors, microcontrollers, DSPs, FPGAs, PLDs, state machines, gated logic, discrete hardware circuits, and other suitable hardware configured to perform the various functionality described throughout this disclosure. In various examples, scheduled entity  204  may be configured to perform any one or more of the functions described herein. That is, the processor  404 , as utilized in scheduled entity  204 , may be used or configured to implement any one or more of the processes described herein, for example, in  FIGS. 7-18 . 
     In this example, the processing system  414  may be implemented with a bus architecture, represented generally by the bus  402 . The bus  402  may include any number of interconnecting buses and bridges depending on the specific application of the processing system  414  and the overall design constraints. The bus  402  communicatively couples together various circuits including one or more processors (represented generally by the processor  404 ), a memory  405 , and computer-readable media (represented generally by the computer-readable medium  406 ). The bus  402  may also link various other circuits such as timing sources, peripherals, voltage regulators, and power management circuits. A bus interface  408  provides an interface between the bus  402  and a transceiver  410 . The transceiver  410  provides a communication interface or a means for communicating with various other apparatuses over a transmission medium. Depending upon the nature of the apparatus, a user interface  412  (e.g., keypad, display, speaker, microphone, joystick) may also be provided. 
     At least one processor  404  is responsible for managing the bus  402  and general processing, including the execution of software stored on the computer-readable medium  406 . The software, when executed by the processor  404 , causes the processing system  414  to perform the various functions described below for any particular apparatus. The computer-readable medium  406  and the memory  405  may also be used for storing data that is manipulated by the processor  404  when executing software. In some aspects of the disclosure, the computer-readable medium  406  may include communication instructions  452 . The communication instructions  452  may include instructions for performing various operations related to wireless communication (e.g., signal reception and/or signal transmission) as described herein. In some aspects of the disclosure, the instructions  452  may include code for configuring the scheduled entity to perform sidelink communication as described in relation to  FIGS. 7-18 . In some aspects of the disclosure, the computer-readable medium  406  may include processing instructions  454 . The processing instructions  454  may include instructions for performing various operations related to signal processing (e.g., processing a received signal and/or processing a signal for transmission) as described herein. In some aspects of the disclosure, the processing instructions  454  may include code for configuring the scheduled entity to perform sidelink communication as described in relation to  FIGS. 7-18 . 
     At least one processor  404  may execute software. Software shall be construed broadly to mean instructions, instruction sets, code, code segments, program code, programs, subprograms, software modules, applications, software applications, software packages, routines, subroutines, objects, executables, threads of execution, procedures, functions, etc., whether referred to as software, firmware, middleware, microcode, hardware description language, or otherwise. The software may reside on a computer-readable medium  406 . The computer-readable medium  406  may be a non-transitory computer-readable medium. A non-transitory computer-readable medium includes, by way of example, a magnetic storage device (e.g., hard disk, floppy disk, magnetic strip), an optical disk (e.g., a CD or a DVD), a smart card, a flash memory device (e.g., a card, a stick, or a key drive), a RAM, a ROM, a PROM, an EPROM, an EEPROM, a register, a removable disk, and any other suitable medium for storing software and/or instructions that may be accessed and read by a computer. The computer-readable medium may also include, by way of example, a carrier wave, a transmission line, and any other suitable medium for transmitting software and/or instructions that may be accessed and read by a computer. The computer-readable medium  406  may reside in the processing system  414 , external to the processing system  414 , or distributed across multiple entities including the processing system  414 . The computer-readable medium  406  may be embodied in a computer program product. By way of example, a computer program product may include a computer-readable medium in packaging materials. Those skilled in the art will recognize how best to implement the described functionality presented throughout this disclosure depending on the particular application and the overall design constraints imposed on the overall system. 
     In some aspects of the disclosure, at least one processor  404  may include a communication circuit  442 . The communication circuit  442  may include one or more hardware components that provide the physical structure that performs various processes related to wireless communication (e.g., signal reception and/or signal transmission) as described herein. For example, the communication circuit  442  may be configured to perform sidelink communication as described in relation to  FIGS. 7-18 . In some aspects of the disclosure, the processor  404  may also include a processing circuit  444 . The processing circuit  444  may include one or more hardware components that provide the physical structure that performs various processes related to signal processing (e.g., processing a received signal and/or processing a signal for transmission) as described herein. For example, the processing circuit  444  may be configured to perform sidelink communication as described in relation to  FIGS. 7-18 . 
     The circuitry included in the processor  404  is provided as non-limiting examples. Other means for carrying out the described functions exists and is included within various aspects of the present disclosure. In some aspects of the disclosure, the computer-readable medium  406  may store computer-executable code comprising instructions configured to perform various processes described herein. The instructions included in the computer-readable medium  406  are provided as non-limiting examples. Other instructions configured to carry out the described functions exist and are included within various aspects of the present disclosure. 
     According to various aspects of the disclosure, wireless communication may be implemented by dividing transmissions, in time, into frames, wherein each frame may be further divided into subframes or slots. These subframes or slots may be DL-centric, UL-centric, or sidelink-centric, as described below. For example,  FIG. 5  is a diagram illustrating an example of a downlink (DL)-centric slot  500  according to some aspects of the disclosure. The DL-centric slot is referred to as a DL-centric slot because a majority (or, in some examples, a substantial portion) of the slot includes DL data. In the example shown in  FIG. 5 , time is illustrated along a horizontal axis, while frequency is illustrated along a vertical axis. The time-frequency resources of the DL-centric slot  500  may be divided into a DL burst  502 , a DL traffic portion  504  and an UL burst  506 . 
     The DL burst  502  may exist in the initial or beginning portion of the DL-centric slot. The DL burst  502  may include any suitable DL information in one or more channels. In some examples, the DL burst  502  may include various scheduling information and/or control information corresponding to various portions of the DL-centric slot. In some configurations, the DL burst  502  may be a physical DL control channel (PDCCH), as indicated in  FIG. 5 . Additional description related to the PDCCH is provided further below with reference to various other drawings. The DL-centric slot may also include a DL traffic portion  504 . The DL traffic portion  504  may sometimes be referred to as the payload of the DL-centric slot. The DL traffic portion  504  may include the communication resources utilized to communicate DL user data traffic from the scheduling entity  202  (e.g., eNB) to the scheduled entity  204  (e.g., UE). In some configurations, the DL traffic portion  504  may be a physical DL shared channel (PDSCH). 
     The UL burst  506  may include any suitable UL information in one or more channels. In some examples, the UL burst  506  may include feedback information corresponding to various other portions of the DL-centric slot. For example, the UL burst  506  may include feedback information corresponding to the control portion  502  and/or DL traffic portion  504 . Non-limiting examples of feedback information may include an ACK signal, a NACK signal, a HARQ indicator, and/or various other suitable types of information. The UL burst  506  may include additional or alternative information, such as information pertaining to random access channel (RACH) procedures, scheduling requests (SRs), and various other suitable types of information. 
     As illustrated in  FIG. 5 , the end of the DL traffic portion  504  may be separated in time from the beginning of the UL burst  506 . This time separation may sometimes be referred to as a gap, a guard period, a guard interval, and/or various other suitable terms. This separation provides time for the switch-over from DL communication (e.g., reception operation by the scheduled entity  204  (e.g., UE)) to UL communication (e.g., transmission by the scheduled entity  204  (e.g., UE)). One of ordinary skill in the art will understand that the foregoing is merely one example of a DL-centric slot and alternative structures having similar features may exist without necessarily deviating from the aspects described herein. 
       FIG. 6  is a diagram showing an example of an uplink (UL)-centric slot  600  according to some aspects of the disclosure. The UL-centric slot is referred to as a UL-centric slot because a majority (or, in some examples, a substantial portion) of the slot includes UL data. In the example shown in  FIG. 6 , time is illustrated along a horizontal axis, while frequency is illustrated along a vertical axis. The time-frequency resources of the UL-centric slot  600  may be divided into a DL burst  602 , an UL traffic portion  604  and an UL burst  606 . 
     The DL burst  602  may exist in the initial or beginning portion of the UL-centric slot. The DL burst  602  in  FIG. 6  may be similar to the DL burst  502  described above with reference to  FIG. 5 . The UL-centric slot may also include an UL traffic portion  604 . The UL traffic portion  604  may sometimes be referred to as the payload of the UL-centric slot. The UL traffic portion  604  may include the communication resources utilized to communicate UL user data traffic from the scheduled entity  204  (e.g., UE) to the scheduling entity  202  (e.g., eNB). In some configurations, the UL traffic portion  604  may be a physical UL shared channel (PUSCH). As illustrated in  FIG. 6 , the end of the DL burst  602  may be separated in time from the beginning of the UL traffic portion  604 . This time, separation may sometimes be referred to as a gap, guard period, guard interval, and/or various other suitable terms. This separation provides time for the switch-over from DL communication (e.g., reception operation by the scheduling entity  202  (e.g., UE)) to UL communication (e.g., transmission by the scheduling entity  202  (e.g., UE)). 
     The UL burst  606  in  FIG. 6  may be similar to the UL burst  506  described above with reference to  FIG. 5 . The UL burst  606  may additionally or alternatively include information pertaining to channel quality indicator (CQI), sounding reference signals (SRSs), and various other suitable types of information. One of ordinary skill in the art will understand that the foregoing is merely one example of an UL-centric slot, and alternative structures having similar features may exist without necessarily deviating from the aspects described herein. 
     In some circumstances, two or more scheduled entities  204  (e.g., UEs) may communicate with each other using sidelink signals. Real-world applications of such sidelink communications may include public safety, proximity services, UE-to-network relaying, vehicle-to-vehicle (V2V) communications, Internet of Everything (IoE) communications, IoT communications, mission-critical mesh, and/or various other suitable applications. Generally, a sidelink signal may refer to a signal communicated from one scheduled entity  204  (e.g., UE 1 ) to another scheduled entity  204  (e.g., UE 2 ) without relaying that communication through the scheduling entity  202  (e.g., eNB), even though the scheduling entity  202  (e.g., eNB) may be utilized for scheduling and/or control purposes. In some examples, the sidelink signals may be communicated using licensed spectrum (unlike wireless local area networks, which typically use an unlicensed spectrum). 
     However, communication using sidelink signals may increase the relative likelihood of signal interference in certain circumstances. For example, without the aspects described in the present disclosure, interference may occur between the sidelink signals and the DL/UL control/scheduling information of nominal traffic. That is, the DL/UL control/scheduling information of nominal traffic may not be as well protected. As another example, without the aspects described in the present disclosure, interference may occur between sidelink signals originating from different scheduled entities  204  (e.g., UEs). That is, concurrently transmitted sidelink signals may collide and/or interfere with each other. Aspects of the present disclosure provide for an interference management scheme for concurrent sidelink signals and sidelink-centric subframes or slots that enable sidelink interference management. 
       FIG. 7  is a diagram illustrating an example of a sidelink-centric slot  700  according to some aspects of the present disclosure. In some configurations, this sidelink-centric slot may be utilized for broadcast communication. A broadcast communication may refer to a point-to-multipoint transmission by one scheduled entity  204  (e.g., UE 1 ) to a set of one or more scheduled entities  204  (e.g., UE 2 -UE N ). In this example, the sidelink-centric slot includes a DL burst  702 , which may include a PDCCH. In some aspects, the DL burst  702  may be similar to the DL burst  502  described in greater detail above with reference to  FIG. 5 . Additionally or alternatively, the DL burst  702  may include grant information related to the sidelink signal or sidelink communication. Non-limiting examples of grant information may include generic grant information and link-specific grant information. Link-specific grant information may refer to information that enables a specific sidelink communication to occur between two particular scheduled entities  204  (e.g., UEs). In comparison, generic grant information may refer to information that generally enables sidelink communications to occur within a particular cell, without specifying a particular sidelink communication. 
     Notably, as illustrated in  FIG. 7 , the DL burst  702  may be included in the beginning or initial portion of the sidelink-centric slot. By including the DL burst  702  in the beginning or initial portion of the sidelink-centric slot, the likelihood of interfering with the DL bursts  502 ,  602  of DL-centric and UL-centric slots of nominal traffic can be reduced or minimized. In other words, because the DL-centric slot, the UL-centric slot, and the sidelink-centric slot have their DL control information communicated during a common portion of their respective slots, the likelihood of interference between the DL control information and the sidelink signals can be reduced or minimized That is, the DL bursts  502 ,  602  of DL-centric and UL-centric slots (of nominal traffic) are relatively better protected. 
     The sidelink-centric slot  700  may also include a source transmit signal (STS)  704  portion (formerly referred to as, or similar to a, request-to-send (RTS) portion). The STS  704  portion may refer to a portion of the slot during which one scheduled entity  204  (e.g., a UE utilizing a sidelink signal) communicates a request signal (i.e., an STS) indicating a requested duration of time to keep a sidelink channel available for a sidelink signal. One of ordinary skill in the art will understand that the STS may include various additional or alternative information without necessarily deviating from the scope of the present disclosure. In some configurations, the STS may include a group destination identifier (ID). The group destination ID may correspond to a group of devices that are intended to receive the STS. In some configurations, the STS may indicate a duration of the sidelink transmission, and/or may include a reference signal to enable channel estimation and RX-yielding (described below), a modulation and coding scheme (MCS) indicator, and/or various other information. In some examples, the STS reference signal may be transmitted at a higher (e.g., boosted) power level to provide additional protection of the broadcast. Further, the STS MCS indicator may be utilized to inform the receiving device of the MCS utilized for transmissions in the sidelink data portion  706 . Here, the reference signal may take any suitable form or structure on the channel that may be useful for interference management (e.g., by creating a predictable amount of interference) and channel management at the receiver. In some configurations, the STS (or, in other examples, the DRS) may include a release flag, configured to explicitly signal that the transmitting device is releasing sidelink resources that may have previously been requested by the transmitting device, or in other words, sending an explicit release signal to indicate that a sidelink device is releasing a sidelink resource. Therefore, the release flag may be set in explicit sidelink signaling (e.g., STS/DRS) to indicate that a sidelink device is releasing a sidelink resource so that other users, which may have been backing off, can get back into trying to access or use the sidelink resources that were previously unavailable. 
     For the sake of completeness, the following information is provided regarding RX-yielding. Assume that two sidelinks exist. Sidelink 1  is between UE A  and UE B , and Sidelink 2  is between UE C  and UE D . Assume also that Sidelink 1  has a higher priority than Sidelink 2 . If UE A  and UE C  concurrently transmit STS, UE D  will refrain from transmitting a DRS, because Sidelink 1  has a higher priority than Sidelink 2 . Accordingly, the relatively lower priority sidelink (Sidelink 2 ) yields communication of the DRS under these circumstances. 
     A first scheduled entity  204  (e.g., UE 1 ) may transmit an STS to one or more other scheduled entities  204  (e.g., UE 2 , UE 3 ) to request that the other scheduled entities  204  (e.g., UE 2 , UE 3 ) refrain from using the sidelink channel for the requested duration of time, thereby leaving the sidelink channel available for first scheduled entity  204  (e.g., UE 1 ). By transmitting the STS, the first scheduled entity  204  (e.g., UE 1 ) can effectively reserve the sidelink channel for a sidelink signal. This enables distributed scheduling and management of interference that might otherwise occur from another sidelink communication from other scheduled entities  204  (e.g., UE 2 , UE 3 ). Put another way, because the other scheduled entities  204  (e.g., UE 2 , UE 3 ) are informed that the first scheduled entity  204  (e.g., UE 1 ) will be transmitting for the requested period of time, the likelihood of interference between sidelink signals is reduced. 
     The sidelink-centric slot  700  may also include a sidelink traffic portion  706 . The sidelink traffic portion  706  may sometimes be referred to as the payload or sidelink-burst of the sidelink-centric slot. In an example where the sidelink-centric slot is utilized for broadcast communications, the sidelink traffic portion  706  may carry a physical sidelink broadcast channel (PSBCH) (formerly a physical sidelink shared channel (PSSCH)), as indicated in  FIG. 7 . The sidelink traffic portion  706  may include the communication resources utilized to communicate sidelink user data traffic from one scheduled entity  204  (e.g., UE 1 ) to one or more other scheduled entities  204  (e.g., UE 2 , UE 3 ). 
     According to a further aspect of the disclosure, a broadcast sidelink-centric slot may take on certain characteristics based on whether or not the broadcast is separated from other sidelink devices that utilize unicast sidelink-centric slots as described above. Here, a broadcast sidelink-centric slot utilized in the absence of unicast sidelink-centric slot transmissions may be referred to as an orthogonalized broadcast, while a broadcast sidelink-centric slot utilized in the presence of unicast sidelink-centric slot transmissions may be referred to as an in-band broadcast. 
     The sidelink traffic portion  706  may be configured utilizing a suitable MCS selected according to channel conditions. In one example, the receiving device may select an MCS based on a measurement of a receive power of a reference signal in the STS  704  portion, and a measurement of interference. For example, in low receive power and/or high interference scenarios, the receiving device may select a more robust MCS, e.g., utilizing a lower modulation order and/or a lower coding rate. 
     The sidelink-centric slot  700  may also include an UL burst  708 . In some aspects, the UL burst  708  may be similar to the UL burst  506 ,  606  described above with reference to  FIGS. 5-6 . Notably, as illustrated in  FIG. 7 , the UL burst  708  may be included in the end portion of the sidelink-centric slot  700 . By including the UL burst  708  in the end portion of the sidelink-centric slot, the likelihood of interfering with the UL bursts  506 ,  606  of DL-centric and UL-centric slots of nominal traffic is minimized or reduced. In other words, because the DL-centric slot, the UL-centric slot, and the sidelink-centric slot have their UL bursts  506 ,  606 ,  708  communicated during a similar portion of their respective slot, the likelihood of interference between those UL bursts  506 ,  606 ,  708  is minimized or reduced. That is, the UL bursts  506 ,  606  of DL-centric and UL-centric slots (of nominal traffic) are relatively better protected. 
       FIG. 8  is a diagram illustrating an example of multiple concurrent sidelink-centric slots  800  according to some aspects of the present disclosure. In some configurations, the sidelink-centric slots may be utilized for broadcast communication. Although the example illustrated in  FIG. 8  shows three slots (e.g., SLOT N , SLOT N+1 , SLOT N+2 ), one of ordinary skill in the art will understand that any plural number of slots may be included without deviating from the scope of the present disclosure. The first slot (e.g., SLOT N ) may include a DL burst  802  (e.g., PDCCH, as described in greater detail above) and an STS portion  804  (as also described in greater detail above). The STS portion  804  may indicate a duration that extends across more than one slot (e.g., SLOT N , SLOT N+1 , SLOT N+2 ). In other words, the STS may indicate a requested duration of time to keep the sidelink channel available for sidelink signals, and that requested duration may extend until the end of the last slot (e.g., SLOT N+2 ) of a plurality of slots (e.g., SLOT N , SLOT N+1 , SLOT N+2 ). Therefore, although the plurality of slots (e.g., SLOT N , SLOT N+1 , SLOT N+2 ) each include a sidelink traffic portion  806 ,  812 ,  818 , not every slot requires the STS portion  804 . By not including the STS portion  804  in every slot of the plurality of slots (e.g., SLOT N , SLOT N+1 , SLOT N+2 ), the overall amount of overhead is relatively lower than it would otherwise be (e.g., if the STS portion  804  was included in every slot). By reducing overhead, relatively more of the slots (e.g., SLOT N+1 , SLOT N+2 ) lacking the STS portion  804  can be utilized for communication of the sidelink traffic portion  812 ,  818 , which thereby increases relative throughput. 
     Within the first slot (e.g., SLOT N ), the STS portion  804  may be followed by a sidelink traffic portion  806  (which is described in greater detail above with reference to the sidelink traffic portion  706  in  FIG. 7 ). The sidelink traffic portion  806  may be followed by the UL burst  808  (which is described in greater detail above with reference to the UL burst  708  in  FIG. 7 ). In the example illustrated in  FIG. 8 , every slot (e.g., SLOT N+1 , SLOT N+2 ) following the first slot (e.g., SLOT N ) includes a DL burst  810 ,  816  at an initial/beginning portion of each slot and an UL burst  814 ,  820  at the end portion of each slot. By providing the DL burst  810 ,  816  at the initial/beginning of each slot and providing the UL burst  814 ,  820  at the end portion of each slot, the sidelink-centric slots have a structure that minimizes the likelihood of interference with DL/UL control/scheduling information of nominal traffic (as described in greater detail above). 
       FIG. 9  is a diagram illustrating another example of a sidelink-centric slot  900  according to some aspects of the present disclosure. In some configurations, this sidelink-centric slot, or a slot having similar structure, may be utilized for a unicast communication. A unicast communication may refer to a point-to-point transmission by a scheduled entity  204  (e.g., UE 1 ) to a particular scheduled entity  204  (e.g., UE 2 ). 
     In each of the sidelink-centric slots that follow, as described below, for a given device, certain fields or portions of the slot may correspond to transmissions from that device or reception at that device, depending on whether that given device is transmitting sidelink traffic or receiving sidelink traffic. As illustrated in each of  FIGS. 9-13 , a time gap (e.g., guard interval, guard period, etc.) Between adjacent data portions, if any, may enable a device to transition from a listening/receiving state (e.g., during DSS  904  for a non-primary device) to a transmitting state (e.g., during STS  906  for a non-primary device); and/or to transition from a transmitting state (e.g., during STS  906  for a non-primary device) to a listening/receiving state (e.g., during DRS  908  for either a primary or non-primary transmitting device). The duration of such a time gap or guard interval may take any suitable value, and it should be understood that the illustrations in  FIGS. 9-14  are not to scale with respect to time. Many such time gaps are shown in the various illustrations to represent some aspects of particular embodiments, but it should be understood that the illustrated time gaps may be wider or narrower than they appear, and in some examples, an illustrated time gap may not be utilized, while in other examples, the lack of a time gap might be replaced with a suitable time gap between regions of a slot. In some aspects of the disclosure, a particular slot may be structured with time gaps corresponding to TX-RX transitions as well as RX-TX transitions, in order that the same slot structure may accommodate the operation of a given device both when that device is transmitting sidelink traffic, and when that device is receiving sidelink traffic. 
     In the example illustrated in  FIG. 9 , the sidelink-centric slot includes a DL burst  902 , which may include a physical downlink control channel (PDCCH). In some aspects, the DL burst  902  may be configured the same as or similar to the DL burst  502  (e.g., PDCCH) described in greater detail above with reference to  FIG. 5 . Additionally or alternatively, the DL burst  902  may include grant information related to the sidelink signal or sidelink communication. Non-limiting examples of grant information may include generic grant information and link-specific grant information. Link-specific grant information may refer to information that enables a specific sidelink communication to occur between two particular scheduled entities  204  (e.g., UEs). In comparison, generic grant information may refer to information that generally enables sidelink communications to occur within a particular cell, without specifying a particular sidelink communication. 
     Notably, as illustrated in  FIG. 9 , the DL burst  902  may be included in the beginning or initial portion of the sidelink-centric slot  900 . By including the DL burst  902  in the beginning or initial portion of the sidelink-centric slot  900 , the likelihood of interfering with the DL bursts  502 ,  602  of DL-centric and UL-centric slots of nominal traffic is minimized In other words, because the DL-centric slot  500 , the UL-centric slot  600 , and the sidelink-centric slot  900  have their DL control information communicated during a common portion of their respective slots, the likelihood of interference between the DL control information and the sidelink signals is minimized That is, the DL bursts  502 ,  602  of DL-centric and UL-centric slots (of nominal traffic) are relatively better protected. 
     The sidelink-centric slot  900  may further include a primary request signal such as a direction selection signal (DSS)  904 , and a secondary request signal such as a source transmit signal (STS)  906 . In various examples, the content of the DSS and the STS may take different formats. As one example, the DSS  904  may be utilized for direction selection and the STS  906  may be utilized as a request signal. Here, direction selection refers to the selection whether a primary sidelink device transmits a request signal in the STS, or whether a primary sidelink device receives a request signal (i.e., a non-primary or secondary sidelink device transmits a request signal in the STS). In this example, the DSS may include a destination ID (e.g., corresponding to a non-primary or secondary sidelink device) and a direction indication. In this manner, a listening sidelink device that receives the DSS transmission and is not the device corresponding to the destination ID need not necessarily be active and monitoring for the STS transmission. In this example, the STS may include an indication of a requested duration of time to reserve a sidelink channel for sidelink data. Accordingly, with the STS/DSS portions of the sidelink-centric slot  900 , a request for reservation of the sidelink channel in a desired direction between a primary and a non-primary sidelink device may be established. 
     In another example, content of the DSS  904  and the STS  906  may be substantially similar to one another, although the DSS  904  may be utilized by a primary sidelink device and the STS  906  may be utilized by a secondary sidelink device. The DSS and/or STS may be utilized by a scheduled entity  204  (e.g., UE) as a request signal to indicate a requested duration of time to keep a sidelink channel available for a sidelink signal. One of ordinary skill in the art will understand that the DSS and/or STS may include various additional or alternative information without necessarily deviating from the scope of the present disclosure. In some configurations, the DSS and/or STS may include a destination identifier (ID). The destination ID may correspond to a specific apparatus intended to receive the STS/DSS (e.g., UE 2 ). In some configurations, the DSS and/or STS may indicate a duration of the sidelink transmission, and/or may include a reference signal to enable channel estimation and RX-yielding, a modulation and coding scheme (MCS) indicator, and/or various other information. Here, the MCS indicator may be utilized to inform the receiving device of the MCS utilized for transmissions in the sidelink traffic portion. 
     A primary device may transmit a primary request signal (e.g., a DSS) during a primary request portion of a slot (e.g., DSS  904 ), and a non-primary device (e.g., a secondary device) may transmit a secondary request signal (e.g., an STS) during a secondary request portion of the slot (e.g., STS  906  portion). A primary device may refer to a device (e.g., a UE or scheduled entity  204 ) that has priority access to the sidelink channel During an association phase, one device may be selected as the primary device and another device may be selected as the non-primary (e.g., secondary) device. In some configurations, the primary device may be a relay device that relays a signal from a non-relay device to another device, such as a scheduling entity  202  (e.g., base station). The relay device may experience relatively less path loss (when communicating with the scheduling entity  202  (e.g., base station)) relative to the path loss experienced by the non-relay device. 
     During the DSS  904  portion, the primary device transmits a DSS, and the non-primary device listens for the DSS from a primary device. On the one hand, if the non-primary device detects a DSS during the DSS  904  portion, then the non-primary device will not transmit an STS during the STS  906  portion. On the other hand, if the non-primary device does not detect a DSS during the DSS  904  portion, then the non-primary device may transmit an STS during the STS  906  portion. 
     If the sidelink channel is available for the requested duration of time, an apparatus identified or addressed by the destination ID in the STS/DSS, which receives the STS/DSS, may communicate a confirmation signal, such as a destination receive signal (DRS), during the DRS  908  portion. The DRS may indicate availability of the sidelink channel for the requested duration of time. The DRS may additionally or alternatively include other information, such as a source ID, a duration of the transmission, a signal to interference plus noise ratio (SINR) (e.g., of the received reference signal from the source device), a reference signal to enable TX-yielding, CQI information, and/or various other suitable types of information. The exchange of STS/DSS and DRS enable the scheduled entities  204  (e.g., UEs) performing the sidelink communications to negotiate the availability of the sidelink channel prior to the communication of the sidelink signal, thereby minimizing the likelihood of interfering sidelink signals. In other words, without the STS/DSS and DRS, two or more scheduled entities  204  (e.g., UEs) might concurrently transmit sidelink signals using the same resources of the sidelink traffic portion  910 , thereby causing a collision and resulting in avoidable retransmissions. 
     The sidelink-centric slot may also include a sidelink traffic portion  910 . The sidelink traffic portion  910  may sometimes be referred to as the payload or sidelink-burst of the sidelink-centric slot. In an example where the sidelink-centric slot is utilized for unicast transmissions, the sidelink traffic portion  910  may carry a physical sidelink shared channel (PSSCH). The sidelink traffic portion  910  may include the communication resources utilized to communicate sidelink user data traffic from one scheduled entity  204  (e.g., UE 1 ) to a second scheduled entity  204  (e.g., UE 2 ). In some configurations, the MCS of the sidelink signal communicated in the sidelink traffic portion  910  may be selected based on the CQI feedback included in the DRS  908 . 
     The sidelink-centric slot may also include a sidelink acknowledgment portion  912 . In some aspects, the sidelink acknowledgment portion  912  may carry a physical sidelink HARQ indicator channel (PSHICH). After communicating the sidelink signal in the sidelink traffic portion  910 , acknowledgment information may be communicated between the scheduled entities  204  (e.g., UEs) utilizing the sidelink acknowledgment portion  912 . Non-limiting examples of such acknowledgment information may include an ACK signal, a NACK signal, a HARQ indicator, and/or various other suitable types of acknowledgment information. For example, after receiving and successfully decoding a sidelink signal from UE 1  in the sidelink traffic portion  910 , UE 2  may transmit an ACK signal to the UE 1  in the sidelink acknowledgment portion  912  of the sidelink-centric slot. 
     The sidelink-centric slot may also include an UL burst  914 . In some aspects, the UL burst  914  may be configured the same as or similar to the UL burst  506 ,  606  described above with reference to  FIGS. 5-6 . Notably, as illustrated in the example of  FIG. 9 , the UL burst  914  may be included in the end portion of the sidelink-centric slot. By including the UL burst  914  in the end portion of the sidelink-centric slot, the likelihood of interfering with the UL burst  506 ,  606  of DL-centric and UL-centric slots of nominal traffic is minimized In other words, because the DL-centric slot, the UL-centric slot, and the sidelink-centric slot have their UL burst  506 ,  606 ,  914  communicated during the same or similar portion of their respective slot, the likelihood of interference between those UL bursts  506 ,  606 ,  914  is reduced. That is, the UL bursts  506 ,  606  of DL-centric and UL-centric slots (of nominal traffic) are relatively better protected. 
       FIGS. 10-11 , described below, illustrate multiple concurrent sidelink-centric slots according to some aspects of the disclosure. As with the example described above in relation to  FIG. 9 , in some configurations, the concurrent sidelink-centric slots in  FIGS. 10 and 11  may be utilized for unicast communication. Although the examples illustrated in  FIGS. 10 and 11  show three slots (e.g., SLOT N , SLOT N+1 , SLOT N+2 ), one of ordinary skill in the art will understand that any plural number of concurrent sidelink-centric slots may be included as described herein without deviating from the scope of the present disclosure. 
     Referring now specifically to  FIG. 10 , a diagram illustrates an example of multiple concurrent sidelink-centric slots  1000  according to an aspect of the present disclosure. The first slot (e.g., SLOT N ) may include the DL burst  1002  (e.g., PDCCH, as described in greater detail above), DSS  1004 , STS  1006 , and DRS  1008  (as also described in greater detail above). In this example, the request signal communicated during DSS  1004  and/or STS  1006  may indicate a duration that extends across the plurality of slots (e.g., SLOT N , SLOT N+1 , SLOT N+2 ). In other words, the request signal may indicate a requested duration of time to keep the sidelink channel available for sidelink signals, and that requested duration may extend until the end of the last slot (e.g., SLOT N+2 ) of the plurality of slots (e.g., SLOT N , SLOT N+1 , SLOT N+2 ). If the sidelink channel is available for that requested duration of time, then the confirmation signal (e.g., DRS) may be communicated in the DRS  1008  portion (as described in greater detail above). 
     Although the plurality of slots (e.g., SLOT N , SLOT N+1 , SLOT N+2 ) each include a sidelink traffic portion  1010 ,  1016 ,  1022 , not every slot necessarily requires DSS  1004  and/or STS  1006 . By not including DSS  1004  and/or STS  1006  in every slot of the plurality of slots (e.g., SLOT N , SLOT N+1 , SLOT N+2 ), the overall amount of overhead is relatively lower than it would otherwise be (e.g., if DSS  1004  and/or STS  1006  were included in every slot). By reducing overhead, relatively more of the slots (e.g., SLOT N+1 , SLOT N+2 ) lacking DSS  1004  and/or STS  1006  can be utilized for communication of the sidelink traffic  1016 ,  1022 , which thereby increases relative throughput. 
     Within the first slot (e.g., SLOT N ), DSS  1004 , STS  1006 , and DRS  1008  may be followed by a first sidelink traffic portion  1010  (which is described in greater detail above with reference to the sidelink traffic portion  910  in  FIG. 9 ). The sidelink traffic portions  1010 ,  1016 , and  1022  may each be followed by respective UL bursts  1012 ,  1018 , and  1026  (which are described in greater detail above with reference to the UL burst  914  in  FIG. 9 ). In the example illustrated in  FIG. 10 , every slot (e.g., SLOT N+1 , SLOT N+2 ) following the first slot (e.g., SLOT N ) includes a DL burst  1014 ,  1020  at an initial/beginning portion of each slot and an UL burst  1018 ,  1026  at the end portion of each slot. By providing the DL burst  1014 ,  1020  at the initial/beginning of each slot and providing the UL burst  1018 ,  1026  at the end portion of each slot, the sidelink-centric slots have a structure that minimizes the likelihood of interference with DL/UL control/scheduling information of nominal traffic (as described in greater detail above). 
     In the example illustrated in  FIG. 10 , the sidelink-centric slots  1000  include a single sidelink acknowledgment portion  1024  in a last/final slot (e.g., SLOT N+2 ) of the plurality of slots (e.g., SLOT N , SLOT N+1 , SLOT N+2 ). The acknowledgment information communicated in the sidelink acknowledgment portion  1024  in the last/final slot (e.g., SLOT N+2 ) may correspond to the sidelink signals included in one or more (e.g., all) preceding sidelink traffic portions  1010 ,  1016 ,  1022 . For example, the sidelink acknowledgment portion  1024  may include a HARQ identifier corresponding to sidelink signals communicated throughout the sidelink traffic portions  1010 ,  1016 ,  1022  of the plurality of slots (e.g., SLOT N , SLOT N+1 , SLOT N+2 ). Because the sidelink acknowledgment portion  1024  is not included in every slot (e.g., SLOT N , SLOT N+1 ), the overall amount of overhead is relatively lower than it would otherwise be (e.g., if a sidelink acknowledgment portion were included in every slot). By reducing overhead, relatively more of the slots (e.g., SLOT N , SLOT N+1 ) lacking the sidelink acknowledgment portion  1024  can be utilized for communication of sidelink user data traffic, which thereby increases relative throughput. However, one of ordinary skill in the art will readily understand that the example illustrated in  FIG. 10  is non-limiting and alternative configurations may exist without necessarily deviating from the scope of the present disclosure. 
       FIG. 11  is a diagram illustrating one example of such an alternative configuration of multiple concurrent sidelink-centric slots  1100 . Various aspects illustrated in  FIG. 11  (e.g., DL bursts  1102 ,  1116 ,  1124 ; DSS  1104 ; STS  1106 ; DRS  1108 ; and UL bursts  1114 ,  1122 ,  1130 ) are described above with reference to  FIG. 7  and therefore will not be repeated here to avoid redundancy. An aspect in which the example illustrated in  FIG. 11  may differ from the example illustrated in  FIG. 10  is that the example in  FIG. 11  includes a sidelink acknowledgment portion  1112 ,  1120 ,  1128  in every slot of the plurality of slots (e.g., SLOT N , SLOT N+1 , SLOT N+2 ). For example, each sidelink acknowledgment portion  1112 ,  1120 , and  1128  may respectively communicate acknowledgment information corresponding to a sidelink signal included in the sidelink traffic portion  1110 ,  1118 , and  1126  in its slot. By receiving acknowledgment information corresponding to the sidelink signal in that particular slot, the scheduled entity  204  (e.g., UE) may obtain relatively better specificity regarding the communication success of each sidelink signal. For example, if only one sidelink signal in a single sidelink traffic portion (e.g., sidelink traffic portion  1110 ) is not successfully communicated, retransmission can be limited to only the affected sidelink traffic portion (e.g., sidelink traffic portion  1110 ) without the burden of retransmitting unaffected sidelink traffic portions (e.g., other sidelink traffic portions  1118 ,  1126 ). 
     In next-generation (e.g., 5G) networks, the slot duration may be shorter to support lower latency. However, the STS and DRS within the sidelink-centric slot  900  shown in  FIG. 9  and/or the sidelink-centric slots shown in  FIGS. 10 and 11  may contribute significant overhead, which may increase the duration of the sidelink-centric slot beyond that which 5G networks support. 
     Therefore, in accordance with various aspects of the disclosure, the STS and/or DRS overhead may be reduced using a single-tone signal instead of a multiple-tone signal. As used herein, the term “single-tone signal” refers to a signal generated without digital coding, while the term “multiple-tone signal” refers to a signal generated using digital coding. In addition, as used herein, the term “single-tone signal” refers to a signal that achieves signaling of information through tone identifiers (IDs) (e.g., specific frequencies) and/or signal power levels. For example, single-tone signaling of the STS and/or DRS over the sidelink may utilize tone IDs negotiated between the transmitting and receiving sidelink devices and/or transmit power levels to convey STS and/or DRS information. 
     In some examples, a single-tone signal may include an analog signal. As used herein, the term “analog signaling” or “analog signal” refers to analog modulation (e.g., amplitude modulation (AM), frequency modulation (FM), phase modulation (PM), double sideband AM, single sideband AM, etc.) of a carrier signal at a transmitting device to transmit information from the transmitting device to a receiving device over the sidelink. However, the term “single-tone signal” is not limited to analog signals, and may include any suitable signal generated without digital coding that utilizes tone identifiers and/or power levels to convey information. In some examples, a multiple-tone signal may include a digital signal. As used herein, the term “digital signaling” or “digital signal” refers to digital modulation (e.g., BPSK, QPSK, QAM, etc.) of a carrier signal at a transmitting device to transmit information from the transmitting device to a receiving device over the sidelink. However, the term “multiple-tone signal” is not limited to digital signals, and may include any suitable digitally coded signal. 
     In some instances, single-tone signaling may not provide adequate reliable signaling. For example, the DRS may require multiple-tone signaling to adequately transmit the CQI. Therefore, various aspects of the disclosure may further provide for a combination of single-tone and multiple-tone signaling in the STS and DRS portions of a sidelink slot. 
       FIG. 12  is a diagram illustrating one example of a configuration of a sidelink-centric slot  1200  utilizing a combination of single-tone and multiple-tone signaling. Various aspects illustrated in  FIG. 12  (e.g., DL burst  1202 , sidelink traffic portion  1210 , sidelink acknowledgment portion  1212  and UL burst  1214 ) are described above with reference to  FIG. 9  and therefore will not be repeated here to avoid redundancy. 
     In the example shown in  FIG. 12 , the primary request signal (e.g., the DSS  1204 ) may be a single-tone signal, while the secondary request signal (e.g., STS  1206 ) and the confirmation signal (e.g., DRS  1208 ) may be multiple-tone signals. As described above, the DSS  1204  is utilized to indicate link direction of the sidelink traffic portion  1210  (e.g., from the primary device to the secondary device when the primary device transmits the DSS  1204 ). Therefore, the DSS  1204  may easily be implemented using single-tone signaling. 
     To provide sufficient reliability for the STS  1206 , which may carry the destination ID, transmission duration and other information (e.g., reference signal, MCS indicator, etc.), the STS  1206  may be a multiple-tone (e.g., digital) signal. Similarly, the DRS  1208  may be a multiple-tone (e.g., digital) signal to provide sufficient reliability for channel state information (e.g., CQI), along with other information, such as the source ID, the duration of the transmission, SINR, the reference signal to enable TX-yielding, ,and/or various other suitable types of information. 
       FIG. 13  is a diagram illustrating another example of a configuration of a sidelink-centric slot  1300  utilizing a combination of single-tone and multiple-tone signaling. Various aspects illustrated in  FIG. 13  (e.g., DL burst  1302 , sidelink traffic portion  1310 , sidelink acknowledgment portion  1312  and UL burst  1314 ) are described above with reference to  FIG. 9  and therefore will not be repeated here to avoid redundancy. 
     In the example shown in  FIG. 13 , the secondary request signal (e.g., STS  1306 ) is a single-tone signal, while the confirmation signal (e.g., DRS  1308 ) is a multiple-tone signal. In this example, the primary request signal (e.g., DSS  1304 ) may be either a single-tone signal or a multiple-tone signal. In some examples, the DSS  1304  may be a multiple-tone signal to include a reference signal that enables channel estimation at the receiving device. 
     To significantly reduce overhead, both the primary request signal (e.g., DSS  1304 ) and the secondary request signal (e.g., STS  1306 ) may be single-tone signals, while the confirmation signal (e.g., DRS  1308 ) may be a multiple-tone signal. In this example, the destination ID may include a tone ID (e.g., frequency) negotiated between the primary device and the secondary device upon establishment of the sidelink. For example, a peer discovery mechanism may be used by an initiating device to discover the presence of other devices in a neighborhood or area (e.g., within a radial distance from the location of the initiating device). Once another device of interest is discovered, the initiating device may page the device of interest to associate with the other device and establish a sidelink between the two devices. As part of the association, respective tone IDs may be selected for each device to enable single-tone signaling therebetween. In some examples, the tone IDs may be selected by the initiating device or primary device. In other examples, the tone IDs may be negotiated between the devices. The tone ID of the transmitting device may further be utilized to generate and transmit the DSS  1304 . 
     In some examples, to further minimize the overhead of the STS  1306 , the duration of sidelink transmissions may be fixed between the primary and secondary device. Therefore, the single-tone STS  1306  may not need to include a separate requested duration of time. Instead, the requested duration of time may be known to the receiving device, such that upon receiving the single-tone STS  1306 , the receiving device has a-priori knowledge of the associated requested duration of time. The fixed duration of time may be selected during the association stage or may be provided to the devices by the network (e.g., scheduling entity). For example, the fixed duration of time associated with the single-tone STS  1306  may be included within the PDCCH  1302  or another control message transmitted by the scheduling entity. 
       FIG. 14  is a diagram illustrating another example of a configuration of a sidelink-centric slot  1400  utilizing a combination of single-tone and multiple-tone signaling. Various aspects illustrated in  FIG. 14  (e.g., DL burst  1402 , sidelink traffic portion  1410 , acknowledgment portion  1412  and UL burst  1414 ) are described above with reference to  FIG. 9  and therefore will not be repeated here to avoid redundancy. 
     In the example shown in  FIG. 14 , the secondary request signal (e.g., STS  1406 ) is a multiple-tone signal to enable reliable transmission of the destination ID and/or duration information, while the confirmation signal (e.g., DRS  1408 ) is a single-tone signal. In this example, the primary request signal (e.g., DSS  1404 ) may be either a single-tone signal or a multiple-tone signal. In some examples, the sidelink signal transmit power and MCS may be fixed between the devices, thus obviating the need for CQI in the DRS  1408 . The fixed transmit power and MCS may be selected during the association stage or may be provided to the devices by the network (e.g., scheduling entity). Utilizing a fixed transmit power and MCS may still provide sufficient reliability of the sidelink signal in some scenarios, such as low-payload scenarios (e.g., IoE). 
     In various aspects of the disclosure, the transmit power of the single-tone DRS  1408  may be selected to control dimensions of a protection zone around the receiving device, thus managing interference for the sidelink signal. As used herein, the term “protection zone” is defined as an area within which the DRS  1408  may be received by other devices. Since the DRS  1408  enables Tx-yielding, any other devices within the protection zone that receive the DRS  1408  and have a lower priority may refrain from transmitting potentially interfering sidelink signals for the indicated duration of time. Thus, the single-tone DRS  1408  may essentially operate as a power backoff instruction to other devices. In some examples, the receiving device may increase the transmit power of the DRS  1408  to increase the protection zone and reduce interference. 
     Although the controllable DRS transmit power for interference management is described above in connection with a single-tone DRS  1408 , it should be understood that the DRS power setting may also be controllable in multiple-tone implementations of the STS and DRS to facilitate power backoff and interference management. In addition to power backoff, such a multiple-tone DRS  1408  may also include other link interference management information, such as the measured SINR of the link, channel quality information, and a reference signal to support Tx-yielding, as described above. 
       FIG. 15  is a flow chart illustrating an exemplary process  1500  for single-tone and multiple-tone sidelink signaling in accordance with some aspects of the present disclosure. As described below, some or all illustrated features may be omitted in a particular implementation within the scope of the present disclosure, and some illustrated features may not be required for implementation of all embodiments. In the following description, a sidelink signal transmission is discussed with reference to a transmitting sidelink device and a receiving sidelink device. It will be understood that either device may be the user equipment  126  and/or  128  illustrated in  FIG. 1 ; the scheduling entity  202  illustrated in  FIGS. 2 and 3 ; and/or the scheduled entity  204  illustrated in  FIGS. 2 and 4 . In some examples, the process  1500  may be carried out by any suitable apparatus or means for carrying out the functions or algorithm described below. 
     At block  1502 , the transmitting sidelink device may prepare to transmit a request signal (RS) to a receiving sidelink device. At block  1504 , the transmitting sidelink device may determine whether the request signal (e.g., one or both of the DSS and/or STS) should be a single-tone signal or a multiple-tone signal. In addition, the transmitting sidelink device may determine whether a confirmation signal (CS) (e.g., the DRS) should be a single-tone signal or a multiple-tone signal. In some examples, the transmitting and receiving sidelink devices may negotiate whether the request signal (e.g., one or both of the DSS and/or STS) and/or the confirmation signal may be single-tone or multiple-tone signals during the initial association therebetween. In other examples, the network (e.g., scheduling entity) may indicate whether the request signal and confirmation signal should be single-tone or multiple-tone signals. 
     For example, if the STS and DRS signals each require digital signaling to provide sufficient reliability of the information transmitted in the STS and DRS signals, the DSS signal may be selected to be a single-tone signal. However, if the duration of sidelink transmissions is fixed, and therefore, known by both the transmitting and receiving sidelink devices, both the DSS and STS may be selected to be single-tone signals. The determination of whether the STS should be a single-tone signal or a multiple-tone signal may also be based upon whether the DRS should be single-tone or multiple-tone. For example, if the sidelink signal transmit power and MCS are fixed between the transmitting and receiving sidelink devices, the DRS may be selected to be a single-tone signal. In some examples, if the DRS is selected to be a single-tone signal, at least the STS may be selected to be a multiple-tone signal to provide for reliable destination ID information and Rx-yielding for other links. For example, the processing circuit  444  shown and described above in reference to  FIG. 4  may determine whether the request signal(s) and confirmation signal should be single-tone or multiple-tone. 
     If the request signal includes a single-tone signal (e.g., at least one of the DSS and/or STS is a single-tone signal) and the confirmation signal is a multiple-tone signal (Y branch of  1504 ), the process proceeds to block  1506 , where the transmitting sidelink device may generate the single-tone request signal. In some examples, when the STS is a single-tone signal, the transmitting and receiving sidelink devices may each be identified using a tone ID, and the transmitting sidelink device may generate the STS using the tone ID of the receiving sidelink device. For example, the processing circuit  444  shown and described above in reference to  FIG. 4  may generate the single-tone request signal. 
     At block  1508 , the transmitting sidelink device may then transmit the single-tone request signal to the receiving sidelink device. In some examples, the transmitting sidelink device transmits both the DSS and STS, at least one of which is a single-tone signal. In other examples, the transmitting sidelink device transmits a single-tone STS, while another sidelink device transmits a single-tone DSS or multiple-tone DSS when the transmitting sidelink device is not the primary sidelink device. For example, the communication circuit  442  and transceiver  410  shown and described above in reference to  FIG. 4  may transmit the single-tone request signal. 
     At block  1510 , the transmitting sidelink device may then receive a multiple-tone confirmation signal from the receiving sidelink device. In some examples, the multiple-tone confirmation signal may include a source ID of the transmitting sidelink device and various link interference management information, such as a transmit power setting to control power backoff (e.g., within a protection zone), the measured SINR of the link, channel quality information (e.g., CQI), and a reference signal to support Tx-yielding. For example, the communication circuit  442  and transceiver  410  shown and described above in reference to  FIG. 4  may receive the multiple-tone confirmation signal. 
     However, if the request signal is not a single-tone signal (e.g., at least the STS) and the confirmation signal (e.g., DRS) is not a multiple-tone signal (N branch of  1504 ), the process proceeds to block  1512 , where the transmitting sidelink device generates a multiple-tone request signal (e.g., at least a multiple-tone STS). In some examples, the STS may be a multiple-tone signal to provide reliable destination information and/or transmission duration information. For example, the processing circuit  444  shown and described above in reference to  FIG. 4  may generate the multiple-tone request signal. 
     At block  1514 , the transmitting sidelink device may then transmit the multiple-tone request signal to the receiving sidelink device. In some examples, the transmitting sidelink device transmits both the DSS and STS, where at least the STS is a multiple-tone signal. In other examples, the transmitting sidelink device transmits a multiple-tone STS, while another sidelink device transmits a single-tone DSS or multiple-tone DSS when the transmitting sidelink device is not the primary sidelink device. For example, the communication circuit  442  and transceiver  410  shown and described above in reference to  FIG. 4  may transmit the multiple-tone request signal. 
     At block  1516 , the transmitting sidelink device may then receive a single-tone confirmation signal from the receiving sidelink device. In some examples, as described above, the confirmation signal may be single-tone when the sidelink signal transmit power and MCS are fixed between the transmitting and receiving sidelink devices. The transmit power of the single-tone confirmation signal may further be set to control dimensions of the protection zone around the receiving sidelink device in order to manage interference of a subsequently transmitted sidelink signal from the transmitting sidelink device to the receiving sidelink device. For example, the communication circuit  442  and transceiver  410  shown and described above in reference to  FIG. 4  may receive the single-tone confirmation signal. 
       FIG. 16  is a flow chart illustrating another exemplary process  1600  for single-tone and multiple-tone sidelink signaling in accordance with some aspects of the present disclosure. As described below, some or all illustrated features may be omitted in a particular implementation within the scope of the present disclosure, and some illustrated features may not be required for implementation of all embodiments. In the following description, a sidelink signal transmission is discussed with reference to a transmitting sidelink device and a receiving sidelink device. It will be understood that either device may be the user equipment  126  and/or  128  illustrated in  FIG. 1 ; the scheduling entity  202  illustrated in  FIGS. 2 and 3 ; and/or the scheduled entity  204  illustrated in  FIGS. 2 and 4 . In some examples, the process  1600  may be carried out by any suitable apparatus or means for carrying out the functions or algorithm described below. 
     At block  1602 , the transmitting sidelink device may prepare to transmit a primary request signal (PRS), such as a DSS, to a receiving sidelink device. At block  1604 , the transmitting sidelink device may determine whether the DSS should be a single-tone signal or a multiple-tone signal. For example, the processing circuit  444  shown and described above in reference to  FIG. 4  may determine whether the primary request signal should be single-tone or multiple-tone. 
     If the DSS is a single-tone signal (Y branch of  1604 ), the process proceeds to block  1606 , where the transmitting sidelink device may generate and transmit the single-tone DSS. For example, the processing circuit  444 , communication circuit  442  and transceiver  410  shown and described above in reference to  FIG. 4  may generate and transmit the single-tone DSS. At block  1608 , the transmitting sidelink device may then determine whether a secondary request signal (SRS), such as an STS, should be a single-tone signal or a multiple-tone signal. For example, the processing circuit  444  shown and described above in reference to  FIG. 4  may determine whether the secondary request signal should be single-tone or multiple-tone. 
     If the STS is a single-tone signal (Y branch of  1608 ), the process proceeds to block  1610 , where the transmitting sidelink device may generate and transmit the single-tone STS. In some examples, when the STS is a single-tone signal, the transmitting and receiving sidelink devices may each be identified using a tone ID, and the transmitting sidelink device may generate the STS using the tone ID of the receiving sidelink device. For example, the processing circuit  444 , communication circuit  442  and transceiver  410  shown and described above in reference to  FIG. 4  may generate and transmit the single-tone STS. 
     At block  1612 , the transmitting sidelink device may then receive a multiple-tone confirmation signal (CS), such as a DRS, from the receiving sidelink device. In some examples, the multiple-tone DRS may include a source ID of the transmitting sidelink device and various link interference management information, such as a transmit power setting to control power backoff (e.g., within a protection zone), the measured SINR of the link, channel quality information (e.g., CQI), and a reference signal to support Tx-yielding. For example, the communication circuit  442  and transceiver  410  shown and described above in reference to  FIG. 4  may receive the multiple-tone confirmation signal. 
     However, if the STS is not a single-tone signal (N branch of  1608 ), the process proceeds to block  1614 , where the transmitting sidelink device generates and transmits a multiple-tone STS. In some examples, the STS may be a multiple-tone signal to provide reliable destination information and/or transmission duration information. For example, the processing circuit  444 , communication circuit  442  and transceiver  410  shown and described above in reference to  FIG. 4  may generate and transmit the multiple-tone STS. 
     At block  1616 , the transmitting sidelink device may then determine whether a confirmation signal (CS), such as the DRS, should be a single-tone signal or a multiple-tone signal. For example, the processing circuit  444  shown and described above in reference to  FIG. 4  may determine whether the confirmation signal should be single-tone or multiple-tone. 
     If the DRS is a single-tone signal (Y branch of  1616 ), the process proceeds to block  1618 , where the transmitting sidelink device receives a single-tone DRS from the receiving sidelink device. In some examples, as described above, the DRS may be single-tone when the sidelink signal transmit power and MCS are fixed between the transmitting and receiving sidelink devices. The transmit power of the single-tone DRS may further be set to control dimensions of the protection zone around the receiving sidelink device in order to manage interference of a subsequently transmitted sidelink signal from the transmitting sidelink device to the receiving sidelink device. For example, the communication circuit  442  and transceiver  410  shown and described above in reference to  FIG. 4  may receive the single-tone confirmation signal. 
     However, if the confirmation signal is not a single-tone signal (N branch of  1616 ), the process proceeds to block  1612 , where the transmitting sidelink device receives a multiple-tone confirmation signal (e.g., multiple-tone DRS) from the receiving sidelink device. For example, the communication circuit  442  and transceiver  410  shown and described above in reference to  FIG. 4  may receive the multiple-tone confirmation signal. 
     Returning to decision block  1604 , if the primary reference signal (PRS), such as the DSS, is not a single-tone signal (N branch of  1604 ), the process proceeds to block  1620 , where the transmitting sidelink device may generate and transmit a multiple-tone DSS. In some examples, the DSS may be multiple-tone to include a reference signal enabling channel estimation at the receiving sidelink device. For example, the processing circuit  444 , communication circuit  442  and transceiver  410  shown and described above in reference to  FIG. 4  may generate and transmit the multiple-tone DSS. 
     At block  1622 , the transmitting sidelink device may then determine whether the secondary request signal (SRS), such as the STS, should be a single-tone signal or a multiple-tone signal. For example, the processing circuit  444  shown and described above in reference to  FIG. 4  may determine whether the secondary request signal should be single-tone or multiple-tone. If the STS is a single-tone signal (Y branch of  1622 ), the process proceeds to block  1610 , where the transmitting sidelink device may generate and transmit the single-tone STS. At block  1612 , the transmitting sidelink device may then receive a multiple-tone confirmation signal (CS), such as a DRS, from the receiving sidelink device. 
     However, if the STS is not a single-tone signal (N branch of  1622 ), the process proceeds to block  1624 , where the transmitting sidelink device generates a multiple-tone STS. For example, the processing circuit  444 , communication circuit  442  and transceiver  410  shown and described above in reference to  FIG. 4  may generate and transmit the multiple-tone STS. At block  1626 , the transmitting sidelink device may then receive a single-tone confirmation signal (e.g., single-tone DRS) from the receiving sidelink device. For example, the communication circuit  442  and transceiver  410  shown and described above in reference to  FIG. 4  may receive the single-tone confirmation signal. Although blocks  1606 / 1620  and  1610 / 1614 / 1624  are described above as being performed by the same sidelink device, in other examples, block  1606 / 1620  may be performed by another sidelink device when the transmitting sidelink device is not the primary sidelink device. 
       FIG. 17  is a flow chart illustrating an exemplary process  1700  for utilizing a single-tone request signal in sidelink communications in accordance with some aspects of the present disclosure. As described below, some or all illustrated features may be omitted in a particular implementation within the scope of the present disclosure, and some illustrated features may not be required for implementation of all embodiments. In the following description, a sidelink signal transmission is discussed with reference to a transmitting sidelink device and a receiving sidelink device. It will be understood that either device may be the user equipment  126  and/or  128  illustrated in  FIG. 1 ; the scheduling entity  202  illustrated in  FIGS. 2 and 3 ; and/or the scheduled entity  204  illustrated in  FIGS. 2 and 4 . In some examples, the process  1700  may be carried out by any suitable apparatus or means for carrying out the functions or algorithm described below. 
     At block  1702 , the transmitting sidelink device may associate with a receiving sidelink device, and at block  1704 , select a tone ID for the receiving sidelink device. For example, a peer discovery mechanism may be used by an initiating device (e.g., the transmitting or receiving sidelink device) to discover the presence of other devices in a neighborhood or area (e.g., within a radial distance from the location of the initiating device). Once another device of interest is discovered, the initiating device may page the device of interest to associate with the other device and establish a sidelink between the two devices. As part of the association, respective tone IDs may be selected for each device to enable single-tone signaling therebetween. In some examples, the tone IDs may be selected by the initiating device or primary device. In other examples, the tone IDs may be negotiated between the devices. For example, the communication circuit  442 , processing circuit  444 , and transceiver  410  shown and described above in reference to  FIG. 4  may associate with the receiving sidelink device and select the tone ID for the receiving sidelink device. 
     At block  1706 , the transmitting sidelink device may determine whether a primary request signal (PRS), such as a DSS, should be a single-tone signal or a multiple-tone signal. For example, the processing circuit  444  shown and described above in reference to  FIG. 4  may determine whether the primary request signal should be single-tone or multiple-tone. 
     If the DSS is a single-tone signal (Y branch of  1706 ), the process proceeds to block  1708 , where the transmitting sidelink device may generate and transmit the single-tone DSS to indicate the link direction for a sidelink communication. In some examples, the tone ID of the transmitting sidelink device may further be utilized to generate and transmit the single-tone DSS. However, if the DSS is a multiple-tone signal (N branch of  1706 ), the process proceeds to block  1710 , where the transmitting sidelink device may generate and transit the multiple-tone DSS. In this example, the multiple-tone DSS may indicate not only the link direction, but may also include a reference signal to enable channel estimation at the receiving sidelink device. For example, the processing circuit  444 , communication circuit  442  and transceiver  410  shown and described above in reference to  FIG. 4  may generate and transmit the single-tone or multiple-tone DSS. 
     At block  1712 , the transmitting sidelink device may then generate and transmit a single-tone secondary reference signal (SRS), such as a single-tone STS, with the tone ID of the receiving sidelink device. In addition, the single-tone STS may be associated with a fixed duration of time for utilizing the sidelink channel For example, the processing circuit  444 , communication circuit  442  and transceiver  410  shown and described above in reference to  FIG. 4  may generate and transmit the single-tone STS. 
     At block  1714 , the transmitting sidelink device may then receive a multiple-tone confirmation signal (CS), such as a DRS, from the receiving sidelink device. For example, the communication circuit  442  and transceiver  410  shown and described above in reference to  FIG. 4  may receive the multiple-tone confirmation signal. Although blocks  1708 / 1710  and  1712  are described above as being performed by the same sidelink device, in other examples, block  1708 / 1710  may be performed by another sidelink device when the transmitting sidelink device is not the primary sidelink device. 
       FIG. 18  is a flow chart illustrating an exemplary process  1800  for utilizing single-tone and multiple-tone sidelink signaling to control the dimensions of a protection zone in accordance with some aspects of the present disclosure. As described below, some or all illustrated features may be omitted in a particular implementation within the scope of the present disclosure, and some illustrated features may not be required for implementation of all embodiments. In the following description, a sidelink signal transmission is discussed with reference to a transmitting sidelink device and a receiving sidelink device. It will be understood that either device may be the user equipment  126  and/or  128  illustrated in  FIG. 1 ; the scheduling entity  202  illustrated in  FIGS. 2 and 3 ; and/or the scheduled entity  204  illustrated in  FIGS. 2 and 4 . In some examples, the process  1800  may be carried out by any suitable apparatus or means for carrying out the functions or algorithm described below. 
     At block  1802 , the transmitting sidelink device may determine whether the request signal (RS) (e.g., one or both of the DSS and/or STS) should be a single-tone signal or a multiple-tone signal. In addition, the transmitting sidelink device may determine whether the confirmation signal (CS) (e.g., DRS) should be a single-tone signal or a multiple-tone signal. In some examples, the transmitting and receiving sidelink devices may negotiate whether the request signal (e.g., one or both of the DSS and/or STS) and/or the confirmation signal may be single-tone or multiple-tone signals during the initial association therebetween. In other examples, the network (e.g., scheduling entity) may indicate whether the request signal and confirmation signal should be single-tone or multiple-tone signals. For example, the processing circuit  444  shown and described above in reference to  FIG. 4  may determine whether the request signal should be single-tone and the confirmation signal should be multiple-tone. 
     If the request signal includes a single-tone signal (e.g., at least one of the DSS and/or STS is a single-tone signal) and the confirmation signal is a multiple-tone signal (Y branch of  1802 ), the process proceeds to block  1804 , where the transmitting sidelink device may generate and transmit the single-tone request signal. In some examples, the transmitting sidelink device transmits both the DSS and STS, at least one of which is a single-tone signal. In other examples, the transmitting sidelink device transmits a single-tone STS, while another sidelink device transmits a single-tone DSS or multiple-tone DSS when the transmitting sidelink device is not the primary sidelink device. For example, the processing circuit  444 , communication circuit  442  and transceiver  410  shown and described above in reference to  FIG. 4  may generate and transmit the single-tone request signal. 
     At block  1806 , the transmitting sidelink device may then receive a multiple-tone confirmation signal from the receiving sidelink device. In some examples, the multiple-tone confirmation signal may include a transmit power selected to control the dimensions of a protection zone around the receiving sidelink device, thus managing interference for the sidelink signal. For example, the communication circuit  442  and transceiver  410  shown and described above in reference to  FIG. 4  may receive the multiple-tone confirmation signal. 
     However, if the request signal is not a single-tone signal (e.g., at least the STS is not a single-tone signal) and the confirmation signal (e.g., DRS) is not a multiple-tone signal (N branch of  1802 ), the process proceeds to block  1808 , where the transmitting sidelink device generates a multiple-tone request signal (e.g., at least a multiple-tone STS). In some examples, the transmitting sidelink device transmits both the DSS and STS, where at least the STS is a multiple-tone signal. In other examples, the transmitting sidelink device transmits a multiple-tone STS, while another sidelink device transmits a single-tone DSS or multiple-tone DSS when the transmitting sidelink device is not the primary sidelink device. For example, the processing circuit  444 , communication circuit  442  and transceiver  410  shown and described above in reference to  FIG. 4  may generate and transmit the multiple-tone request signal. 
     At block  1810 , the transmitting sidelink device may then receive a single-tone confirmation signal from the receiving sidelink device. In some examples, the single-tone confirmation signal may include a transmit power selected to control the dimensions of a protection zone around the receiving sidelink device, thus managing interference for the sidelink signal. For example, the communication circuit  442  and transceiver  410  shown and described above in reference to  FIG. 4  may receive the single-tone confirmation signal. 
     Several aspects of a wireless communication network have been presented with reference to an exemplary implementation. As those skilled in the art will readily appreciate, various aspects described throughout this disclosure may be extended to other telecommunication systems, network architectures and communication standards. 
     By way of example, various aspects may be implemented within other systems defined by 3GPP, such as Long-Term Evolution (LTE), the Evolved Packet System (EPS), the Universal Mobile Telecommunication System (UMTS), and/or the Global System for Mobile (GSM). Various aspects may also be extended to systems defined by the 3rd Generation Partnership Project 2 (3GPP2), such as CDMA 2000 and/or Evolution-Data Optimized (EV-DO). Other examples may be implemented within systems employing IEEE 802.11 (Wi-Fi), IEEE 802.16 (WiMAX), IEEE 802.20, Ultra-Wideband (UWB), Bluetooth, and/or other suitable systems. The actual telecommunication standard, network architecture, and/or communication standard employed will depend on the specific application and the overall design constraints imposed on the system. 
     Within the present disclosure, the word “exemplary” is used to mean “serving as an example, instance, or illustration.” Any implementation or aspect described herein as “exemplary” is not necessarily to be construed as preferred or advantageous over other aspects of the disclosure. Likewise, the term “aspects” does not require that all aspects of the disclosure include the discussed feature, advantage or mode of operation. The term “coupled” is used herein to refer to the direct or indirect coupling between two objects. For example, if object A physically touches object B, and object B touches object C, then objects A and C may still be considered coupled to one another—even if they do not directly physically touch each other. For instance, a first object may be coupled to a second object even though the first object is never directly physically in contact with the second object. The terms “circuit” and “circuitry” are used broadly, and intended to include both hardware implementations of electrical devices and conductors that, when connected and configured, enable the performance of the functions described in the present disclosure, without limitation as to the type of electronic circuits, as well as software implementations of information and instructions that, when executed by a processor, enable the performance of the functions described in the present disclosure. 
     One or more of the components, steps, features and/or functions illustrated in  FIGS. 1-18  may be rearranged and/or combined into a single component, step, feature or function or embodied in several components, steps, or functions. Additional elements, components, steps, and/or functions may also be added without departing from novel features disclosed herein. The apparatus, devices, and/or components illustrated in  FIGS. 1-4  may be configured to perform one or more of the methods, features, or steps described herein. The novel algorithms described herein may also be efficiently implemented in software and/or embedded in hardware. 
     It is to be understood that the specific order or hierarchy of steps in the methods disclosed is an illustration of exemplary processes. Based upon design preferences, it is understood that the specific order or hierarchy of steps in the methods may be rearranged. The accompanying method claims present elements of the various steps in a sample order, and are not meant to be limited to the specific order or hierarchy presented unless specifically recited therein. 
     The previous description is provided to enable any person skilled in the art to practice the various aspects described herein. Various modifications to these aspects will be readily apparent to those skilled in the art, and the generic principles defined herein may be applied to other aspects. Thus, the claims are not intended to be limited to the aspects shown herein, but are to be accorded the full scope consistent with the language of the claims, wherein reference to an element in the singular is not intended to mean “one and only one” unless specifically so stated, but rather “one or more.” Unless specifically stated otherwise, the term “some” refers to one or more. A phrase referring to “at least one of” a list of items refers to any combination of those items, including single members. As an example, “at least one of: a, b, or c” is intended to cover: a; b; c; a and b; a and c; b and c; and a, b and c. All structural and functional equivalents to the elements of the various aspects described throughout this disclosure that are known or later come to be known to those of ordinary skill in the art are expressly incorporated herein by reference and are intended to be encompassed by the claims. Moreover, nothing disclosed herein is intended to be dedicated to the public regardless of whether such disclosure is explicitly recited in the claims. No claim element is to be construed under the provisions of 35 U.S.C. § 112(f) unless the element is expressly recited using the phrase “means for” or, in the case of a method claim, the element is recited using the phrase “step for.”