Patent Publication Number: US-11044581-B2

Title: Signaling for round trip time (RTT) based positioning using stronger path tracking

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     The present Application for Patent claims priority under 35 U.S.C. § 119 to Greek Patent Application No. 20190100039, entitled “SIGNALING FOR ROUND TRIP TIME (RTT)-BASED POSITIONING USING STRONG PATH TRACKING”, filed Jan. 21, 2019, assigned to the assignee hereof, and expressly incorporated herein by reference in its entirety. 
     INTRODUCTION 
     1. Technical Field 
     Various aspects described herein generally relate to wireless communication systems, and more particularly, to signaling for round trip time (RTT)-based positioning using stronger path tracking for wireless networks, e.g., in new radio (NR). 
     2. Background 
     Wireless communication systems have developed through various generations, including a first-generation analog wireless phone service (1G), a second-generation (2G) digital wireless phone service (including interim 2.5G and 2.75G networks), a third-generation (3G) high speed data, Internet-capable wireless service and a fourth-generation (4G) service (e.g., Long Term Evolution (LTE) or WiMax). There are presently many different types of wireless communication systems in use, including cellular and personal communications service (PCS) systems. Examples of known cellular systems include the cellular analog advanced mobile phone system (AMPS), and digital cellular systems based on code division multiple access (CDMA), frequency division multiple access (FDMA), time division multiple access (TDMA), the Global System for Mobile access (GSM) variation of TDMA, etc. 
     A fifth generation (5G) mobile standard, referred to as New Radio (NR), calls for higher data transfer speeds, greater numbers of connections, and better coverage, among other improvements. The 5G standard, according to the Next Generation Mobile Networks Alliance, is designed to provide data rates of several tens of megabits per second to each of tens of thousands of users, with 1 gigabit per second to tens of workers on an office floor. Several hundreds of thousands of simultaneous connections should be supported in order to support large sensor deployments. Consequently, the spectral efficiency of 5G mobile communications should be significantly enhanced compared to the current 4G standard. Furthermore, signaling efficiencies should be enhanced and latency should be substantially reduced compared to current standards. 
     Some wireless communication networks, such as 5G, support operation at very high and even extremely-high frequency (EHF) bands, such as millimeter wave (mmW) frequency bands (generally, wavelengths of 1 mm to 10 mm, or 30 to 300 GHz). These extremely high frequencies may support very high throughput such as up to six gigabits per second (Gbps). 
     To support position estimations in terrestrial wireless networks, a mobile device can be configured to measure and report the observed time difference of arrival (OTDOA) or reference signal timing difference (RSTD) between reference RF signals received from two or more network nodes (e.g., different base stations or different transmission points (e.g., antennas) belonging to the same base station). The mobile device can also be configured to report the time of arrival (ToA) of RF signals. 
     With OTDOA, when the mobile device reports the time difference of arrival (TDOA) between RF signals from two network nodes, the location of the mobile device is then known to lie on a hyperbola with the locations of the two network nodes as the foci. Measuring TDOAs between multiple pairs of network nodes allows for solving for the mobile device&#39;s position as intersections of the hyperbolas. 
     Round trip time (RTT) is another technique for determining a position of a mobile device. RTT is a two-way messaging technique (network node to mobile device and mobile device to network node), with both the mobile device and the network node reporting their receive-to-transmit (Rx-Tx) time differences to a positioning entity, such as a location server or location management function (LMF), that computes the mobile device&#39;s position. This allows for computing the back-and-forth flight time between the mobile device and the network node. The location of the mobile device is then known to lie on a circle with a center at the network node&#39;s position. Reporting RTTs with multiple network nodes allows the positioning entity to solve for the mobile device&#39;s position as the intersections of the circles. 
     SUMMARY 
     This summary identifies features of some example aspects, and is not an exclusive or exhaustive description of the disclosed subject matter. Whether features or aspects are included in, or omitted from this summary is not intended as indicative of relative importance of such features. Additional features and aspects are described, and will become apparent to persons skilled in the art upon reading the following detailed description and viewing the drawings that form a part thereof. 
     In accordance with the various aspects disclosed herein, at least one aspect includes, a method performed by a user equipment (UE), the method including: receiving one or more downlink reference signals (DL RSs) from one or more transmission-reception points (TRPs); transmitting one or more uplink reference signals (UL RSs) to the one or more TRPs; generating a measurement report for the one or more TRPs; and transmitting the measurement report, where the measurement report includes, for at least one TRP of the one or more TRPs, a UE time difference and an offset of the at least one TRP, where the UE time difference is a difference of a UE transmission time of the UL RS to the at least one TRP and an earliest reception time representing a time of arrival (TOA) at the UE of an earliest path of the DL RS from the at least one TRP, and where the offset is a difference of a stronger reception time representing a TOA at the UE of a stronger path of the DL RS from the at least one TRP and the earliest reception time. 
     In accordance with the various aspects disclosed herein, at least one aspect includes, a method performed by a transmission-reception point (TRP), the method including: transmitting a downlink reference signal (DL RS) to a user equipment (UE); receiving an uplink reference signal (UL RS) corresponding to the DL RS; and receiving a measurement report from the UE, where the measurement report includes a UE time difference and an offset of the TRP, where the UE time difference is a difference of a UE transmission time of the UL RS to the TRP and an earliest reception time representing a time of arrival (TOA) at the UE of an earliest path of the DL RS from the TRP, and where the offset is a difference of a stronger reception time representing a TOA at the UE of a stronger path of the DL RS from the TRP and the earliest reception time. 
     In accordance with the various aspects disclosed herein, at least one aspect includes, a user equipment (UE), including: a transceiver; a memory; and a processor communicatively coupled to the transceiver and the memory, the processor being configured to: receive one or more downlink reference signals (DL RSs) from one or more transmission-reception points (TRPs); transmit one or more uplink reference signals (UL RSs) to the one or more TRPs; generate a measurement report for the one or more TRPs; and transmit the measurement report, where the measurement report includes, for at least one TRP of the one or more TRPs, a UE time difference and an offset of the at least one TRP, where the UE time difference is a difference of a UE transmission time of the UL RS to the at least one TRP and an earliest reception time representing a time of arrival (TOA) at the UE of an earliest path of the DL RS from the at least one TRP, and where the offset is a difference of a stronger reception time representing a TOA at the UE of a stronger path of the DL RS from the at least one TRP and the earliest reception time. 
     In accordance with the various aspects disclosed herein, at least one aspect includes, a transmission-reception point (TRP) including: a transceiver; a memory; and a processor communicatively coupled to the transceiver and the memory, the processor being configured to: transmit a downlink reference signal (DL RS) to a user equipment (UE) at; receive an uplink reference signal (UL RS) corresponding to the DL RS; and receive a measurement report from the UE, where measurement report includes a UE time difference and an offset of the TRP, where the UE time difference is a difference of a UE transmission time of the UL RS to the TRP and an earliest reception time representing a time of arrival (TOA) at the UE of an earliest path of the DL RS from the TRP, and where the offset is a difference of a stronger reception time representing a TOA at the UE of a stronger path of the DL RS from TRP and the earliest reception time. 
     In accordance with the various aspects disclosed herein, at least one aspect includes, a user equipment (UE) including: means for receiving one or more downlink reference signals (DL RSs) from one or more transmission-reception points (TRPs); means for transmitting one or more uplink reference signals (UL RSs) to the one or more TRPs; means for generating a measurement report for the one or more TRPs; and means for transmitting the measurement report, where the measurement report includes, for at least one TRP of the one or more TRPs, a UE time difference and an offset of the at least one TRP, where the UE time difference is a difference of a UE transmission time of the UL RS to the at least one TRP and an earliest reception time representing a time of arrival (TOA) at the UE of an earliest path of the DL RS from the at least one TRP, and where the offset is a difference of a stronger reception time representing a TOA at the UE of a stronger path of the DL RS from the at least one TRP and the earliest reception time. 
     In accordance with the various aspects disclosed herein, at least one aspect includes, a transmission-reception point (TRP) including: means for transmitting a downlink reference signal (DL RS) to a user equipment (UE) at T 1 ; means for receiving an uplink reference signal (UL RS) corresponding to the DL RS; and means for receiving a measurement report from the UE, where the measurement report includes a UE time difference and an offset of the TRP, where the UE time difference is a difference of a UE transmission time of the UL RS to the TRP and an earliest reception time representing a time of arrival (TOA) at the UE of an earliest path of the DL RS from the TRP, and where the offset is a difference of a stronger reception time representing a TOA at the UE of a stronger path of the DL RS from the TRP and the earliest reception time. 
     Other objects and advantages associated with the aspects disclosed herein will be apparent to those skilled in the art based on the accompanying drawings and detailed description. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The accompanying drawings are presented to aid in the description of examples of one or more aspects of the disclosed subject matter and are provided solely for illustration of the examples and not limitation thereof: 
         FIG. 1  illustrates an exemplary wireless communications system in accordance with one or more aspects of the disclosure; 
         FIGS. 2A and 2B  illustrate example wireless network structures in accordance with one or more aspects of the disclosure; 
         FIGS. 3A to 3C  are simplified block diagrams of several sample aspects of components that may be employed in a UE, a TRP, and a network entity, respectively, and configured to support communication in accordance with one or more aspects of the disclosure; 
         FIG. 4  illustrates a scenario for determining a position of a UE through a multi-RTT procedure in accordance with one or more aspects of the disclosure; 
         FIG. 5  illustrates a diagram of timings of a conventional technique for determining a round trip time (RTT) between a cell; 
         FIG. 6  illustrates a scenario in which measurement reports for multiple cells are reported by the UE; 
         FIG. 7  illustrates a diagram of exemplary timings for determining an RTT between a cell and a UE in accordance with an aspect of the disclosure; 
         FIG. 8  illustrates an exemplary method performed a UE for measurement reporting in accordance with an aspect of the disclosure; 
         FIG. 9  illustrates an example process performed by a UE to measure downlink reference signal from a cell in accordance with an aspect of the disclosure; 
         FIG. 10  illustrates an example process performed by a UE to transmit an uplink reference signal to a cell in accordance with an aspect of the disclosure; 
         FIG. 11  illustrates an example process performed by a UE to generate a measurement report in accordance with an aspect of the disclosure; 
         FIG. 12  illustrates an exemplary method performed a cell for determining an RTT between the cell and a UE in accordance with an aspect of the disclosure; 
         FIGS. 13 and 14  illustrate exemplary methods, according to aspects of the disclosure. 
         FIGS. 15 and 16  are other simplified block diagrams of several sample aspects of apparatuses configured to support positioning and communication as taught herein. 
     
    
    
     DETAILED DESCRIPTION 
     Aspects of the disclosure are provided in the following description and related drawings directed to various examples provided for illustration purposes. Alternate aspects may be devised without departing from the scope of the disclosure. Additionally, well-known elements of the disclosure will not be described in detail or will be omitted so as not to obscure the relevant details of the disclosure. 
     The words “exemplary” and/or “example” are used herein to mean “serving as an example, instance, or illustration.” Any aspect described herein as “exemplary” and/or “example” is not necessarily to be construed as preferred or advantageous over other aspects. Likewise, the term “aspects of the disclosure” does not require that all aspects of the disclosure include the discussed feature, advantage or mode of operation. 
     Those of skill in the art will appreciate that the information and signals described below may be represented using any of a variety of different technologies and techniques. For example, data, instructions, commands, information, signals, bits, symbols, and chips that may be referenced throughout the description below may be represented by voltages, currents, electromagnetic waves, magnetic fields or particles, optical fields or particles, or any combination thereof, depending in part on the particular application, in part on the desired design, in part on the corresponding technology, etc. 
     Further, many aspects are described in terms of sequences of actions to be performed by, for example, elements of a computing device. It will be recognized that various actions described herein can be performed by specific circuits (e.g., application specific integrated circuits (ASICs)), by program instructions being executed by one or more processors, or by a combination of both. Additionally, the sequence(s) of actions described herein can be considered to be embodied entirely within any form of non-transitory computer-readable storage medium having stored therein a corresponding set of computer instructions that, upon execution, would cause or instruct an associated processor of a device to perform the functionality described herein. Thus, the various aspects of the disclosure may be embodied in a number of different forms, all of which have been contemplated to be within the scope of the claimed subject matter. In addition, for each of the aspects described herein, the corresponding form of any such aspects may be described herein as, for example, “logic configured to” perform the described action. 
     As used herein, the terms “user equipment” (UE) and “base station” are not intended to be specific or otherwise limited to any particular radio access technology (RAT), unless otherwise noted. In general, a UE may be any wireless communication device (e.g., a mobile phone, router, tablet computer, laptop computer, tracking device, wearable (e.g., smartwatch, glasses, augmented reality (AR)/virtual reality (VR) headset, etc.), vehicle (e.g., automobile, motorcycle, bicycle, etc.), Internet of Things (IoT) device, etc.) used by a user to communicate over a wireless communications network. A UE may be mobile or may (e.g., at certain times) be stationary, and may communicate with a radio access network (RAN). As used herein, the term “UE” may be referred to interchangeably as an “access terminal” or “AT,” a “client device,” a “wireless device,” a “subscriber device,” a “subscriber terminal,” a “subscriber station,” a “user terminal” or UT, a “mobile terminal,” a “mobile station,” or variations thereof. Generally, UEs can communicate with a core network via a RAN, and through the core network the UEs can be connected with external networks such as the Internet and with other UEs. Of course, other mechanisms of connecting to the core network and/or the Internet are also possible for the UEs, such as over wired access networks, wireless local area network (WLAN) networks (e.g., based on IEEE 802.11, etc.) and so on. 
     A base station may operate according to one of several RATs in communication with UEs depending on the network in which it is deployed, and may be alternatively referred to as an access point (AP), a network node, a NodeB, an evolved NodeB (eNB), a New Radio (NR) Node B (also referred to as a gNB or gNodeB), etc. In addition, in some systems a base station may provide purely edge node signaling functions while in other systems it may provide additional control and/or network management functions. A communication link through which UEs can send signals to a base station is called an uplink (UL) channel (e.g., a reverse traffic channel, a reverse control channel, an access channel, etc.). A communication link through which the base station can send signals to UEs is called a downlink (DL) or forward link channel (e.g., a paging channel, a control channel, a broadcast channel, a forward traffic channel, etc.). As used herein the term traffic channel (TCH) can refer to either an UL/reverse or DL/forward traffic channel. 
     The term “base station” may refer to a single physical transmission-reception point (TRP) or to multiple physical TRPs that may or may not be co-located. For example, where the term “base station” refers to a single physical TRP, the physical TRP may be an antenna of the base station corresponding to a cell of the base station. Where the term “base station” refers to multiple co-located physical TRPs, the physical TRPs may be an array of antennas (e.g., as in a multiple-input multiple-output (MIMO) system or where the base station employs beamforming) of the base station. Where the term “base station” refers to multiple non-co-located physical TRPs, the physical TRPs may be a distributed antenna system (DAS) (a network of spatially separated antennas connected to a common source via a transport medium) or a remote radio head (RRH) (a remote base station connected to a serving base station). Alternatively, the non-co-located physical TRPs may be the serving base station receiving the measurement report from the UE and a neighbor base station whose reference RF signals the UE is measuring. Because a TRP is the point from which a base station transmits and receives wireless signals, as used herein, references to transmission from or reception at a base station are to be understood as referring to a particular TRP of the base station. 
     An “RF signal” comprises an electromagnetic wave of a given frequency that transports information through the space between a transmitter and a receiver. As used herein, a transmitter may transmit a single “RF signal” or multiple “RF signals” to a receiver. However, the receiver may receive multiple “RF signals” corresponding to each transmitted RF signal due to the propagation characteristics of RF signals through multipath channels. The same transmitted RF signal on different paths between the transmitter and receiver may be referred to as a “multipath” RF signal. 
     According to various aspects,  FIG. 1  illustrates an exemplary wireless communications system  100 . The wireless communications system  100  (which may also be referred to as a wireless wide area network (WWAN)) may include various base stations  102  and various UEs  104 . The base stations  102  may include macro cell base stations (high power cellular base stations) and/or small cell base stations (low power cellular base stations). In an aspect, the macro cell base station may include eNBs where the wireless communications system  100  corresponds to an LTE network, or gNBs where the wireless communications system  100  corresponds to a NR network, or a combination of both, and the small cell base stations may include femtocells, picocells, microcells, etc. 
     The base stations  102  may collectively form a RAN and interface with a core network  170  (e.g., an evolved packet core (EPC) or next generation core (NGC)) through backhaul links  122 , and through the core network  170  to one or more location servers  172 . In addition to other functions, the base stations  102  may perform functions that relate to one or more of transferring user data, radio channel ciphering and deciphering, integrity protection, header compression, mobility control functions (e.g., handover, dual connectivity), inter-cell interference coordination, connection setup and release, load balancing, distribution for non-access stratum (NAS) messages, NAS node selection, synchronization, RAN sharing, multimedia broadcast multicast service (MBMS), subscriber and equipment trace, RAN information management (RIM), paging, positioning, and delivery of warning messages. The base stations  102  may communicate with each other directly or indirectly (e.g., through the EPC/NGC) over backhaul links  134 , which may be wired or wireless. 
     The base stations  102  may wirelessly communicate with the UEs  104 . Each of the base stations  102  may provide communication coverage for a respective geographic coverage area  110 . In an aspect, one or more cells may be supported by a base station  102  in each coverage area  110 . A “cell” is a logical communication entity used for communication with a base station (e.g., over some frequency resource, referred to as a carrier frequency, component carrier, carrier, band, or the like), and may be associated with an identifier (e.g., a physical cell identifier (PCI), a virtual cell identifier (VCI)) for distinguishing cells operating via the same or a different carrier frequency. In some cases, different cells may be configured according to different protocol types (e.g., machine-type communication (MTC), narrowband IoT (NB-IoT), enhanced mobile broadband (eMBB), or others) that may provide access for different types of UEs. Because a cell is supported by a specific base station, the term “cell” may refer to either or both the logical communication entity and the base station that supports it, depending on the context. In some cases, the term “cell” may also refer to a geographic coverage area of a base station (e.g., a sector), insofar as a carrier frequency can be detected and used for communication within some portion of geographic coverage areas  110 . 
     While neighboring macro cell base station  102  geographic coverage areas  110  may partially overlap (e.g., in a handover region), some of the geographic coverage areas  110  may be substantially overlapped by a larger geographic coverage area  110 . For example, a small cell base station  102 ′ may have a coverage area  110 ′ that substantially overlaps with the coverage area  110  of one or more macro cell base stations  102 . A network that includes both small cell and macro cell base stations may be known as a heterogeneous network. A heterogeneous network may also include home eNBs (HeNBs), which may provide service to a restricted group known as a closed subscriber group (CSG). 
     The communication links  120  between the base stations  102  and the UEs  104  may include UL (also referred to as reverse link) transmissions from a UE  104  to a base station  102  and/or downlink (DL) (also referred to as forward link) transmissions from a base station  102  to a UE  104 . The communication links  120  may use MIMO antenna technology, including spatial multiplexing, beamforming, and/or transmit diversity. The communication links  120  may be through one or more carrier frequencies. Allocation of carriers may be asymmetric with respect to DL and UL (e.g., more or less carriers may be allocated for DL than for UL). 
     The wireless communications system  100  may further include a wireless local area network (WLAN) access point (AP)  150  in communication with WLAN stations (STAs)  152  via communication links  154  in an unlicensed frequency spectrum (e.g., 5 GHz). When communicating in an unlicensed frequency spectrum, the WLAN STAs  152  and/or the WLAN AP  150  may perform a clear channel assessment (CCA) or listen before talk (LBT) procedure prior to communicating in order to determine whether the channel is available. 
     The small cell base station  102 ′ may operate in a licensed and/or an unlicensed frequency spectrum. When operating in an unlicensed frequency spectrum, the small cell base station  102 ′ may employ LTE or NR technology and use the same 5 GHz unlicensed frequency spectrum as used by the WLAN AP  150 . The small cell base station  102 ′, employing LTE/5G in an unlicensed frequency spectrum, may boost coverage to and/or increase capacity of the access network. NR in unlicensed spectrum may be referred to as NR-U. LTE in an unlicensed spectrum may be referred to as LTE-U, licensed assisted access (LAA), or MulteFire. 
     The wireless communications system  100  may further include a millimeter wave (mmW) base station  180  that may operate in mmW frequencies and/or near mmW frequencies in communication with a UE  182 . Extremely high frequency (EHF) is part of the RF in the electromagnetic spectrum. EHF has a range of 30 GHz to 300 GHz and a wavelength between 1 millimeter and 10 millimeters. Radio waves in this band may be referred to as a millimeter wave. Near mmW may extend down to a frequency of 3 GHz with a wavelength of 100 millimeters. The super high frequency (SHF) band extends between 3 GHz and 30 GHz, also referred to as centimeter wave. Communications using the mmW/near mmW radio frequency band have high path loss and a relatively short range. The mmW base station  180  and the UE  182  may utilize beamforming (transmit and/or receive) over a mmW communication link  184  to compensate for the extremely high path loss and short range. Further, it will be appreciated that in alternative configurations, one or more base stations  102  may also transmit using mmW or near mmW and beamforming. Accordingly, it will be appreciated that the foregoing illustrations are merely examples and should not be construed to limit the various aspects disclosed herein. 
     Transmit beamforming is a technique for focusing an RF signal in a specific direction. Traditionally, when a network node (e.g., a base station) broadcasts an RF signal, it broadcasts the signal in all directions (omni-directionally). With transmit beamforming, the network node determines where a given target device (e.g., a UE) is located (relative to the transmitting network node) and projects a stronger downlink RF signal in that specific direction, thereby providing a faster (in terms of data rate) and stronger RF signal for the receiving device(s). To change the directionality of the RF signal when transmitting, a network node can control the phase and relative amplitude of the RF signal at each of the one or more transmitters that are broadcasting the RF signal. For example, a network node may use an array of antennas (referred to as a “phased array” or an “antenna array”) that creates a beam of RF waves that can be “steered” to point in different directions, without actually moving the antennas. Specifically, the RF current from the transmitter is fed to the individual antennas with the correct phase relationship so that the radio waves from the separate antennas add together to increase the radiation in a desired direction, while cancelling to suppress radiation in undesired directions. 
     Transmit beams may be quasi-collocated, meaning that they appear to the receiver (e.g., a UE) as having the same parameters, regardless of whether or not the transmitting antennas of the network node themselves are physically collocated. In NR, there are four types of quasi-collocation (QCL) relations. Specifically, a QCL relation of a given type means that certain parameters about a second reference RF signal on a second beam can be derived from information about a source reference RF signal on a source beam. Thus, if the source reference RF signal is QCL Type A, the receiver can use the source reference RF signal to estimate the Doppler shift, Doppler spread, average delay, and delay spread of a second reference RF signal transmitted on the same channel. If the source reference RF signal is QCL Type B, the receiver can use the source reference RF signal to estimate the Doppler shift and Doppler spread of a second reference RF signal transmitted on the same channel. If the source reference RF signal is QCL Type C, the receiver can use the source reference RF signal to estimate the Doppler shift and average delay of a second reference RF signal transmitted on the same channel. If the source reference RF signal is QCL Type D, the receiver can use the source reference RF signal to estimate the spatial receive parameter of a second reference RF signal transmitted on the same channel. 
     In receive beamforming, the receiver uses a receive beam to amplify RF signals detected on a given channel. For example, the receiver can increase the gain setting and/or adjust the phase setting of an array of antennas in a particular direction to amplify (e.g., to increase the gain level of) the RF signals received from that direction. Thus, when a receiver is said to beamform in a certain direction, it means the beam gain in that direction is high relative to the beam gain along other directions, or the beam gain in that direction is the highest compared to the beam gain in that direction of all other receive beams available to the receiver. This results in a stronger received signal strength (e.g., reference signal received power (RSRP), reference signal received quality (RSRQ), signal-to-interference-plus-noise ratio (SINR), etc.) of the RF signals received from that direction. 
     Receive beams may be spatially related. A spatial relation means that parameters for a transmit beam for a second reference signal can be derived from information about a receive beam for a first reference signal. For example, a UE may use a particular receive beam to receive a reference downlink reference signal (e.g., synchronization signal block (SSB)) from a base station. The UE can then form a transmit beam for sending an uplink reference signal (e.g., sounding reference signal (SRS)) to that base station based on the parameters of the receive beam. 
     Note that a “downlink” beam may be either a transmit beam or a receive beam, depending on the entity forming it. For example, if a base station is forming the downlink beam to transmit a reference signal to a UE, the downlink beam is a transmit beam. If the UE is forming the downlink beam, however, it is a receive beam to receive the downlink reference signal. Similarly, an “uplink” beam may be either a transmit beam or a receive beam, depending on the entity forming it. For example, if a base station is forming the uplink beam, it is an uplink receive beam, and if a UE is forming the uplink beam, it is an uplink transmit beam. 
     In 5G, the frequency spectrum in which wireless nodes (e.g., base stations  102 / 180 , UEs  104 / 182 ) operate is divided into multiple frequency ranges, FR 1  (from 450 to 6000 MHz), FR 2  (from 24250 to 52600 MHz), FR 3  (above 52600 MHz), and FR 4  (between FR 1  and FR 2 ). In a multi-carrier system, such as 5G, one of the carrier frequencies is referred to as the “primary carrier” or “anchor carrier” or “primary serving cell” or “PCell,” and the remaining carrier frequencies are referred to as “secondary carriers” or “secondary serving cells” or “SCells.” In carrier aggregation, the anchor carrier is the carrier operating on the primary frequency (e.g., FR 1 ) utilized by a UE  104 / 182  and the cell in which the UE  104 / 182  either performs the initial radio resource control (RRC) connection establishment procedure or initiates the RRC connection re-establishment procedure. The primary carrier carries all common and UE-specific control channels, and may be a carrier in a licensed frequency (however, this is not always the case). A secondary carrier is a carrier operating on a second frequency (e.g., FR 2 ) that may be configured once the RRC connection is established between the UE  104  and the anchor carrier and that may be used to provide additional radio resources. In some cases, the secondary carrier may be a carrier in an unlicensed frequency. The secondary carrier may contain only necessary signaling information and signals, for example, those that are UE-specific may not be present in the secondary carrier, since both primary uplink and downlink carriers are typically UE-specific. This means that different UEs  104 / 182  in a cell may have different downlink primary carriers. The same is true for the uplink primary carriers. The network is able to change the primary carrier of any UE  104 / 182  at any time. This is done, for example, to balance the load on different carriers. Because a “serving cell” (whether a PCell or an SCell) corresponds to a carrier frequency/component carrier over which some base station is communicating, the term “cell,” “serving cell,” “component carrier,” “carrier frequency,” and the like can be used interchangeably. 
     For example, still referring to  FIG. 1 , one of the frequencies utilized by the macro cell base stations  102  may be an anchor carrier (or “PCell”) and other frequencies utilized by the macro cell base stations  102  and/or the mmW base station  180  may be secondary carriers (“SCells”). The simultaneous transmission and/or reception of multiple carriers enables the UE  104 / 182  to significantly increase its data transmission and/or reception rates. For example, two 20 MHz aggregated carriers in a multi-carrier system would theoretically lead to a two-fold increase in data rate (i.e., 40 MHz), compared to that attained by a single 20 MHz carrier. 
     The wireless communications system  100  may further include one or more UEs, such as UE  190 , that connects indirectly to one or more communication networks via one or more device-to-device (D2D) peer-to-peer (P2P) links. In the example of 1, UE  190  has a D2D P2P link  192  with one of the UEs  104  connected to one of the base stations  102  (e.g., through which UE  190  may indirectly obtain cellular connectivity) and a D2D P2P link  194  with WLAN STA  152  connected to the WLAN AP  150  (through which UE  190  may indirectly obtain WLAN-based Internet connectivity). In an example, the D2D P2P links  192  and  194  may be supported with any well-known D2D RAT, such as LTE Direct (LTE-D), WiFi Direct (WiFi-D), Bluetooth®, and so on. 
     The wireless communications system  100  may further include a UE  164  that may communicate with a macro cell base station  102  over a communication link  120  and/or the mmW base station  180  over a mmW communication link  184 . For example, the macro cell base station  102  may support a PCell and one or more SCells for the UE  164  and the mmW base station  180  may support one or more SCells for the UE  164 . 
     According to various aspects, 2A illustrates an example wireless network structure  200 . For example, an NGC  210  (also referred to as a “5GC”) can be viewed functionally as control plane functions  214  (e.g., UE registration, authentication, network access, gateway selection, etc.) and user plane functions  212 , (e.g., UE gateway function, access to data networks, IP routing, etc.) which operate cooperatively to form the core network. User plane interface (NG-U)  213  and control plane interface (NG-C)  215  connect the gNB  222  to the NGC  210  and specifically to the control plane functions  214  and user plane functions  212 . In an additional configuration, an eNB  224  may also be connected to the NGC  210  via NG-C  215  to the control plane functions  214  and NG-U  213  to user plane functions  212 . Further, eNB  224  may directly communicate with gNB  222  via a backhaul connection  223 . In some configurations, the New RAN  220  may only have one or more gNBs  222 , while other configurations include one or more of both eNBs  224  and gNBs  222 . Either gNB  222  or eNB  224  may communicate with UEs  204  (e.g., any of the UEs depicted in  1 ). Another optional aspect may include location server  230 , which may be in communication with the NGC  210  to provide location assistance for UEs  204 . The location server  230  can be implemented as a plurality of separate servers (e.g., physically separate servers, different software modules on a single server, different software modules spread across multiple physical servers, etc.), or alternately may each correspond to a single server. The location server  230  can be configured to support one or more location services for UEs  204  that can connect to the location server  230  via the core network, NGC  210 , and/or via the Internet (not illustrated). Further, the location server  230  may be integrated into a component of the core network, or alternatively may be external to the core network. 
     According to various aspects,  2 B illustrates another example wireless network structure  250 . For example, an NGC  260  (also referred to as a “5GC”) can be viewed functionally as control plane functions, provided by an access and mobility management function (AMF)/user plane function (UPF)  264 , and user plane functions, provided by a session management function (SMF)  262 , which operate cooperatively to form the core network (i.e., NGC  260 ). User plane interface  263  and control plane interface  265  connect the eNB  224  to the NGC  260  and specifically to SMF  262  and AMF/UPF  264 , respectively. In an additional configuration, a gNB  222  may also be connected to the NGC  260  via control plane interface  265  to AMF/UPF  264  and user plane interface  263  to SMF  262 . Further, eNB  224  may directly communicate with gNB  222  via the backhaul connection  223 , with or without gNB direct connectivity to the NGC  260 . In some configurations, the New RAN  220  may only have one or more gNBs  222 , while other configurations include one or more of both eNBs  224  and gNBs  222 . Either gNB  222  or eNB  224  may communicate with UEs  204  (e.g., any of the UEs depicted in  FIG. 1 ). The base stations of the New RAN  220  communicate with the AMF-side of the AMF/UPF  264  over the N2 interface and the UPF-side of the AMF/UPF  264  over the N3 interface. 
     The functions of the AMF include registration management, connection management, reachability management, mobility management, lawful interception, transport for session management (SM) messages between the UE  204  and the SMF  262 , transparent proxy services for routing SM messages, access authentication and access authorization, transport for short message service (SMS) messages between the UE  204  and the short message service function (SMSF) (not shown), and security anchor functionality (SEAF). The AMF also interacts with the authentication server function (AUSF) (not shown) and the UE  204 , and receives the intermediate key that was established as a result of the UE  204  authentication process. In the case of authentication based on a UMTS (universal mobile telecommunications system) subscriber identity module (USIM), the AMF retrieves the security material from the AUSF. The functions of the AMF also include security context management (SCM). The SCM receives a key from the SEAF that it uses to derive access-network specific keys. The functionality of the AMF also includes location services management for regulatory services, transport for location services messages between the UE  204  and the location management function (LMF)  270 , as well as between the New RAN  220  and the LMF  270 , evolved packet system (EPS) bearer identifier allocation for interworking with the EPS, and UE  204  mobility event notification. In addition, the AMF also supports functionalities for non-3GPP access networks. 
     Functions of the UPF include acting as an anchor point for intra-/inter-RAT mobility (when applicable), acting as an external protocol data unit (PDU) session point of interconnect to the data network (not shown), providing packet routing and forwarding, packet inspection, user plane policy rule enforcement (e.g., gating, redirection, traffic steering), lawful interception (user plane collection), traffic usage reporting, quality of service (QoS) handling for the user plane (e.g., UL/DL rate enforcement, reflective QoS marking in the DL), UL traffic verification (service data flow (SDF) to QoS flow mapping), transport level packet marking in the UL and DL, DL packet buffering and DL data notification triggering, and sending and forwarding of one or more “end markers” to the source RAN node. 
     The functions of the SMF  262  include session management, UE Internet protocol (IP) address allocation and management, selection and control of user plane functions, configuration of traffic steering at the UPF to route traffic to the proper destination, control of part of policy enforcement and QoS, and downlink data notification. The interface over which the SMF  262  communicates with the AMF-side of the AMF/UPF  264  is referred to as the N11 interface. 
     Another optional aspect may include a LMF  270 , which may be in communication with the NGC  260  to provide location assistance for UEs  204 . The LMF  270  can be implemented as a plurality of separate servers (e.g., physically separate servers, different software modules on a single server, different software modules spread across multiple physical servers, etc.), or alternately may each correspond to a single server. The LMF  270  can be configured to support one or more location services for UEs  204  that can connect to the LMF  270  via the core network, NGC  260 , and/or via the Internet (not illustrated). 
       FIGS. 3A, 3B, and 3C  illustrate several sample components (represented by corresponding blocks) that may be incorporated into a UE  302  (which may correspond to any of the UEs described herein), a TRP  304  (which may correspond to any of the base stations, gNBs, eNBs, cells, etc. described herein), and a network entity  306  (which may correspond to or embody any of the network functions described herein, including the location server  230  and the LMF  270 ) to support the file transmission operations as taught herein. It will be appreciated that these components may be implemented in different types of apparatuses in different implementations (e.g., in an ASIC, in a system-on-chip (SoC), etc.). The illustrated components may also be incorporated into other apparatuses in a communication system. For example, other apparatuses in a system may include components similar to those described to provide similar functionality. Also, a given apparatus may contain one or more of the components. For example, an apparatus may include multiple transceiver components that enable the apparatus to operate on multiple carriers and/or communicate via different technologies. 
     The UE  302  and the TRP  304  each include wireless wide area network (WWAN) transceiver  310  and  350 , respectively, configured to communicate via one or more wireless communication networks (not shown), such as an NR network, an LTE network, a GSM network, and/or the like. The WWAN transceivers  310  and  350  may be connected to one or more antennas  316  and  356 , respectively, for communicating with other network nodes, such as other UEs, access points, base stations (e.g., eNBs, gNBs), etc., via at least one designated RAT (e.g., NR, LTE, GSM, etc.) over a wireless communication medium of interest (e.g., some set of time/frequency resources in a particular frequency spectrum). The WWAN transceivers  310  and  350  may be variously configured for transmitting and encoding signals  318  and  358  (e.g., messages, indications, information, and so on), respectively, and, conversely, for receiving and decoding signals  318  and  358  (e.g., messages, indications, information, pilots, and so on), respectively, in accordance with the designated RAT. Specifically, the transceivers  310  and  350  include one or more transmitters  314  and  354 , respectively, for transmitting and encoding signals  318  and  358 , respectively, and one or more receivers  312  and  352 , respectively, for receiving and decoding signals  318  and  358 , respectively. 
     The UE  302  and the TRP  304  also include, at least in some cases, wireless local area network (WLAN) transceivers  320  and  360 , respectively. The WLAN transceivers  320  and  360  may be connected to one or more antennas  326  and  366 , respectively, for communicating with other network nodes, such as other UEs, access points, base stations, etc., via at least one designated RAT (e.g., WiFi, LTE-D, Bluetooth®, etc.) over a wireless communication medium of interest. The WLAN transceivers  320  and  360  may be variously configured for transmitting and encoding signals  328  and  368  (e.g., messages, indications, information, and so on), respectively, and, conversely, for receiving and decoding signals  328  and  368  (e.g., messages, indications, information, pilots, and so on), respectively, in accordance with the designated RAT. Specifically, the transceivers  320  and  360  include one or more transmitters  324  and  364 , respectively, for transmitting and encoding signals  328  and  368 , respectively, and one or more receivers  322  and  362 , respectively, for receiving and decoding signals  328  and  368 , respectively. 
     Transceiver circuitry including a transmitter and a receiver may comprise an integrated device (e.g., embodied as a transmitter circuit and a receiver circuit of a single communication device) in some implementations, may comprise a separate transmitter device and a separate receiver device in some implementations, or may be embodied in other ways in other implementations. In an aspect, a transmitter may include or be coupled to a plurality of antennas (e.g., antennas  316 ,  326 ,  356 ,  366 ), such as an antenna array, that permits the respective apparatus to perform transmit “beamforming,” as described herein. Similarly, a receiver may include or be coupled to a plurality of antennas (e.g., antennas  316 ,  326 ,  356 ,  366 ), such as an antenna array, that permits the respective apparatus to perform receive beamforming, as described herein. In an aspect, the transmitter and receiver may share the same plurality of antennas (e.g., antennas  316 ,  326 ,  356 ,  366 ), such that the respective apparatus can only receive or transmit at a given time, not both at the same time. A wireless communication device (e.g., one or both of the transceivers  310  and  320  and/or  350  and  360 ) of the apparatuses  302  and/or  304  may also comprise a network listen module (NLM) or the like for performing various measurements. 
     The apparatuses  302  and  304  also include, at least in some cases, satellite positioning systems (SPS) receivers  330  and  370 . The SPS receivers  330  and  370  may be connected to one or more antennas  336  and  376 , respectively, for receiving SPS signals  338  and  378 , respectively, such as global positioning system (GPS) signals, global navigation satellite system (GLONASS) signals, Galileo signals, Beidou signals, Indian Regional Navigation Satellite System (NAVIC), Quasi-Zenith Satellite System (QZSS), etc. The SPS receivers  330  and  370  may comprise any suitable hardware and/or software for receiving and processing SPS signals  338  and  378 , respectively. The SPS receivers  330  and  370  request information and operations as appropriate from the other systems, and performs calculations necessary to determine the apparatus&#39;  302  and  304  positions using measurements obtained by any suitable SPS algorithm. 
     The TRP  304  and the network entity  306  each include at least one network interface  380  and  390  for communicating with other network entities. For example, the network interfaces  380  and  390  (e.g., one or more network access ports) may be configured to communicate with one or more network entities via a wire-based or wireless backhaul connection. In some aspects, the network interfaces  380  and  390  may be implemented as transceivers configured to support wire-based or wireless signal communication. This communication may involve, for example, sending and receiving messages, parameters, and/or other types of information. 
     The apparatuses  302 ,  304 , and  306  also include other components that may be used in conjunction with the operations as disclosed herein. The UE  302  includes processor circuitry implementing a processing system  332  for providing functionality relating to, for example, sounding reference signals (SRS) transmissions as disclosed herein, and for providing other processing functionality. The TRP  304  includes a processing system  384  for providing functionality relating to, for example, SRS configuration and reception as disclosed herein, and for providing other processing functionality. The network entity  306  includes a processing system  394  for providing functionality relating to, for example, SRS configuration as disclosed herein, and for providing other processing functionality. In an aspect, the processing systems  332 ,  384 , and  394  may include, for example, one or more general purpose processors, multi-core processors, ASICs, digital signal processors (DSPs), field programmable gate arrays (FPGA), or other programmable logic devices or processing circuitry. 
     The apparatuses  302 ,  304 , and  306  include memory circuitry implementing memory components  340 ,  386 , and  396  (e.g., each including a memory device), respectively, for maintaining information (e.g., information indicative of reserved resources, thresholds, parameters, and so on). In some cases, the apparatuses  302 ,  304 , and  306  may include RTT measurement reporting components  342 ,  388 , and  398 , respectively. The RTT measurement reporting components  342 ,  388 , and  398  may be hardware circuits that are part of or coupled to the processing systems  332 ,  384 , and  394 , respectively, that, when executed, cause the apparatuses  302 ,  304 , and  306  to perform the functionality described herein. Alternatively, the RTT measurement reporting components  342 ,  388 , and  398  may be memory modules (as shown in  FIGS. 3A-C ) stored in the memory components  340 ,  386 , and  396 , respectively, that, when executed by the processing systems  332 ,  384 , and  394 , cause the apparatuses  302 ,  304 , and  306  to perform the functionality described herein. 
     The UE  302  may include one or more sensors  344  coupled to the processing system  332  to provide movement and/or orientation information that is independent of motion data derived from signals received by the WWAN transceiver  310 , the WLAN transceiver  320 , and/or the SPS receiver  330 . By way of example, the sensor(s)  344  may include an accelerometer (e.g., a micro-electrical mechanical systems (MEMS) device), a gyroscope, a geomagnetic sensor (e.g., a compass), an altimeter (e.g., a barometric pressure altimeter), and/or any other type of movement detection sensor. Moreover, the sensor(s)  344  may include a plurality of different types of devices and combine their outputs in order to provide motion information. For example, the sensor(s)  344  may use a combination of a multi-axis accelerometer and orientation sensors to provide the ability to compute positions in 2D and/or 3D coordinate systems. 
     In addition, the UE  302  includes a user interface  346  for providing indications (e.g., audible and/or visual indications) to a user and/or for receiving user input (e.g., upon user actuation of a sensing device such a keypad, a touch screen, a microphone, and so on). Although not shown, the apparatuses  304  and  306  may also include user interfaces. 
     Referring to the processing system  384  in more detail, in the downlink, IP packets from the network entity  306  may be provided to the processing system  384 . The processing system  384  may implement functionality for an RRC layer, a packet data convergence protocol (PDCP) layer, a radio link control (RLC) layer, and a medium access control (MAC) layer. The processing system  384  may provide RRC layer functionality associated with broadcasting of system information (e.g., master information block (MIB), system information blocks (SIBs)), RRC connection control (e.g., RRC connection paging, RRC connection establishment, RRC connection modification, and RRC connection release), inter-RAT mobility, and measurement configuration for UE measurement reporting; PDCP layer functionality associated with header compression/decompression, security (ciphering, deciphering, integrity protection, integrity verification), and handover support functions; RLC layer functionality associated with the transfer of upper layer packet data units (PDUs), error correction through ARQ, concatenation, segmentation, and reassembly of RLC service data units (SDUs), re-segmentation of RLC data PDUs, and reordering of RLC data PDUs; and MAC layer functionality associated with mapping between logical channels and transport channels, scheduling information reporting, error correction, priority handling, and logical channel prioritization. 
     The transmitter  354  and the receiver(s)  352  may implement Layer- 1  functionality associated with various signal processing functions. Layer- 1 , which includes a physical (PHY) layer, may include error detection on the transport channels, forward error correction (FEC) coding/decoding of the transport channels, interleaving, rate matching, mapping onto physical channels, modulation/demodulation of physical channels, and MIMO antenna processing. The transmitter  354  handles mapping to signal constellations based on various modulation schemes (e.g., binary phase-shift keying (BPSK), quadrature phase-shift keying (QPSK), M-phase-shift keying (M-PSK), M-quadrature amplitude modulation (M-QAM)). The coded and modulated symbols may then be split into parallel streams. Each stream may then be mapped to an orthogonal frequency division multiplexing (OFDM) subcarrier, multiplexed with a reference signal (e.g., pilot) in the time and/or frequency domain, and then combined together using an inverse fast Fourier transform (IFFT) to produce a physical channel carrying a time domain OFDM symbol stream. The OFDM stream is spatially precoded to produce multiple spatial streams. Channel estimates from a channel estimator may be used to determine the coding and modulation scheme, as well as for spatial processing. The channel estimate may be derived from a reference signal and/or channel condition feedback transmitted by the UE  302 . Each spatial stream may then be provided to one or more different antennas  356 . The transmitter  354  may modulate an RF carrier with a respective spatial stream for transmission. 
     At the UE  302 , the receiver(s)  312  receive a signal through its respective antenna(s)  316 . The receiver(s)  312  recover information modulated onto an RF carrier and provides the information to the processing system  332 . The transmitter(s)  314  and the receiver(s)  312  implement Layer- 1  functionality associated with various signal processing functions. The receiver(s)  312  may perform spatial processing on the information to recover any spatial streams destined for the UE  302 . If multiple spatial streams are destined for the UE  302 , they may be combined by the receiver(s)  312  into a single OFDM symbol stream. The receiver(s)  312  then convert the OFDM symbol stream from the time-domain to the frequency domain using a fast Fourier transform (FFT). The frequency domain signal comprises a separate OFDM symbol stream for each subcarrier of the OFDM signal. The symbols on each subcarrier, and the reference signal, are recovered and demodulated by determining the most likely signal constellation points transmitted by the TRP  304 . These soft decisions may be based on channel estimates computed by a channel estimator. The soft decisions are then decoded and de-interleaved to recover the data and control signals that were originally transmitted by the TRP  304  on the physical channel. The data and control signals are then provided to the processing system  332 , which implements Layer- 3  and Layer- 2  functionality. 
     In the UL, the processing system  332  provides demultiplexing between transport and logical channels, packet reassembly, deciphering, header decompression, and control signal processing to recover IP packets from the core network. The processing system  332  is also responsible for error detection. 
     Similar to the functionality described in connection with the DL transmission by the TRP  304 , the processing system  332  provides RRC layer functionality associated with system information (e.g., MIB, SIB s) acquisition, RRC connections, and measurement reporting; PDCP layer functionality associated with header compression/decompression, and security (ciphering, deciphering, integrity protection, integrity verification); RLC layer functionality associated with the transfer of upper layer PDUs, error correction through ARQ, concatenation, segmentation, and reassembly of RLC SDUs, re-segmentation of RLC data PDUs, and reordering of RLC data PDUs; and MAC layer functionality associated with mapping between logical channels and transport channels, multiplexing of MAC SDUs onto transport blocks (TBs), demultiplexing of MAC SDUs from TBs, scheduling information reporting, error correction through HARQ, priority handling, and logical channel prioritization. 
     Channel estimates derived by the channel estimator from a reference signal or feedback transmitted by the TRP  304  may be used by the transmitter(s)  314  to select the appropriate coding and modulation schemes, and to facilitate spatial processing. The spatial streams generated by the transmitter(s)  314  may be provided to different antenna(s)  316 . The transmitter(s)  314  may modulate an RF carrier with a respective spatial stream for transmission. 
     The UL transmission is processed at the TRP  304  in a manner similar to that described in connection with the receiver function at the UE  302 . The receiver(s)  352  receive a signal through its respective antenna(s)  356 . The receiver(s)  352  recover information modulated onto an RF carrier and provides the information to the processing system  384 . 
     In the UL, the processing system  384  provides demultiplexing between transport and logical channels, packet reassembly, deciphering, header decompression, control signal processing to recover IP packets from the UE  302 . IP packets from the processing system  384  may be provided to the core network. The processing system  384  is also responsible for error detection. 
     For convenience, the apparatuses  302 ,  304 , and/or  306  are shown in  FIGS. 3A-C  as including various components that may be configured according to the various examples described herein. It will be appreciated, however, that the illustrated blocks may have different functionality in different designs. 
     The various components of the apparatuses  302 ,  304 , and  306  may communicate with each other over data buses  334 ,  382 , and  392 , respectively. The components of  FIGS. 3A-C  may be implemented in various ways. In some implementations, the components of  FIGS. 3A-C  may be implemented in one or more circuits such as, for example, one or more processors and/or one or more ASICs (which may include one or more processors). Here, each circuit may use and/or incorporate at least one memory component for storing information or executable code used by the circuit to provide this functionality. For example, some or all of the functionality represented by blocks  310  to  346  may be implemented by processor and memory component(s) of the UE  302  (e.g., by execution of appropriate code and/or by appropriate configuration of processor components). Similarly, some or all of the functionality represented by blocks  350  to  388  may be implemented by processor and memory component(s) of the TRP  304  (e.g., by execution of appropriate code and/or by appropriate configuration of processor components). Also, some or all of the functionality represented by blocks  390  to  398  may be implemented by processor and memory component(s) of the network entity  306  (e.g., by execution of appropriate code and/or by appropriate configuration of processor components). For simplicity, various operations, acts, and/or functions are described herein as being performed “by a UE,” “by a base station,” “by a positioning entity,” etc. However, as will be appreciated, such operations, acts, and/or functions may actually be performed by specific components or combinations of components of the UE, base station, positioning entity, etc., such as the processing systems  332 ,  384 ,  394 , the transceivers  310 ,  320 ,  350 , and  360 , the memory components  340 ,  386 , and  396 , the RTT measurement reporting components  342 ,  388 , and  398 , etc. 
       FIG. 4  illustrates an exemplary wireless communications system  400  according to aspects of the disclosure. In the example of  FIG. 4 , a UE  404  (which may correspond to any of the UEs described herein) is attempting to calculate an estimate of its position, or assist another entity (e.g., a base station or core network component, another UE, a location server, a third party application, etc.) to calculate an estimate of its position. The UE  404  may communicate wirelessly with a plurality of base stations  402 - 1 ,  402 - 2 , and  402 - 3  (collectively, base stations  402 , and which may correspond to any of the base stations described herein) using RF signals and standardized protocols for the modulation of the RF signals and the exchange of information packets. By extracting different types of information from the exchanged RF signals, and utilizing the layout of the wireless communications system  400  (i.e., the base stations&#39; locations, geometry, etc.), the UE  404  may determine its position, or assist in the determination of its position, in a predefined reference coordinate system. In an aspect, the UE  404  may specify its position using a two-dimensional coordinate system; however, the aspects disclosed herein are not so limited, and may also be applicable to determining positions using a three-dimensional coordinate system, if the extra dimension is desired. Additionally, while  FIG. 4  illustrates one UE  404  and three base stations  402 , as will be appreciated, there may be more UEs  404  and more base stations  402 . 
     To support position estimates, the base stations  402  may be configured to broadcast reference RF signals (e.g., PRS, NRS, CRS, TRS, CSI-RS, PSS, or SSS, etc.) to UEs  404  in their coverage area to enable a UE  404  to measure characteristics of such reference RF signals. For example, the UE  404  may measure the time of arrival (ToA) of specific reference RF signals (e.g., PRS, NRS, CRS, CSI-RS, etc.) transmitted by at least three different base stations  402 - 1 ,  402 - 2 , and  402 - 3  and may use the RTT positioning method to report these ToAs (and additional information) back to the serving base station  402  or another positioning entity (e.g., location server  230 , LMF  270 ). 
     In an aspect, although described as the UE  404  measuring reference RF signals from a base station  402 , the UE  404  may measure reference RF signals from one of multiple TRPs supported by a base station  402 . Where the UE  404  measures reference RF signals transmitted by a TRP supported by a base station  402 , the at least two other reference RF signals measured by the UE  404  to perform the RTT procedure would be from TRPs supported by base stations  402  different from the first base station  402  and may have good or poor signal strength at the UE  404 . 
     In order to determine the position (x, y) of the UE  404 , the entity determining the position of the UE  404  needs to know the locations of the base stations  402 , which may be represented in a reference coordinate system as (x k , y k ), where k=1, 2, 3 in the example of  FIG. 4 . Where one of the base stations  402  (e.g., the serving base station) or the UE  404  determines the position of the UE  404 , the locations of the involved base stations  402  may be provided to the serving base station  402  or the UE  404  by a location server with knowledge of the network geometry (e.g., location server  230 , LMF  270 ). Alternatively, the location server may determine the position of the UE  404  using the known network geometry. 
     Either the UE  404  or the respective base station  402  may determine the distance  410  (d k , where k=1, 2, 3) between the UE  404  and the respective base station  402 . Specifically, the distance  410 - 1  between the UE  404  and base station  402 - 1  is d 1 , the distance  410 - 2  between the UE  404  and base station  402 - 2  is d 2 , and the distance  410 - 3  between the UE  404  and base station  402 - 3  is d 3 . In an aspect, determining the RTT of signals exchanged between the UE  404  and any base station  402  can be performed and converted to a distance  410  (d k ). As discussed further below, RTT techniques can measure the time between sending a signaling message (e.g., reference RF signals) and receiving a response. These methods may utilize calibration to remove any processing delays. In some environments, it may be assumed that the processing delays for the UE  404  and the base stations  402  are the same. However, such an assumption may not be true in practice. 
     Once each distance  410  is determined, the UE  404 , a base station  402 , or the location server (e.g., location server  230 , LMF  270 ) can solve for the position (x, y) of the UE  404  by using a variety of known geometric techniques, such as, for example, trilateration. From  FIG. 4 , it can be seen that the position of the UE  404  ideally lies at the common intersection of three semicircles, each semicircle being defined by radius d k  and center (x k , y k ), where k=1, 2, 3. 
     In some instances, additional information may be obtained in the form of an angle of arrival (AoA) or angle of departure (AoD) that defines a straight line direction (e.g., which may be in a horizontal plane or in three dimensions) or possibly a range of directions (e.g., for the UE  404  from the location of a base station  402 ). The intersection of the two directions at or near the point (x, y) can provide another estimate of the location for the UE  404 . 
     A position estimate (e.g., for a UE  404 ) may be referred to by other names, such as a location estimate, location, position, position fix, fix, or the like. A position estimate may be geodetic and comprise coordinates (e.g., latitude, longitude, and possibly altitude) or may be civic and comprise a street address, postal address, or some other verbal description of a location. A position estimate may further be defined relative to some other known location or defined in absolute terms (e.g., using latitude, longitude, and possibly altitude). A position estimate may include an expected error or uncertainty (e.g., by including an area or volume within which the location is expected to be included with some specified or default level of confidence). 
       FIG. 5  is an exemplary diagram  500  showing exemplary timings of RTT measurement signals exchanged between a TRP  502  (e.g., any of the base stations, gNBs, cells, etc. described herein) and a UE  504  (e.g., any of the UEs described herein), according to aspects of the disclosure. In the example of  FIG. 5 , the TRP  502  sends an RTT measurement signal  510  (e.g., PRS, NRS, CRS, CSI-RS, etc.) to the UE  504  at time T 1 . The RTT measurement signal  510  has some propagation delay T Prop  as it travels from the TRP  502  to the UE  504 . At time T 2  (the ToA of the RTT measurement signal  510  at the UE  504 ), the UE  504  receives/measures the RTT measurement signal  510 . After some UE processing time, the UE  504  transmits an RTT response signal  520  (e.g., an SRS, UL-PRS) at time T 3 . After the propagation delay T Prop , the TRP  502  receives/measures the RTT response signal  520  from the UE  504  at time T 4  (the ToA of the RTT response signal  520  at the TRP  502 ). 
     In order to identify the ToA (e.g., T 2 ) of an RF signal (e.g., an RTT measurement signal  510 ) transmitted by a given network node, the receiver (e.g., UE  504 ) first jointly processes all the resource elements (REs) on the channel on which the transmitter (e.g., TRP  502 ) is transmitting the RF signal, and performs an inverse Fourier transform to convert the received RF signals to the time domain. The conversion of the received RF signals to the time domain is referred to as estimation of the channel energy response (CER). The CER shows the peaks on the channel over time, and the earliest “significant” peak should therefore correspond to the ToA of the RF signal. Generally, the receiver will use a noise-related quality threshold to filter out spurious local peaks, thereby presumably correctly identifying significant peaks on the channel. For example, the UE  504  may chose a ToA estimate that is the earliest local maximum of the CER that is at least X decibels (dB) higher than the median of the CER and a maximum Y dB lower than the main peak on the channel. The receiver determines the CER for each RF signal from each transmitter in order to determine the ToA of each RF signal from the different transmitters. 
     The RTT response signal  520  may explicitly include the difference between time T 3  and time T 2  (i.e., T Rx→Tx ). Alternatively, it may be derived from the timing advance (TA), i.e., the relative UL/DL frame timing and specification location of UL reference signals. (Note that the TA is usually the RTT between the TRP  502  and the UE  504 , or double the propagation time in one direction.) Using this measurement and the difference between time T 4  and time T 1  (i.e., T Tx→Rx ), the TRP  502  can calculate the distance to the UE  504  as: 
                   d   =         1     2   ⁢   c       ⁢     (       T       T   ⁢   x     →     R   ⁢   x         -     T       R   ⁢   x     →     T   ⁢   x           )       =         1     2   ⁢   c       ⁢     (       T   2     -     T   1       )       +       1     2   ⁢   c       ⁢     (       T   4     -     T   3       )                   (   1   )               
where c is the speed of light.
 
     Note that the UE  504  can perform an RTT procedure with multiple TRPs  502 . However, the RTT procedure does not require synchronization between these TRPs  502 . In the multi-RTT positioning procedure, the basic procedure is repeatedly performed between the UE and multiple TRPs (e.g., base stations gNBs, eNBs, cells, etc.). The basic procedure is as follows:
         1. gNB transmits downlink (DL) reference signal (RS) at time T 1  (also referred to as T gNB,Tx );   2. DL RS arrives at the UE at time T 2  (also referred to as T UE,Rx );   3. UE transmits uplink (UL) RS at time T 3  (also referred to as T UE,Tx );   4. UL RS arrives at the gNB at time T 4  (also referred to as T gNB,Rx ).       

     Positioning reference signal (PRS) is an example of the DL RS and sounding reference signal (SRS) is an example of the UL RS. With the knowledge of (T 4 -T 1 ) and (T 3 -T 2 ), the following equation may be generated: 
     
       
         
           
             
               
                 
                   
                     
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     In conventional wireless networks (e.g., LTE), an E-CID (Enhanced Cell-ID) procedure is defined to determine the UE position. In this procedure, the UE measures its surroundings and provides measurement reports to the network. One measurement report may include measurements results for up to 32 TRPs. For a measured TRP, the measurement results includes:
         UE Rx-Tx      cell ID;   RSRP/RSRQ (reference signal received power/reference signal received quality) for the DL measurement (RRM measurements if available);   SFN (system frame number) of the frame of that cell in which the UE considers the DL measurement to be valid.       

     The parameter UE Rx-Tx  (which will also be referred to as UETimeDiff for purposes of discussion) is defined as T UE,Rx -T UE,Tx  in which T UE,Rx  is a UE receive timing of a downlink (DL) radio frame from the serving cell, and T UE,Tx  is a UE transmit timing of corresponding uplink (UL) radio frame to the serving cell. This is visually presented in  FIG. 6 . As seen, the UETimeDiff is the difference between the transmit timing of uplink frame #i at the UE and the receive timing of downlink frame #i also at the UE. Even though up to 32 cells can be measured, the UETimeDiff is provided only for the UE primary cell. 
     In 5G NR, one measurement report and for a given cell k (not just for the primary cell), the UE will include:
         the UE Rx-Tx,k −T UE,Rx,k −T UE,Tx,k ;   cell ID (or PRS ID) and SRS ID;   SFN of the frame of the serving cell during which the reported measurements is valid;   RSRP/RSRQ for the DL measurement.       

     For example, in the scenario of  FIG. 6 , the measurement report will include the UETimeDiff measurements of multiple cells (e.g., serving gNB 1  and neighbor gNB 2 ). 
     Typically, the UETimeDiffs are measurements of signal on the earliest path, i.e., line of sight (LOS) signals. However, it is not necessarily true that the earliest path is the strongest path. A time of arrival (TOA) estimation accuracy depends on the signal energy received over the shortest radio path, i.e., at or around a first channel tap. In conventional techniques, the energy of later channel taps (e.g., stronger paths) remain unused in the TOA estimation. The stronger path may be determined in various ways according to the various aspects disclosed herein. For example, the stronger path may be the first path that is X dB (e.g., 20 dB) stronger than the earliest path. Alternatively, the stronger path may be the first path that is X dB (e.g., 20 dB) stronger than the earliest path and is within a given time window. In another aspect, the stronger path may be the first path that is stronger that is the strongest path that is at least X nsec away from TOA of the earliest path. In various examples, the time window could be at least K/BW nsec, where K is an integer (e.g., 1, 2, 3, etc.) and BW is the PRS bandwidth or some reference bandwidth. Alternatively, the length X nsec could be related to the reporting granularity of the timing measurements (e.g., equal to the step size, etc.). 
     The aforementioned conventional techniques can be problematic if the earliest path is noisy, at least relative to the signal being transmitted. For example, in uplink transmissions, the UE may be power limited. If the direct path from the UE to the cell is noisy, detecting the LOS signal at the serving or neighbor TRP may be difficult if not impossible. Under such circumstances, attempting to measure the TOA of the earliest path would present challenges. 
     To address such issues associated with conventional measurement techniques, the following observations are made. First, as indicated above, it can be that in some circumstances, a non-direct path (i.e., stronger path) can be stronger than the direct path. That is, energy of the later channel taps can be stronger than the first channel tap. Accordingly, for uplink transmissions from the UE to the TRP, even if the earliest path, i.e., direct path, is too noisy, the strength of a stronger non-direct/non-earliest path UL signals may be such that the uplink transmissions can be reliably detected by the TRP. As noted above, it will be appreciated that the stronger path may be determined in a variety of ways and the examples provided herein are merely illustrative and are not intended to limit the various aspects disclosed herein. 
     A second observation is that the TRP is usually not power limited for the downlink transmission. Accordingly, even if the direct path is too noisy for the UL transmissions from UE, the TRP can transmit DL signals with enough power so that the earliest path is detectable at the UE. Further, the stronger non-direct path should also be detectable at the UE. The UE can calculate the difference, i.e., the offset between the earliest and stronger paths or more generally a stronger path. However, it will be appreciated that the stronger path is not necessarily limited to being the strongest path. 
       FIG. 7  illustrates a diagram showing exemplary steps and timing to determine an RTT of a proposed “robust RTT” procedure. In the multi-RTT positioning procedure, the basic procedure is repeatedly performed between the UE and multiple gNBs (more broadly, TRPs). The robust-RTT procedure is as follows:
         1. gNB transmits DL RS for positioning at T 1 ;   2. UE measures both T 2  (TOA of earliest path) and T 2,S  (TOA of stronger path) of the DL RS;   3. UE transmits UL RS for positioning at T 3 , and also reports UE RS-TX =T 3 -T 2  and Δ S =T 2,S -T 2 ;   4. gNB measures/estimates one or both of T 4  (TOA of earliest path) and T 4,S  (TOA of stronger path).       

     Positioning reference signal (PRS) is an example of the DL RS and sounding reference signal (SRS) is an example of the UL RS. 
     As seen, the UE reports two quantities—the UETimeDiff UE Rs-Tx  as in the conventional baseline RTT procedure. But unlike the baseline RTT procedure, the UE in the proposed procedure also reports Δ s , which is the offset from the earliest to stronger path. If the TRP detects the earliest path, then the TRP can estimate the RTT in the conventional way utilizing equation (2). 
     However, if the TRP does not detect the earliest path or the earliest path is too weak to reliably detect its TOA, then the TRP can estimate the RTT from the TOA T 4,S  of the stronger path and the offset Δ S  as follows: 
     
       
         
           
             
               
                 
                   
                     
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     In equation (3), the quantity (T 4,S -T 1 ) is measured by the TRP and the quantities A S  and (T 3 -T 2 ) are reported from the UE. 
     The proposed procedure is more robust than the conventional baseline RTT procedure to determine the RTT, referred herein as “robust RTT” procedure. In the robust RTT procedure, the measurement on the uplink is more robust since the TRP only has to detect the stronger path—it does NOT have to detect the earliest path. Of course, one assumption is that the difference between the stronger and earliest cluster is the same (or at least similar enough within measurement tolerances) for the DL and the UL (e.g., as in TDD). 
     Following lists some of the options that may be implemented based on the proposed robust RTT procedure. In regards to signaling, the UE may default to and/or requested/instructed to report the offset L. When the UE reports or indicates the additional offset parameter, the TRP can estimate the RTT using the stronger peak of the UL RS. 
     It will be appreciated that both baseline and the robust RTT procedures may be used. Whether to use one or the other may depend on the following (not necessarily exhaustive options):
         On a path loss measurement, or power control command:
           If the UE is power limited on the UL (e.g., at or below UL power threshold), then the robust RTT procedure can be used.   
           Serving TRP may toggle between the baseline and the robust RTT procedures, e.g., for any non-serving TRPs:
           A flag (e.g., a bit) may be used to inform which TRP follows which procedure (baseline (track earliest), robust RTT (track stronger));   
           If the UL bandwidth is small and the DL bandwidth is large, it will be easier for the UE to estimate the earliest path on the DL, but difficult for the TRP to do son on the UL:
           The robust RTT procedure may kick in when the UL RS bandwidth is less than or equal to a UL bandwidth threshold;   
           If the TRP configures the UE to track a signal that is at some X dB higher than the earliest path (i.e., the TRP configures the SDT), the UE may report the offset Δ S  of that signal. If such path does not exist, the UE may simply report the earliest path;   If the TRP sends a timing advance (TA) command to a UE &amp; the UE is configured to use the robust RTT &amp; and the UL RS is used ONLY for positioning purposes &amp; there are no other UL channels adjacent to that UL RS resource:
           Then the UE adjusts the TA command;   Otherwise, the UE transmits the feedback parameters (UETimeDiff, offset) without adjusting the TA command;   The UE may report its capability of whether it is able to do TA adjustment or feedback or both;   
           For each TRP, the reporting of the feedback parameters (UETimeDiff, offset) are reported with same accuracy, e.g., same step size;   UE jointly encodes the feedback parameters (UETimeDiff, offset) and reports one encoded quantity:
           e.g., the UE can report the quantity
 
UE Rx-Tx   +A   s =( T   3   −T   2   +A   S );  (4)
   the TRP can then calculate   
               

     
       
         
           
             
               
                 
                   
                     
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     Note that equation (5) is equivalent to equation (3). Also, in an aspect any of the thresholds—the SD threshold, the SW threshold, the UL power threshold, the UL bandwidth threshold—may be preset and/or dynamically set. 
       FIG. 8  illustrates an exemplary method  800  performed by a UE for providing measurement reports. At block  810 , the UE may receive configuration message, e.g., from a serving TRP notifying the UE of various operational parameters (detailed further below).At block  820 , the UE may receive one or more downlink reference signals (DL RS s) from one or more of the TRPs (e.g., plurality of gNBs). PRSs are examples of the DL RS s. 
       FIG. 9  illustrates an example process performed by the UE to implement block  820 . 
     The UE may repeat the process illustrated in  FIG. 9  for the DL RS received from each TRP. At block  910 , the UE may measure the time of arrival (TOA) T 2  of the earliest path of the DL RS. Therefore, T 2  may also be referred to as the UE earliest reception time. Then n can be said to represent the UE earliest reception time of TRP k. 
     At block  920 , the UE may determine whether the stronger path is to be tracked. It may be determined that the stronger path is to be tracked when any one or more of the following conditions are met:
         UE is preconfigured and/or dynamically configured (e.g., through the configuration message received at block  810 ) to track the stronger path;   Configuration message indicates that the TRP transmitting the DL RS is configured to track the stronger path of the UL RS;   Bandwidth of the UL RS transmitted by the UE is less than or equal to the UL bandwidth threshold; and   UE is power limited on UL transmissions at or below the UL power threshold.       

     If it is determined that the stronger path is to be tracked (Y branch from block  920 ), then at block  930 , the UE may determine whether or not a stronger path is found. In some examples a stronger path will be the stronger path. As the term “stronger” implies, the stronger path is stronger than the earliest path. However, it is possible that there are no other paths that yield a stronger path than the earliest path. Therefore, it may be determined that no stronger path is found. In an aspect, a first non-direct path signal whose strength is greater than the earliest path may be chosen as the stronger path. 
     However, since it can be impractical to wait for a long time to determine whether there are any stronger paths at all, the UE may search for a stronger path within a strength threshold window of time of the earliest path. If one is found, that signal can be chosen as the stronger path. For example, the first non-direct path signal with greater strength found within the strength threshold window may be chosen as the stronger path. Alternatively, a strongest non-path signal with greater strength within the strength threshold window can be chosen. If no such signal is found within the strength window threshold, then it may be determined that no stronger path is found. The strength window threshold may be preconfigured in the UE and/or may be dynamically configured (e.g., through the configuration message received at block  810 ). 
     In some circumstances, it may be desirable to have the strength differential be at least some level, e.g., X dB higher, referred to as the strength differential threshold. Therefore in another aspect, in order for a non-direct path signal to be chosen as the stronger path, it should satisfy:
 
strength( T   Rx,S )&gt;strength( T   Rx )+SDT  (6)
 
     where SDT is the strength differential threshold, which may be preconfigured in the UE and/or may be dynamically configured (e.g., through the configuration message received at block  810 ). 
     Again, since it can be impractical to wait for a long time, the strength differential and the strength window thresholds can be combined. For example, the first non-direct path signal found within the strength threshold window satisfying equation (5) may be chosen as the stronger path. Alternatively, a strongest non-path signal within the strength threshold window satisfying equation (5) can be chosen. If no such signal is found within the strength window threshold, then it may be determined that no stronger path is found. 
     If it is determined that the stronger path is found (Y branch from block  930 ), then at block  940 , the UE may also measure the TOA T 2,S  of the stronger path of the DL RS. Therefore, T 2,S  may also be referred to as the UE stronger reception time. Then T 2,S   k  can be said to represent the UE stronger reception time of TRP k. 
     If it is determined that the stronger path is not to be tracked (N branch from block  920 ) or that the stronger path is not found (N branch from block  930 ), the UE stronger reception time T 2,S  need not be measured. 
     Referring back to  FIG. 8 , at block  830 , the UE may transmit one or more uplink reference signals (UL RSs) to the one or more TRPs to the plurality of DL RSs. SRSs are examples of the UL RSs. Each UL RS may be transmitted at time T 3 . Therefore, T 3  may also be referred to as the UE transmission time. Then T 3   k  can be said to represent the UE transmission time of TRP k. 
     It is contemplated that the UE may receive one or more timing advance (TA) commands from the serving TRP, e.g., in between receiving a DL RS and transmitting a UL RS. If such a TA command is received, the UE may or may not adjust the TA command when transmitting the UL RS in a frame.  FIG. 10  illustrates an example process performed by the UE to implement block  830 . The UE may repeat the process illustrated in  FIG. 10  for each UL RS transmitted. 
     At block  1010 , the UE may determine whether or not a timing advance (TA) command is received, e.g., from the serving TRP. For example, the TA command may be received in between reception of a DL RS and a transmission of a UL RS. That is, the TA command may be received subsequent to T 2  or T 2,S  of one TRP and T 3  of the same TRP or of a different TRP. 
     If the TA command is not received (N branch from block  1010 ), then at block  1040 , the UE may transmit the UL RS with no timing adjustments. On the other hand, if the TA command is received (Y branch from block  1010 ), then at block  1020 , the UE may determine whether all of the following TA adjust conditions are met:
         Track stronger path is in effect;   The UL RS is used ONLY for positioning purpose; and   There are no other UL channels adjacent to that UL RS resource.       

     If any of the TA adjust conditions is not met (N branch from block  1020 ), then the UE may proceed to block  1040  to transmit the UL RS without adjusting the TA command for the UL RS. For example, if the UL RS is used for communication purposes (e.g., the TRP may want to determine what modulation and coding scheme (MCS) to use in the UL and DL channels to exchange data with the UE; the TRP may want to determine/adjust the timing advance to be applied by the UE so that the UL channels from the UE are aligned with the UL channels from other UEs; the TRP may want to decide what numerology to use when communicating with the UE), then the UE may apply the TA command without adjustment for the SRS as well as for the other UL channels regardless of whether or not the SRS is also used for positioning purposes. 
     As another example, if there are other UL channels (e.g., PUCCH, PUSCH, etc.) adjacent to the UL RS resource, then the TA command is not adjusted to the UL RS, i.e., the UL RS as well as other UL channels are advanced in accordance with the TA command. This is because interference can result if a different TA is applied to the UL RS. 
     However, if all of the TA adjust conditions are met (Y branch from block  1020 ), then at block  1030 , the UE may adjust the TA command for the UL RS. In other words, the transmission of the SRS may not be advanced in accordance with the TA command. For example, the TA command may not be applied at all to the UL RS. Then at  1040 , the adjusted UL RS may be transmitted. Note that the TA command may be applied for other UL transmissions without adjustment. 
     Referring back to  FIG. 8 , at block  840 , the UE may generate a measurement report for the one or more TRPs.  FIG. 11  illustrates an example process performed by the UE to implement block  840 . The UE may repeat the process illustrated in  FIG. 11  for the DL RS received from each TRP. For a TRP, at block  1110 , the UE may calculate the UETimeDIFF UE Rs-Tx =T 3 −T 2  intended for the TRP. 
     At  1120 , it may be determined whether or not the stronger path of the DL RS is tracked. If it is determined that the stronger path is tracked, (Y branch from block  1020 ), then at  1130 , the UE may determine the offset Δ S =T 2,S −T 2  of the DL RS. At  1140 , the UE may package the UETimeDIFF and the offset into the measurement report. In one aspect, the UE may package the UETimeDIFF and the offset as separate quantities. Preferably, UETimeDIFF and the offset are packaged with same accuracy or same step size. Alternatively, the UE jointly encode the UETimeDIFF and the offset into one quantity in the measurement report. For example, the UE may package the encoded quantity (T 3 −T 2 +Δ S ) in the measurement report. 
     On the other hand, if it is not determined that the robust RTT approach is in effect (N branch from block  1120 ), then at  1150 , the UE may package the UETimeDIFF into the measurement without packaging the offset. 
     Referring back to  FIG. 8 , at block  850 , the UT may transmit the measurement report. In an aspect, the measurement report may be sent to the serving TRP. It is not necessary to transmit the UETimeDiff and the offset for a TRP together in a single uplink package. While this is possible, it is also possible the split the UETimeDiff and the offset for a TRP in different uplink packages. 
       FIG. 12  illustrates an exemplary method performed by a TRP. In FIG. (e.g., base station, gNB, eNB, etc.) to determine an RTT between the UE and the TRP. The TRP may be a serving TRP or a non-serving TRP. At block  1210 , the TRP may transmit a DL RS to the UE at TRP transmission time T 1 . At block  1220 , the TRP may receive a UL RS from the UE. In block  1220 , the TRP may a TRP earliest reception time T 4  representing a time of arrival (TOA) at the TRP of an earliest path of the UL RS. Alternatively or in addition thereto, the TRP may measure a TRP stronger reception time T 4,s  representing a TOA at the TRP of a stronger path of the UL RS. 
     At block  1230 , the TRP may receive a measurement report from the UE. The measurement may include UETimeDIFF UE Rs-Tx =T 3 −T 2 . T 2  is a UE earliest reception time representing a time of arrival (TOA) at the UE of an earliest path of the DL RS from the TRP, and T 3  is a UE transmission time representing a transmission time at the UE of the UL RS to the TRP. The measurement report may also include an offset Δ S =T 2,S −T 2 , in which T 2,S  is a UE stronger reception time representing a TOA at the UE of a stronger path of the DL RS from the TRP. 
     In an aspect, the UETimeDiff and the offset may be packaged as separate quantities in the measurement report. Alternatively, UETimeDiff and the offset may be packaged as jointly encoded single quantity in the measurement report. 
     At block  1240 , the TRP may determine the RTT between it and the UE based on the 
     TRP earliest reception time T 4  and the measurement. In particular, equation (3) may be applied. At block  1250 , the TRP may send the RTT to a location server (another TRP, E-SMLC, GMLC, LMU, etc.) to determine the UE position. If the TRP itself is the location server, the TRP may receive the RTTs from other TRPs and calculate the UE position. 
       FIG. 13  illustrates an exemplary method  1300  of operating a UE (e.g., any of the UEs described herein), according to aspects of the disclosure. 
     At  1310 , the UE receives one or more DL RSs from one or more TRPs (e.g., TRPs of any of the base stations described herein), for example, as at  820  of  FIG. 8 . In an aspect, operation  1310  may be performed by receiver(s)  312 , processing system  332 , memory component  340 , RTT measurement reporting component  342 , any or all of which may be considered means for performing this operation. 
     At  1320 , the UE transmits one or more UL RSs to the one or more TRPs, for example, as at  830  of  FIG. 8 . In an aspect, operation  1320  may be performed by transmitter(s)  314 , processing system  332 , memory component  340 , RTT measurement reporting component  342 , any or all of which may be considered means for performing this operation. 
     At  1330 , the UE generates a measurement report for the one or more TRPs, for example, as at  840  of  FIG. 8 . In an aspect, operation  1330  may be performed by WWAN transceiver  310 , processing system  332 , memory component  340 , RTT measurement reporting component  342 , any or all of which may be considered means for performing this operation. 
     At  1340 , the UE transmits the measurement report, for example, as at  850  of  FIG. 8 . In an aspect, operation  1340  may be performed by transmitter(s)  314 , processing system  332 , memory component  340 , RTT measurement reporting component  342 , any or all of which may be considered means for performing this operation. 
     In an aspect, the measurement report includes, for at least one TRP of the one or more TRPs, a UE time difference and an offset of the at least one TRP. The UE time difference is a difference of a UE transmission time of the UL RS to the at least one TRP and an earliest reception time representing a time of arrival (TOA) at the UE of an earliest path of the DL RS from the at least one TRP. The offset is a difference of a stronger reception time representing a TOA at the UE of a stronger path of the DL RS from the at least one TRP and the earliest reception time. 
       FIG. 14  illustrates an exemplary method  1400  of operation a TRP (e.g., a TRP of any of the base stations described herein), according to aspects of the disclosure. 
     At  1410 , the TRP transmits a DL RS to a UE (e.g., any of the UEs described herein) at T 1 , for example, as at  1210  of  FIG. 12 . In an aspect, operation  1410  may be performed by transmitter(s)  354 , processing system  384 , memory component  386 , RTT measurement reporting component  388 , any or all of which may be considered means for performing this operation. 
     At  1420 , the TRP receives an UL RS corresponding to the DL RS, for example, as at  1220  of  FIG. 12 . In an aspect, operation  1420  may be performed by receiver(s)  352 , processing system  384 , memory component  386 , RTT measurement reporting component  388 , any or all of which may be considered means for performing this operation. 
     At  1430 , the TRP receives a measurement report from the UE, for example, as at  1230  of  FIG. 12 . In an aspect, operation  1430  may be performed by receiver(s)  352 , processing system  384 , memory component  386 , RTT measurement reporting component  388 , any or all of which may be considered means for performing this operation. 
     In an aspect, the measurement report includes a UE time difference and an offset of the TRP. The UE time difference is a difference of a UE transmission time of the UL RS to the TRP and an earliest reception time representing a time of arrival (TOA) at the UE of an earliest path of the DL RS from the TRP. The offset is a difference of a stronger reception time representing a TOA at the UE of a stronger path of the DL RS from TRP and the earliest reception time. 
       FIG. 15  illustrates an example network node apparatus  1500 , which can serve as a TRP, represented as a series of interrelated functional modules connected by a common bus. Each of the modules may be implemented in hardware or as a combination of hardware and software. For example, the modules may be implemented as any combination of the components of apparatus  304 . A module for transmitting downlink reference signal  1510  may correspond at least in some aspects to, for example, one or more transmitters, such as transmitter(s)  354  in  FIG. 3B , and/or a processing system, such as processing system  384  in  FIG. 3B , optionally in conjunction with memory component  386  and/or RTT measurement reporting component  388 , as discussed herein. A module for receiving uplink reference signal  1520  may correspond at least in some aspects to, for example, one or more receivers, such as receiver(s)  352  in  FIG. 3B  and/or a processing system, such as processing system  384  in  FIG. 3B , optionally in conjunction with memory component  386  and/or RTT measurement reporting component  388 , as discussed herein. A module for receiving measurement report  1530  may correspond at least in some aspects to, for example, one or more receivers, such as receiver(s)  352  in  FIG. 3B  and/or a processing system, such as processing system  384  in  FIG. 3B , optionally in conjunction with memory component  386  and/or RTT measurement reporting component  388 , as discussed herein. An optional module for determining RTT  1540  may correspond at least in some aspects to, for example, a processing system, such as processing system  384  in  FIG. 3B , optionally in conjunction with memory component  386  and/or RTT measurement reporting component  388 , as discussed herein. An optional module for sending RTT  1550  may correspond at least in some aspects to, for example, one or more transmitters, such as transmitter(s)  354  in  FIG. 3B  and/or a processing system, such as processing system  384  in  FIG. 3B , optionally in conjunction with memory component  386  and/or RTT measurement reporting component  388 , as discussed herein. 
       FIG. 16  illustrates an example user equipment apparatus  1600  represented as a series of interrelated functional modules connected by a common bus. Each of the modules may be implemented in hardware or as a combination of hardware and software. For example, the modules may be implemented as any combination of the components of apparatus  302 . An optional module for receiving configuration message  1610  may correspond at least in some aspects to, for example, one or more receivers, such as receiver(s)  312  in  FIG. 3A  and/or a processing system, such as processing system  332  in  FIG. 3A , optionally in conjunction with memory component  340  and/or RTT measurement component  342 , as discussed herein. A module for receiving downlink reference signals  1620  may correspond at least in some aspects to, for example, one or more receivers, such as receiver(s)  312  in  FIG. 3A  and/or a processing system, such as processing system  332  in  FIG. 3A , optionally in conjunction with memory component  340  and/or RTT measurement component  342 , as discussed herein. A module for transmitting uplink reference signals  1630  may correspond at least in some aspects to, for example, one or more transmitters, such as transmitter(s)  314  in  FIG. 3A  and/or a processing system, such as processing system  332  in  FIG. 3A , optionally in conjunction with memory component  340  and/or RTT measurement component  342 , as discussed herein. A module for generating a measurement report  1640  may correspond at least in some aspects to, for example, a communication device, such as WWAN transceiver  310  in  FIG. 3A  and/or a processing system, such as processing system  332  in  FIG. 3A , optionally in conjunction with memory component  340  and/or RTT measurement component  342 , as discussed herein. A module for transmitting a measurement report  1650  may correspond at least in some aspects to, for example, one or more transmitters, such as transmitter(s)  314  in  FIG. 3A  and/or a processing system, such as processing system  332  in  FIG. 3A , optionally in conjunction with memory component  340  and/or RTT measurement component  342 , as discussed herein. 
     The functionality of the modules of  FIGS. 15-16  may be implemented in various ways consistent with the teachings herein. In some designs, the functionality of these modules may be implemented as one or more electrical components. In some designs, the functionality of these blocks may be implemented as a processing system including one or more processor components. In some designs, the functionality of these modules may be implemented using, for example, at least a portion of one or more integrated circuits (e.g., an ASIC). As discussed herein, an integrated circuit may include a processor, software, other related components, or some combination thereof. Thus, the functionality of different modules may be implemented, for example, as different subsets of an integrated circuit, as different subsets of a set of software modules, or a combination thereof. Also, it will be appreciated that a given subset (e.g., of an integrated circuit and/or of a set of software modules) may provide at least a portion of the functionality for more than one module. 
     In addition, the components and functions represented by  FIGS. 15-16 , as well as other components and functions described herein, may be implemented using any suitable means. Such means also may be implemented, at least in part, using corresponding structure as taught herein. For example, the components described above in conjunction with the “module for” components of  FIGS. 15-16  also may correspond to similarly designated “means for” functionality. Thus, in some aspects one or more of such means may be implemented using one or more of processor components, integrated circuits, or other suitable structure as taught herein. 
     Those of skill in the art will appreciate that information and signals may be represented using any of a variety of different technologies and techniques. For example, data, instructions, commands, information, signals, bits, symbols, and chips that may be referenced throughout the above description may be represented by voltages, currents, electromagnetic waves, magnetic fields or particles, optical fields or particles, or any combination thereof. 
     Further, those of skill in the art will appreciate that the various illustrative logical blocks, modules, circuits, and algorithm steps described in connection with the aspects disclosed herein may be implemented as electronic hardware, computer software, or combinations of both. To clearly illustrate this interchangeability of hardware and software, various illustrative components, blocks, modules, circuits, and steps have been described above generally in terms of their functionality. Whether such functionality is implemented as hardware or software depends upon the particular application and design constraints imposed on the overall system. Skilled artisans may implement the described functionality in varying ways for each particular application, but such implementation decisions should not be interpreted as causing a departure from the scope of the present disclosure. 
     The various illustrative logical blocks, modules, and circuits described in connection with the aspects disclosed herein may be implemented or performed with a general purpose processor, a DSP, an ASIC, an FPGA, or other programmable logic device, discrete gate or transistor logic, discrete hardware components, or any combination thereof designed to perform the functions described herein. A general purpose processor may be a microprocessor, but in the alternative, the processor may be any conventional processor, controller, microcontroller, or state machine. A processor may also be implemented as a combination of computing devices, e.g., a combination of a DSP and a microprocessor, a plurality of microprocessors, one or more microprocessors in conjunction with a DSP core, or any other such configuration. 
     The methods, sequences and/or algorithms described in connection with the aspects disclosed herein may be embodied directly in hardware, in a software module executed by a processor, or in a combination of the two. A software module may reside in random access memory (RAM), flash memory, read-only memory (ROM), erasable programmable ROM (EPROM), electrically erasable programmable ROM (EEPROM), registers, hard disk, a removable disk, a CD-ROM, or any other form of storage medium known in the art. An exemplary storage medium is coupled to the processor such that the processor can read information from, and write information to, the storage medium. In the alternative, the storage medium may be integral to the processor. The processor and the storage medium may reside in an ASIC. The ASIC may reside in a user terminal (e.g., UE). In the alternative, the processor and the storage medium may reside as discrete components in a user terminal. 
     In one or more exemplary aspects, the functions described may be implemented in hardware, software, firmware, or any combination thereof. If implemented in software, the functions may be stored on or transmitted over as one or more instructions or code on a computer-readable medium. Computer-readable media includes both computer storage media and communication media including any medium that facilitates transfer of a computer program from one place to another. A storage media may be any available media that can be accessed by a computer. By way of example, and not limitation, such computer-readable media can comprise RAM, ROM, EEPROM, CD-ROM or other optical disk storage, magnetic disk storage or other magnetic storage devices, or any other medium that can be used to carry or store desired program code in the form of instructions or data structures and that can be accessed by a computer. Also, any connection is properly termed a computer-readable medium. For example, if the software is transmitted from a website, server, or other remote source using a coaxial cable, fiber optic cable, twisted pair, digital subscriber line (DSL), or wireless technologies such as infrared, radio, and microwave, then the coaxial cable, fiber optic cable, twisted pair, DSL, or wireless technologies such as infrared, radio, and microwave are included in the definition of medium. Disk and disc, as used herein, includes compact disc (CD), laser disc, optical disc, digital versatile disc (DVD), floppy disk and Blu-ray disc where disks usually reproduce data magnetically, while discs reproduce data optically with lasers. Combinations of the above should also be included within the scope of computer-readable media. 
     While the foregoing disclosure shows illustrative aspects of the disclosure, it should be noted that various changes and modifications could be made herein without departing from the scope of the disclosure as defined by the appended claims. The functions, steps and/or actions of the method claims in accordance with the aspects of the disclosure described herein need not be performed in any particular order. Furthermore, although elements of the disclosure may be described or claimed in the singular, the plural is contemplated unless limitation to the singular is explicitly stated.