Patent Publication Number: US-11662419-B2

Title: On demand positioning reference signals and per band deployment aspects

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     The present application for patent claims the benefit of U.S. Provisional Application No. 63/005,082, entitled “ON DEMAND POSITIONING REFERENCE SIGNALS AND PER BAND DEPLOYMENT ASPECTS,” filed Apr. 3, 2020, assigned to the assignee hereof, and expressly incorporated herein by reference in its entirety. 
    
    
     BACKGROUND OF THE DISCLOSURE 
     1. Field of the Disclosure 
     Aspects of the disclosure relate generally to wireless communications. 
     2. Description of the Related Art 
     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 communications (GSM), etc. 
     A fifth generation (5G) wireless 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. 
     SUMMARY 
     The following presents a simplified summary relating to one or more aspects disclosed herein. Thus, the following summary should not be considered an extensive overview relating to all contemplated aspects, nor should the following summary be considered to identify key or critical elements relating to all contemplated aspects or to delineate the scope associated with any particular aspect. Accordingly, the following summary has the sole purpose to present certain concepts relating to one or more aspects relating to the mechanisms disclosed herein in a simplified form to precede the detailed description presented below. 
     In an aspect, a method of wireless communication performed by a user equipment (UE), includes transmitting a first request for a first set of base stations to transmit first on demand positioning reference signals (PRS) in a first band, measuring the first on demand PRS from the first set of base stations in the first band, measuring periodic PRS from a second set of base stations operating in a second band, and sending, to a positioning entity, positioning measurements of at least the first on demand PRS and the periodic PRS. 
     In an aspect, a UE includes a memory, at least one transceiver, and at least one processor communicatively coupled to the memory and the at least one transceiver, the at least one processor configured to cause the at least one transceiver to transmit a first request for a first set of base stations to transmit first on demand PRS in a first band, measure the first on demand PRS from the first set of base stations in the first band, measure periodic PRS from a second set of base stations operating in a second band, and send, to a positioning entity, positioning measurements of at least the first on demand PRS and the periodic PRS. 
     In an aspect, a UE includes means for transmitting a first request for a first set of base stations to transmit first on demand PRS in a first band, means for measuring the first on demand PRS from the first set of base stations in the first band, means for measuring periodic PRS from a second set of base stations operating in a second band, and means for sending, to a positioning entity, positioning measurements of at least the first on demand PRS and the periodic PRS. 
     In an aspect, a non-transitory computer-readable medium storing computer-executable instructions includes computer-executable instructions comprising at least one instruction instructing a UE to transmit a first request for a first set of base stations to transmit first on demand PRS in a first band, at least one instruction instructing the UE to measure the first on demand PRS from the first set of base stations in the first band, at least one instruction instructing the UE to measure periodic PRS from a second set of base stations operating in a second band, and at least one instruction instructing the UE to send, to a positioning entity, positioning measurements of at least the first on demand PRS and the periodic PRS. 
     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 various aspects of the disclosure and are provided solely for illustration of the aspects and not limitation thereof. 
         FIG.  1    illustrates an example wireless communications system, according to aspects of the disclosure. 
         FIGS.  2 A and  2 B  illustrate example wireless network structures, according to aspects of the disclosure. 
         FIGS.  3 A to  3 C  are simplified block diagrams of several sample aspects of components that may be employed in a user equipment (UE), a base station, and a network entity, respectively, and configured to support communications as taught herein. 
         FIGS.  4 A and  4 B  are diagrams illustrating example frame structures and channels within the frame structures, according to aspects of the disclosure. 
         FIG.  5    is an example call flow between a UE, a serving base station, and a location server, according to aspects of the disclosure. 
         FIG.  6    illustrates an example method of wireless communication, according to aspects of the disclosure. 
     
    
    
     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, consumer asset locating 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 device,” 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 the Institute of Electrical and Electronics Engineers (IEEE) 802.11 specification, 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 next generation eNB (ng-eNB), a New Radio (NR) Node B (also referred to as a gNB or gNodeB), etc. A base station may be used primarily to support wireless access by UEs, including supporting data, voice, and/or signaling connections for the supported UEs. 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 uplink/reverse or downlink/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 (or several cell sectors) 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 radio frequency (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. 
     In some implementations that support positioning of UEs, a base station may not support wireless access by UEs (e.g., may not support data, voice, and/or signaling connections for UEs), but may instead transmit reference signals to UEs to be measured by the UEs, and/or may receive and measure signals transmitted by the UEs. Such a base station may be referred to as a positioning beacon (e.g., when transmitting signals to UEs) and/or as a location measurement unit (e.g., when receiving and measuring signals from UEs). 
     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. 
       FIG.  1    illustrates an example wireless communications system  100 , according to aspects of the disclosure. The wireless communications system  100  (which may also be referred to as a wireless wide area network (WWAN)) may include various base stations  102  (labeled “BS”) 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 and/or ng-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 a 5G core (5GC)) through backhaul links  122 , and through the core network  170  to one or more location servers  172  (e.g., a location management function (LMF) or a secure user plane location (SUPL) location platform (SLP)). The location server(s)  172  may be part of core network  170  or may be external to core network  170 . 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/5GC) 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 geographic 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), a cell global identifier (CGI)) 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 of 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 (SC) base station  102 ′ may have a geographic coverage area  110 ′ that substantially overlaps with the geographic 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 uplink (also referred to as reverse link) transmissions from a UE  104  to a base station  102  and/or downlink (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 downlink and uplink (e.g., more or less carriers may be allocated for downlink than for uplink). 
     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-co-located, 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 co-located. In NR, there are four types of quasi-co-location (QCL) relations. Specifically, a QCL relation of a given type means that certain parameters about a target reference RF signal on a target beam can be derived from information about a source reference RF signal on a source beam. 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 target 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 target 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 target 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 target 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 one or more reference downlink reference signals (e.g., positioning reference signals (PRS), tracking reference signals (TRS), phase tracking reference signal (PTRS), cell-specific reference signals (CRS), channel state information reference signals (CSI-RS), primary synchronization signals (PSS), secondary synchronization signals (SSS), synchronization signal blocks (SSBs), etc.) from a base station. The UE can then form a transmit beam for sending one or more uplink reference signals (e.g., uplink positioning reference signals (UL-PRS), sounding reference signal (SRS), demodulation reference signals (DMRS), PTRS, etc.) 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, FR1 (from 450 to 6000 MHz), FR2 (from 24250 to 52600 MHz), FR3 (above 52600 MHz), and FR4 (between FR1 and FR2). 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., FR1) 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., FR2) 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 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 . 
     In the example of  FIG.  1   , one or more Earth orbiting satellite positioning system (SPS) space vehicles (SVs)  112  (e.g., satellites) may be used as an independent source of location information for any of the illustrated UEs (shown in  FIG.  1    as a single UE  104  for simplicity). A UE  104  may include one or more dedicated SPS receivers specifically designed to receive SPS signals  124  for deriving geo location information from the SVs  112 . An SPS typically includes a system of transmitters (e.g., SVs  112 ) positioned to enable receivers (e.g., UEs  104 ) to determine their location on or above the Earth based, at least in part, on signals (e.g., SPS signals  124 ) received from the transmitters. Such a transmitter typically transmits a signal marked with a repeating pseudo-random noise (PN) code of a set number of chips. While typically located in SVs  112 , transmitters may sometimes be located on ground-based control stations, base stations  102 , and/or other UEs  104 . 
     The use of SPS signals  124  can be augmented by various satellite-based augmentation systems (SBAS) that may be associated with or otherwise enabled for use with one or more global and/or regional navigation satellite systems. For example an SBAS may include an augmentation system(s) that provides integrity information, differential corrections, etc., such as the Wide Area Augmentation System (WAAS), the European Geostationary Navigation Overlay Service (EGNOS), the Multi-functional Satellite Augmentation System (MSAS), the Global Positioning System (GPS) Aided Geo Augmented Navigation or GPS and Geo Augmented Navigation system (GAGAN), and/or the like. Thus, as used herein, an SPS may include any combination of one or more global and/or regional navigation satellite systems and/or augmentation systems, and SPS signals  124  may include SPS, SPS-like, and/or other signals associated with such one or more SPS. 
     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 (referred to as “sidelinks”). In the example of  FIG.  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. 
       FIG.  2 A  illustrates an example wireless network structure  200 . For example, a 5GC  210  (also referred to as a Next Generation Core (NGC)) 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 5GC  210  and specifically to the control plane functions  214  and user plane functions  212 . In an additional configuration, an ng-eNB  224  may also be connected to the 5GC  210  via NG-C  215  to the control plane functions  214  and NG-U  213  to user plane functions  212 . Further, ng-eNB  224  may directly communicate with gNB  222  via a backhaul connection  223 . In some configurations, a Next Generation RAN (NG-RAN)  220  may only have one or more gNBs  222 , while other configurations include one or more of both ng-eNBs  224  and gNBs  222 . Either gNB  222  or ng-eNB  224  may communicate with UEs  204  (e.g., any of the UEs depicted in  FIG.  1   ). Another optional aspect may include location server  230 , which may be in communication with the 5GC  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, 5GC  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. 
       FIG.  2 B  illustrates another example wireless network structure  250 . A 5GC  260  (which may correspond to 5GC  210  in  FIG.  2 A ) can be viewed functionally as control plane functions, provided by an access and mobility management function (AMF)  264 , and user plane functions, provided by a user plane function (UPF)  262 , which operate cooperatively to form the core network (i.e., 5GC  260 ). User plane interface  263  and control plane interface  265  connect the ng-eNB  224  to the 5GC  260  and specifically to UPF  262  and AMF  264 , respectively. In an additional configuration, a gNB  222  may also be connected to the 5GC  260  via control plane interface  265  to AMF  264  and user plane interface  263  to UPF  262 . Further, ng-eNB  224  may directly communicate with gNB  222  via the backhaul connection  223 , with or without gNB direct connectivity to the 5GC  260 . In some configurations, the NG-RAN  220  may only have one or more gNBs  222 , while other configurations include one or more of both ng-eNBs  224  and gNBs  222 . Either gNB  222  or ng-eNB  224  may communicate with UEs  204  (e.g., any of the UEs depicted in  FIG.  1   ). The base stations of the NG-RAN  220  communicate with the AMF  264  over the N2 interface and with the UPF  262  over the N3 interface. 
     The functions of the AMF  264  include registration management, connection management, reachability management, mobility management, lawful interception, transport for session management (SM) messages between the UE  204  and a session management function (SMF)  266 , 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  264  also interacts with an 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  264  retrieves the security material from the AUSF. The functions of the AMF  264  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  264  also includes location services management for regulatory services, transport for location services messages between the UE  204  and an LMF  270  (which acts as a location server  230 ), transport for location services messages between the NG-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  264  also supports functionalities for non-3GPP (Third Generation Partnership Project) access networks. 
     Functions of the UPF  262  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 a 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., uplink/downlink rate enforcement, reflective QoS marking in the downlink), uplink traffic verification (service data flow (SDF) to QoS flow mapping), transport level packet marking in the uplink and downlink, downlink packet buffering and downlink data notification triggering, and sending and forwarding of one or more “end markers” to the source RAN node. The UPF  262  may also support transfer of location services messages over a user plane between the UE  204  and a location server, such as an SLP  272 . 
     The functions of the SMF  266  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  262  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  266  communicates with the AMF  264  is referred to as the N11 interface. 
     Another optional aspect may include an LMF  270 , which may be in communication with the 5GC  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, 5GC  260 , and/or via the Internet (not illustrated). The SLP  272  may support similar functions to the LMF  270 , but whereas the LMF  270  may communicate with the AMF  264 , NG-RAN  220 , and UEs  204  over a control plane (e.g., using interfaces and protocols intended to convey signaling messages and not voice or data), the SLP  272  may communicate with UEs  204  and external clients (not shown in  FIG.  2 B ) over a user plane (e.g., using protocols intended to carry voice and/or data like the transmission control protocol (TCP) and/or IP). 
       FIGS.  3 A,  3 B, and  3 C  illustrate several example components (represented by corresponding blocks) that may be incorporated into a UE  302  (which may correspond to any of the UEs described herein), a base station  304  (which may correspond to any of the base stations 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 base station  304  each include at least one wireless wide area network (WWAN) transceiver  310  and  350 , respectively, providing means for communicating (e.g., means for transmitting, means for receiving, means for measuring, means for tuning, means for refraining from transmitting, etc.) 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 WWAN 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 base station  304  also include, at least in some cases, at least one short-range wireless transceiver  320  and  360 , respectively. The short-range wireless transceivers  320  and  360  may be connected to one or more antennas  326  and  366 , respectively, and provide means for communicating (e.g., means for transmitting, means for receiving, means for measuring, means for tuning, means for refraining from transmitting, etc.) 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®, Zigbee®, Z-Wave®, PC5, dedicated short-range communications (DSRC), wireless access for vehicular environments (WAVE), near-field communication (NFC), etc.) over a wireless communication medium of interest. The short-range wireless 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 short-range wireless 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. As specific examples, the short-range wireless transceivers  320  and  360  may be WiFi transceivers, Bluetooth® transceivers, Zigbee® and/or Z-Wave® transceivers, NFC transceivers, or vehicle-to-vehicle (V2V) and/or vehicle-to-everything (V2X) transceivers. 
     Transceiver circuitry including at least one transmitter and at least one 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 UE  302  and/or the base station  304  may also comprise a network listen module (NLM) or the like for performing various measurements. 
     The UE  302  and the base station  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, and may provide means for receiving and/or measuring 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 positions of the UE  302  and the base station  304  using measurements obtained by any suitable SPS algorithm. 
     The base station  304  and the network entity  306  each include at least one network interfaces  380  and  390 , respectively, providing means for communicating (e.g., means for transmitting, means for receiving, etc.) 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 UE  302 , the base station  304 , and the network entity  306  also include other components that may be used in conjunction with the operations as disclosed herein. The UE  302  includes processor circuitry implementing at least one processor  332  for providing functionality relating to, for example, wireless positioning, and for providing other processing functionality. The base station  304  includes at at least one processor  384  for providing functionality relating to, for example, wireless positioning as disclosed herein, and for providing other processing functionality. The network entity  306  includes at least one processor  394  for providing functionality relating to, for example, wireless positioning as disclosed herein, and for providing other processing functionality. The processors  332 ,  384 , and  394  may therefore provide means for processing, such as means for determining, means for calculating, means for receiving, means for transmitting, means for indicating, etc. In an aspect, the processors  332 ,  384 , and  394  may include, for example, one or more processors, such as one or more general purpose processors, multi-core processors, ASICs, digital signal processors (DSPs), field programmable gate arrays (FPGA), other programmable logic devices or processing circuitry, or various combinations thereof. 
     The UE  302 , the base station  304 , and the network entity  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). The memory components  340 ,  386 , and  396  may therefore provide means for storing, means for retrieving, means for maintaining, etc. In some cases, the UE  302 , the base station  304 , and the network entity  306  may include positioning components  342 ,  388 , and  398 , respectively. The positioning components  342 ,  388 , and  398  may be hardware circuits that are part of or coupled to the processors  332 ,  384 , and  394 , respectively, that, when executed, cause the UE  302 , the base station  304 , and the network entity  306  to perform the functionality described herein. In other aspects, the positioning components  342 ,  388 , and  398  may be external to the processors  332 ,  384 , and  394  (e.g., part of a modem processing system, integrated with another processing system, etc.). Alternatively, the positioning components  342 ,  388 , and  398  may be memory modules stored in the memory components  340 ,  386 , and  396 , respectively, that, when executed by the processors  332 ,  384 , and  394  (or a modem processing system, another processing system, etc.), cause the UE  302 , the base station  304 , and the network entity  306  to perform the functionality described herein.  FIG.  3 A  illustrates possible locations of the positioning component  342 , which may be part of the at least one WWAN transceiver  310 , the memory component  340 , the at least one processor  332 , or any combination thereof, or may be a standalone component.  FIG.  3 B  illustrates possible locations of the positioning component  388 , which may be part of the at least one WWAN transceiver  350 , the memory component  386 , the at least one processor  384 , or any combination thereof, or may be a standalone component.  FIG.  3 C  illustrates possible locations of the positioning component  398 , which may be part of the at least one network interfaces  390 , the memory component  396 , the at least one processor  394 , or any combination thereof, or may be a standalone component. 
     The UE  302  may include one or more sensors  344  coupled to the at least one processor  332  to provide means for sensing or detecting movement and/or orientation information that is independent of motion data derived from signals received by the at least one WWAN transceiver  310 , the at least one short-range wireless 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 two-dimensional (2D) and/or three-dimensional (3D) coordinate systems. 
     In addition, the UE  302  includes a user interface  346  providing means 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 base station  304  and the network entity  306  may also include user interfaces. 
     Referring to the at least one processor  384  in more detail, in the downlink, IP packets from the network entity  306  may be provided to the at least one processor  384 . The at least one processor  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 at least one processor  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 PDUs, error correction through automatic repeat request (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  352  may implement Layer-1 (L1) 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 symbol 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  312  receives a signal through its respective antenna(s)  316 . The receiver  312  recovers information modulated onto an RF carrier and provides the information to the at least one processor  332 . The transmitter  314  and the receiver  312  implement Layer-1 functionality associated with various signal processing functions. The receiver  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  312  into a single OFDM symbol stream. The receiver  312  then converts 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 base station  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 base station  304  on the physical channel. The data and control signals are then provided to the at least one processor  332 , which implements Layer-3 (L3) and Layer-2 (L2) functionality. 
     In the uplink, the at least one processor  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 at least one processor  332  is also responsible for error detection. 
     Similar to the functionality described in connection with the downlink transmission by the base station  304 , the at least one processor  332  provides RRC layer functionality associated with system information (e.g., MIB, SIBs) 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 hybrid automatic repeat request (HARM), priority handling, and logical channel prioritization. 
     Channel estimates derived by the channel estimator from a reference signal or feedback transmitted by the base station  304  may be used by the transmitter  314  to select the appropriate coding and modulation schemes, and to facilitate spatial processing. The spatial streams generated by the transmitter  314  may be provided to different antenna(s)  316 . The transmitter  314  may modulate an RF carrier with a respective spatial stream for transmission. 
     The uplink transmission is processed at the base station  304  in a manner similar to that described in connection with the receiver function at the UE  302 . The receiver  352  receives a signal through its respective antenna(s)  356 . The receiver  352  recovers information modulated onto an RF carrier and provides the information to the at least one processor  384 . 
     In the uplink, the at least one processor  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 at least one processor  384  may be provided to the core network. The at least one processor  384  is also responsible for error detection. 
     For convenience, the UE  302 , the base station  304 , and/or the network entity  306  are shown in  FIGS.  3 A to  3 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 UE  302 , the base station  304 , and the network entity  306  may communicate with each other over data buses  334 ,  382 , and  392 , respectively. The components of  FIGS.  3 A to  3 C  may be implemented in various ways. In some implementations, the components of  FIGS.  3 A to  3 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 base station  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 network 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  302 , base station  304 , network entity  306 , etc., such as the processors  332 ,  384 ,  394 , the transceivers  310 ,  320 ,  350 , and  360 , the memory components  340 ,  386 , and  396 , the positioning components  342 ,  388 , and  398 , etc. 
     Various frame structures may be used to support downlink and uplink transmissions between network nodes (e.g., base stations and UEs).  FIG.  4 A  is a diagram  400  illustrating an example of a downlink frame structure, according to aspects of the disclosure.  FIG.  4 B  is a diagram  430  illustrating an example of channels within the downlink frame structure, according to aspects of the disclosure. Other wireless communications technologies may have different frame structures and/or different channels. 
     LTE, and in some cases NR, utilizes OFDM on the downlink and single-carrier frequency division multiplexing (SC-FDM) on the uplink. Unlike LTE, however, NR has an option to use OFDM on the uplink as well. OFDM and SC-FDM partition the system bandwidth into multiple (K) orthogonal subcarriers, which are also commonly referred to as tones, bins, etc. Each subcarrier may be modulated with data. In general, modulation symbols are sent in the frequency domain with OFDM and in the time domain with SC-FDM. The spacing between adjacent subcarriers may be fixed, and the total number of subcarriers (K) may be dependent on the system bandwidth. For example, the spacing of the subcarriers may be 15 kilohertz (kHz) and the minimum resource allocation (resource block) may be 12 subcarriers (or 180 kHz). Consequently, the nominal FFT size may be equal to 128, 256, 512, 1024, or 2048 for system bandwidth of 1.25, 2.5, 5, 10, or 20 megahertz (MHz), respectively. The system bandwidth may also be partitioned into subbands. For example, a subband may cover 1.08 MHz (i.e.,  6  resource blocks), and there may be 1, 2, 4, 8, or 16 subbands for system bandwidth of 1.25, 2.5, 5, 10, or 20 MHz, respectively. 
     LTE supports a single numerology (subcarrier spacing (SCS), symbol length, etc.). In contrast, NR may support multiple numerologies (μ), for example, subcarrier spacings of 15 kHz (μ=0), 30 kHz (μ=1), 60 kHz (μ=2), 120 kHz (μ=3), and 240 kHz (μ=4) or greater may be available. In each subcarrier spacing, there are 14 symbols per slot. For 15 kHz SCS (μ=0), there is one slot per subframe, 10 slots per frame, the slot duration is 1 millisecond (ms), the symbol duration is 66.7 microseconds (μs), and the maximum nominal system bandwidth (in MHz) with a 4K FFT size is 50. For 30 kHz SCS (μ=1), there are two slots per subframe, 20 slots per frame, the slot duration is 0.5 ms, the symbol duration is 33.3 μs, and the maximum nominal system bandwidth (in MHz) with a 4K FFT size is 100. For 60 kHz SCS (μ=2), there are four slots per subframe, 40 slots per frame, the slot duration is 0.25 ms, the symbol duration is 16.7 μs, and the maximum nominal system bandwidth (in MHz) with a 4K FFT size is 200. For 120 kHz SCS (μ=3), there are eight slots per subframe, 80 slots per frame, the slot duration is 0.125 ms, the symbol duration is 8.33 μs, and the maximum nominal system bandwidth (in MHz) with a 4K FFT size is 400. For 240 kHz SCS (μ=4), there are 16 slots per subframe, 160 slots per frame, the slot duration is 0.0625 ms, the symbol duration is 4.17 μs, and the maximum nominal system bandwidth (in MHz) with a 4K FFT size is 800. 
     In the example of  FIGS.  4 A and  4 B , a numerology of 15 kHz is used. Thus, in the time domain, a 10 ms frame is divided into 10 equally sized subframes of 1 ms each, and each subframe includes one time slot. In  FIGS.  4 A and  4 B , time is represented horizontally (on the X axis) with time increasing from left to right, while frequency is represented vertically (on the Y axis) with frequency increasing (or decreasing) from bottom to top. 
     A resource grid may be used to represent time slots, each time slot including one or more time-concurrent resource blocks (RBs) (also referred to as physical RBs (PRBs)) in the frequency domain. The resource grid is further divided into multiple resource elements (REs). An RE may correspond to one symbol length in the time domain and one subcarrier in the frequency domain. In the numerology of  FIGS.  4 A and  4 B , for a normal cyclic prefix, an RB may contain 12 consecutive subcarriers in the frequency domain and seven consecutive symbols in the time domain, for a total of 84 REs. For an extended cyclic prefix, an RB may contain 12 consecutive subcarriers in the frequency domain and six consecutive symbols in the time domain, for a total of 72 REs. The number of bits carried by each RE depends on the modulation scheme. 
     Some of the REs carry downlink reference (pilot) signals (DL-RS). The DL-RS may include PRS, TRS, PTRS, CRS, CSI-RS, DMRS, PSS, SSS, SSB, etc.  FIG.  4 A  illustrates example locations of REs carrying PRS (labeled “R”). 
     A collection of resource elements (REs) that are used for transmission of PRS is referred to as a “PRS resource.” The collection of resource elements can span multiple PRBs in the frequency domain and ‘N’ (such as 1 or more) consecutive symbol(s) within a slot in the time domain. In a given OFDM symbol in the time domain, a PRS resource occupies consecutive PRBs in the frequency domain. 
     The transmission of a PRS resource within a given PRB has a particular comb size (also referred to as the “comb density”). A comb size ‘N’ represents the subcarrier spacing (or frequency/tone spacing) within each symbol of a PRS resource configuration. 
     Specifically, for a comb size ‘N,’ PRS are transmitted in every Nth subcarrier of a symbol of a PRB. For example, for comb-4, for each symbol of the PRS resource configuration, REs corresponding to every fourth subcarrier (such as subcarriers 0, 4, 8) are used to transmit PRS of the PRS resource. Currently, comb sizes of comb-2, comb-4, comb-6, and comb-12 are supported for DL-PRS.  FIG.  4 A  illustrates an example PRS resource configuration for comb-6 (which spans six symbols). That is, the locations of the shaded REs (labeled “R”) indicate a comb-6 PRS resource configuration. 
     Currently, a DL-PRS resource may span 2, 4, 6, or 12 consecutive symbols within a slot with a fully frequency-domain staggered pattern. A DL-PRS resource can be configured in any higher layer configured downlink or flexible (FL) symbol of a slot. There may be a constant energy per resource element (EPRE) for all REs of a given DL-PRS resource. The following are the frequency offsets from symbol to symbol for comb sizes 2, 4, 6, and 12 over 2, 4, 6, and 12 symbols. 2-symbol comb-2: {0, 1}; 4-symbol comb-2: {0, 1, 0, 1}; 6-symbol comb-2: {0, 1, 0, 1, 0, 1}; 12-symbol comb-2: {0, 1, 0, 1, 0, 1, 0, 1, 0, 1, 0, 1}; 4-symbol comb-4: {0, 2, 1, 3}; 12-symbol comb-4: {0, 2, 1, 3, 0, 2, 1, 3, 0, 2, 1, 3}; 6-symbol comb-6: {0, 3, 1, 4, 2, 5}; 12-symbol comb-6: {0, 3, 1, 4, 2, 5, 0, 3, 1, 4, 2, 5}; and 12-symbol comb-12: {0, 6, 3, 9, 1, 7, 4, 10, 2, 8, 5, 11}. 
     A “PRS resource set” is a set of PRS resources used for the transmission of PRS signals, where each PRS resource has a PRS resource ID. In addition, the PRS resources in a PRS resource set are associated with the same TRP. A PRS resource set is identified by a PRS resource set ID and is associated with a particular TRP (identified by a TRP ID). In addition, the PRS resources in a PRS resource set have the same periodicity, a common muting pattern configuration, and the same repetition factor (such as “PRS-ResourceRepetitionFactor”) across slots. The periodicity is the time from the first repetition of the first PRS resource of a first PRS instance to the same first repetition of the same first PRS resource of the next PRS instance. The periodicity may have a length selected from 2{circumflex over ( )}μ*{4, 5, 8, 10, 16, 20, 32, 40, 64, 80, 160, 320, 640, 1280, 2560, 5120, 10240} slots, with μ=0, 1, 2, 3. The repetition factor may have a length selected from {1, 2, 4, 6, 8, 16, 32} slots. 
     A PRS resource ID in a PRS resource set is associated with a single beam (or beam ID) transmitted from a single TRP (where a TRP may transmit one or more beams). That is, each PRS resource of a PRS resource set may be transmitted on a different beam, and as such, a “PRS resource,” or simply “resource,” also can be referred to as a “beam.” Note that this does not have any implications on whether the TRPs and the beams on which PRS are transmitted are known to the UE. 
     A “PRS instance” or “PRS occasion” is one instance of a periodically repeated time window (such as a group of one or more consecutive slots) where PRS are expected to be transmitted. A PRS occasion also may be referred to as a “PRS positioning occasion,” a “PRS positioning instance, a “positioning occasion,” “a positioning instance,” a “positioning repetition,” or simply an “occasion,” an “instance,” or a “repetition.” 
     A “positioning frequency layer” (also referred to simply as a “frequency layer”) is a collection of one or more PRS resource sets across one or more TRPs that have the same values for certain parameters. Specifically, the collection of PRS resource sets has the same subcarrier spacing and cyclic prefix (CP) type (meaning all numerologies supported for the PDSCH are also supported for PRS), the same Point A, the same value of the downlink PRS bandwidth, the same start PRB (and center frequency), and the same comb-size. The Point A parameter takes the value of the parameter “ARFCN-ValueNR” (where “ARFCN” stands for “absolute radio-frequency channel number”) and is an identifier/code that specifies a pair of physical radio channel used for transmission and reception. The downlink PRS bandwidth may have a granularity of four PRBs, with a minimum of 24 PRBs and a maximum of 272 PRBs. Currently, up to four frequency layers have been defined, and up to two PRS resource sets may be configured per TRP per frequency layer. 
     The concept of a frequency layer is somewhat like the concept of component carriers and bandwidth parts (BWPs), but different in that component carriers and BWPs are used by one base station (or a macro cell base station and a small cell base station) to transmit data channels, while frequency layers are used by several (usually three or more) base stations to transmit PRS. A UE may indicate the number of frequency layers it can support when it sends the network its positioning capabilities, such as during an LTE positioning protocol (LPP) session. For example, a UE may indicate whether it can support one or four positioning frequency layers. 
     Note that the terms “positioning reference signal” and “PRS” generally refer to specific reference signals that are used for positioning in NR and LTE systems. However, as used herein, the terms “positioning reference signal” and “PRS” may also refer to any type of reference signal that can be used for positioning, such as but not limited to, PRS as defined in LTE and NR, TRS, PTRS, CRS, CSI-RS, DMRS, PSS, SSS, SSB, SRS, UL-PRS, etc. In addition, the terms “positioning reference signal” and “PRS” may refer to downlink or uplink positioning reference signals, unless otherwise indicated by the context. If needed to further distinguish the type of PRS, a downlink positioning reference signal may be referred to as a “DL-PRS,” and an uplink positioning reference signal (e.g., an SRS-for-positioning, PTRS) may be referred to as an “UL-PRS.” In addition, for signals that may be transmitted in both the uplink and downlink (e.g., DMRS, PTRS), the signals may be prepended with “UL” or “DL” to distinguish the direction. For example, “UL-DMRS” may be differentiated from “DL-DMRS.” 
     PRS, and other types of positioning reference signals, are used for a number of cellular network-based positioning technologies, including downlink-based, uplink-based, and downlink-and-uplink-based positioning methods. Downlink-based positioning methods include observed time difference of arrival (OTDOA) in LTE, downlink time difference of arrival (DL-TDOA) in NR, and downlink angle-of-departure (DL-AoD) in NR. In an OTDOA or DL-TDOA positioning procedure, a UE measures the differences between the times of arrival (ToAs) of reference signals (e.g., PRS, TRS, CSI-RS, SSB, etc.) received from pairs of base stations, referred to as reference signal time difference (RSTD) or time difference of arrival (TDOA) measurements, and reports them to a positioning entity. More specifically, the UE receives the identifiers (IDs) of a reference base station (e.g., a serving base station) and multiple non-reference base stations in assistance data. The UE then measures the RSTD between the reference base station and each of the non-reference base stations. Based on the known locations of the involved base stations and the RSTD measurements, the positioning entity can estimate the UE&#39;s location. 
     For DL-AoD positioning, the positioning entity uses a beam report from the UE of received signal strength measurements of multiple downlink transmit beams to determine the angle(s) between the UE and the transmitting base station(s). The positioning entity can then estimate the location of the UE based on the determined angle(s) and the known location(s) of the transmitting base station(s). 
     Uplink-based positioning methods include uplink time difference of arrival (UL-TDOA) and uplink angle-of-arrival (UL-AoA). UL-TDOA is similar to DL-TDOA, but is based on uplink reference signals (e.g., SRS) transmitted by the UE. For UL-AoA positioning, one or more base stations measure the received signal strength of one or more uplink reference signals (e.g., SRS) received from a UE on one or more uplink receive beams. The positioning entity uses the signal strength measurements and the angle(s) of the receive beam(s) to determine the angle(s) between the UE and the base station(s). Based on the determined angle(s) and the known location(s) of the base station(s), the positioning entity can then estimate the location of the UE. 
     Downlink-and-uplink-based positioning methods include enhanced cell-ID (E-CID) positioning and multi-round-trip-time (RTT) positioning (also referred to as “multi-cell RTT”). In an RTT procedure, an initiator (a base station or a UE) transmits an RTT measurement signal (e.g., a PRS or SRS) to a responder (a UE or base station), which transmits an RTT response signal (e.g., an SRS or PRS) back to the initiator. The RTT response signal includes the difference between the ToA of the RTT measurement signal and the transmission time of the RTT response signal, referred to as the reception-to-transmission (Rx-Tx) time difference. The initiator calculates the difference between the transmission time of the RTT measurement signal and the ToA of the RTT response signal, referred to as the transmission-to-reception (Tx-Rx) time difference. The propagation time (also referred to as the “time of flight”) between the initiator and the responder can be calculated from the Tx-Rx and Rx-Tx time differences. Based on the propagation time and the known speed of light, the distance between the initiator and the responder can be determined. For multi-RTT positioning, a UE performs an RTT procedure with multiple base stations to enable its location to be triangulated based on the known locations of the base stations. RTT and multi-RTT methods can be combined with other positioning techniques, such as UL-AoA and DL-AoD, to improve location accuracy. 
     The E-CID positioning method is based on radio resource management (RRM) measurements. In E-CID, the UE reports the serving cell ID, the timing advance (TA), and the identifiers, estimated timing, and signal strength of detected neighbor base stations. The location of the UE is then estimated based on this information and the known locations of the base station(s). 
     To assist positioning operations, a location server (e.g., location server  230 , LMF  270 , SLP  272 ) may provide assistance data to the UE. For example, the assistance data may include identifiers of the base stations (or the cells/TRPs of the base stations) from which to measure reference signals, the reference signal configuration parameters (e.g., the number of consecutive positioning subframes, periodicity of positioning subframes, muting sequence, frequency hopping sequence, reference signal identifier, reference signal bandwidth, etc.), and/or other parameters applicable to the particular positioning method. Alternatively, the assistance data may originate directly from the base stations themselves (e.g., in periodically broadcasted overhead messages, etc.). in some cases, the UE may be able to detect neighbor network nodes itself without the use of assistance data. 
     In the case of an OTDOA or DL-TDOA positioning procedure, the assistance data may further include an expected RSTD value and an associated uncertainty, or search window, around the expected RSTD. In some cases, the value range of the expected RSTD may be +/−500 microseconds (μs). In some cases, when any of the resources used for the positioning measurement are in FR1, the value range for the uncertainty of the expected RSTD may be +/−32 μs. In other cases, when all of the resources used for the positioning measurement(s) are in FR2, the value range for the uncertainty of the expected RSTD may be +/−8 μs. 
     A location estimate may be referred to by other names, such as a position estimate, location, position, position fix, fix, or the like. A location 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 location 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 location 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). 
     The downlink PRS transmitted for the above-described positioning procedures can be transmitted periodically or on demand. “On demand” PRS transmission means that PRS are only transmitted when there is a request for PRS to be transmitted, as opposed to TRPs in the network periodically transmitting PRS regardless of whether there are any ongoing positioning sessions. The on demand PRS may themselves be periodic within a predefined time period (e.g., during the positioning session), semi-persistent, or aperiodic. As will be appreciated, the use of on demand PRS transmission reduces PRS overhead. In some cases, on demand PRS transmission may be requested by a UE, such as for a UE-based positioning procedure (in which the UE estimates its own location) or a UE-requested positioning procedure (in which the UE requests the network to estimate the UE&#39;s location). The UE may send a request to receive DL-PRS from and/or transmit UL-PRS to each base station involved in the positioning procedure, or send the request to its serving base station or the location server, which then forwards the request to the involved base stations. In other cases, on demand PRS transmission may be requested by the network (e.g., location server  230 , LMF  270 , SLP  272 ), such as for a UE-assisted positioning procedure (in which the network estimates the UE&#39;s location, either of its own initiative or on request from the UE or another entity). In this case, the location server can send the request to the involved base stations. 
     Network operators may cover a geographic area by deploying an “anchor” set of base stations (e.g., eNBs, ng-eNBs, gNBs) over the whole area in one frequency band, and additional base stations (e.g., ng-eNBS, gNBs) over subsets of the geographic area in one or more other frequency bands. For example, the additional base stations may have more capabilities than the anchor set of base stations, and the network operator may gradually phase them in based on market needs. 
     The present disclosure provides techniques for using a first frequency “band” for periodically broadcasted PRS and one or more additional frequency “bands” for on-demand PRS. More specifically, during a given positioning procedure, a UE may receive periodic PRS in one band and on demand PRS in one or more other bands. Note that the term “band,” as used herein, refers to some generic block of frequency, such as a frequency range (e.g., FR1, FR2, etc.), a frequency band within a frequency range, a component carrier, or a positioning frequency layer. As such, periodic PRS would be transmitted in a first frequency range, a first frequency band, a first component carrier, or a first frequency layer, and on demand PRS would be transmitted in one or more different frequency ranges, one or more different frequency bands, one or more different component carriers, or one or more different frequency layers. 
     A UE can indicate its capability to operate on multiple bands, and the location server (e.g., location server  230 , LMF  270 , SLP  272 ) may configure assistance information for those bands. For UE-based positioning, the assistance information may include the locations of the involved base stations (i.e., the base stations configured to transmit PRS to the UE), from which the UE may infer differences in deployment densities across bands (i.e., the bands on which it is capable of operating). That is, since the UE receives the locations of the involved base stations and the bands they use for transmitting PRS, the UE can determine the number and geographic distribution of the base stations transmitting PRS on each band. 
     For UE-assisted positioning, the locations of the base stations are not included in the assistance information. However, the UE may infer their locations based on a PRS search in the bands it can support. For example, the UE may detect more PRS in a first band in which it can operate than in a second band. Alternatively, the assistance information may include coarse level locations of the involved base stations. For example, the assistance information may indicate that there are more base stations operating in a first band compared to a second band. Whether for UE-based or UE-assisted positioning, the PRS configuration received from the location server may indicate that on demand PRS is only supported in certain bands. 
     For on demand PRS transmission, the UE can send a PRS request (i.e., a request to transmit UL-PRS or receive DL-PRS) to the base stations involved in the positioning procedure via RRC signaling, MAC control elements (MAC-CEs), or uplink control information (UCI). Alternatively, the UE may send a PRS request to its serving base station or the location server (e.g., location server  230 , LMF  270 , SLP  272 ) identifying the base stations from which it wants to receive PRS. In turn, the location server (or serving base station) can forward the request to the identified base stations. Where the location server is located in the core network (e.g., 5GC  210 , 5GC  260 ), the UE can send the request via RRC signaling or LPP signaling. Where the location server is located in the RAN (e.g., NG-RAN  220 ), such as where the location server is co-located with one or more base stations, the UE may send the request using either UE-to-base station signaling or UE-to-core network signaling (e.g., RRC). 
     Where the UE sends a PRS request to each involved base station, the band (e.g., frequency range, component carrier, BWP, frequency layer, etc.) on which the request is conveyed from the UE to the base station may indicate the band on which the on demand PRS should be transmitted. Thus, for example, if a request is transmitted in FR2, it indicates that the base station should transmit PRS in FR2. Likewise, if a request is transmitted on a particular component carrier, it indicates that the base station should transmit PRS on that component carrier. If the request is transmitted in a particular BWP, it indicates that the base station should transmit PRS on the frequency layer corresponding to that BWP. 
     Alternatively, the PRS request can include a band identifier. For example, based on the UE&#39;s knowledge of the deployment density of base stations in different bands, as described above, the UE can indicate one or more preferred bands for the on demand PRS. 
     Thus, during a given positioning procedure, a UE may receive periodic PRS in one band, and in addition, receive on demand PRS in one or more other bands (whether requested by the UE or the locations server). In an aspect, the on demand PRS may be used to supplement the periodic PRS. More specifically, in addition to the periodic PRS a UE may be measuring, the UE can request on demand PRS from a specific base station (or a specific set of base stations) based on its positioning needs. For example, the UE may request PRS from one or more base stations of specific heights in order to compute a 3D location. This may be based on the UE&#39;s prior height estimate (e.g., from its barometer) and may be requested to achieve good (e.g., above a threshold) geometric dilution of precision (GDOP). (GDOP specifies error propagation as a mathematical effect of navigation satellite geometry on positional measurement precision.) In this way, the UE can calculate a 2D estimate of its location using periodic PRS from a first set of base stations operating in a first band, and calculate a 3D estimate of its location by incorporating measurements of on demand PRS from one or more sets of base stations operating in one or more other bands. 
     As another example, a UE may be measuring periodic PRS from a first set of base stations operating in a first band that are all located to one or two sides of the UE. To improve the resulting location estimate, the UE may identify one or more base stations operating in one or more other bands that are on an opposite side of the UE from the first set of base stations, and request on demand PRS from those base stations. In that way, the UE will receive and measure PRS from base stations surrounding the UE. As will be appreciated, measuring PRS from base stations that surround the UE will provide a better location estimate of the UE than will measuring PRS from base stations that are only on one or two sides of the UE. 
     In an aspect, a UE may request on-demand PRS in a second band after determining that it cannot receive/measure the periodic PRS transmitted in a first band. 
     Upon measuring the on demand (and periodic) PRS on the first (and second) bands, the UE may report/send the measurements to a positioning entity. For UE-based positioning, the positioning entity may be a positioning engine on the UE (e.g., positioning component  342 ). For UE-assisted positioning, the positioning entity may be a location server (e.g., location server  230 , LMF  270 , SLP  272 ), a positioning engine at the serving base station, a third-party server or application, or the like. The measurements can be reported separately or in the same measurement report, depending on various factors. The factors may include, for example, the report configuration (whether the UE is configured to consolidate the measurements into one report or send independent reports), the periodicity of the on demand and periodic PRS, the measurement requirements (e.g., RSTD based on PRS from two separate positioning frequency layers), and/or the like. 
     For downlink-and-uplink-based positioning sessions (e.g., RTT), the UE may transmit SRS in response to reception of PRS. In general, the on demand PRS on the second band depends on the positioning method being performed on the first band. For example, if an RTT positioning procedure is being performed on the first band, then it would to be on demand RTT (meaning both downlink and uplink PRS) on the second band. Because the periodic SRS and the on demand SRS are located on two different bands, the UE will likely not be able to transmit them at the same time. Therefore, the UE may only transmit the on demand group. However, the Rx-Tx time difference measurement for the RTT positioning procedure on both bands could be consolidated into one report. 
     Accordingly, for positioning involving SRS, the general procedure is the same. That is, the UE requests the location server for on demand PRS and the location server configures the requested PRS. For DL-PRS, the on demand configuration is received from the location server via LPP, whereas for SRS, the configuration is received from the serving cell. The location server will coordinate the PRS transmission and reception across the involved gNBs. 
       FIG.  5    is an example call flow  500  between a UE  504  (e.g., any of the UEs described herein), a serving base station (BS)  502  (e.g., any of the base stations described herein), and a location server  570  (e.g., location server  230 , LMF  270 , SLP  272 ), according to aspects of the disclosure. 
     At stage  505 , the UE  504  sends a request for on demand PRS to the location server  570 . At  510 , the location server  570  identifies/selects candidate sources (e.g., base stations) to transmit on demand PRS. The candidate sources may be selected based on their GDOP relative to the UE  504 , their availability to transmit on demand PRS, and/or the like. At  515 , the location server sends an on demand PRS configuration and scheduling to the base station  502 . At  520 , the location server  570  or the base station  502  sends the on demand PRS configuration and scheduling to the UE  504 . At  525 , the location server  570  or the base station  502  triggers the UE  504  to measure and report the on demand PRS. At  530 , the base station  502  transmits on demand PRS to the UE  504 , if the base station  502  is one of the on demand PRS sources. At  535 , the UE  504  measures the on demand PRS received from the on demand PRS sources, as well as the periodic PRS if available. At  540 , for UE-assisted positioning, the UE  504  reports the measurements of the on demand and periodic PRS to the location server  570 . Alternatively, for UE-based positioning, the UE  504  would calculate an estimate of its location (not shown). 
       FIG.  6    illustrates an example method  600  of wireless communication, according to aspects of the disclosure. In an aspect, the method  600  may be performed by a UE, such as any of the UEs described herein. 
     At  610 , the UE transmits a first request for a first set of base stations to transmit first on demand PRS in a first band. In an aspect, operation  610  may be performed by the at least one WWAN transceiver  310 , the at least one processor  332 , memory component  340 , and/or positioning component  342 , any or all of which may be considered means for performing this operation. 
     At  620 , the UE measures the first on demand PRS from the first set of base stations in the first band. In an aspect, operation  620  may be performed by the at least one WWAN transceiver  310 , the at least one processor  332 , memory component  340 , and/or positioning component  342 , any or all of which may be considered means for performing this operation. 
     At  630 , the UE measures periodic PRS from a second set of base stations operating in a second band (different from the first band). In an aspect, operation  630  may be performed by the at least one WWAN transceiver  310 , the at least one processor  332 , memory component  340 , and/or positioning component  342 , any or all of which may be considered means for performing this operation. 
     At  640 , the UE sends, to a positioning entity (e.g., a positioning engine at the UE (e.g., positioning component  342 ), a location server, a serving base station), positioning measurements (e.g., ToAs, RSTDs, etc.) of at least the first on demand PRS and the periodic PRS. In an aspect, operation  640  may be performed by the at least one WWAN transceiver  310 , the at least one processor  332 , memory component  340 , and/or positioning component  342 , any or all of which may be considered means for performing this operation. 
     As will be appreciated, technical advantages of the method  600  include enabling a UE to measure more PRS from more base stations, thereby improving positioning performance, reducing the use of system resources, permitting the reuse of other (non-on demand) bands, and reducing power consumption (as the on demand PRS may be transmitted in a band with less power efficiency). 
     In the detailed description above it can be seen that different features are grouped together in examples. This manner of disclosure should not be understood as an intention that the example clauses have more features than are explicitly mentioned in each clause. Rather, the various aspects of the disclosure may include fewer than all features of an individual example clause disclosed. Therefore, the following clauses should hereby be deemed to be incorporated in the description, wherein each clause by itself can stand as a separate example. Although each dependent clause can refer in the clauses to a specific combination with one of the other clauses, the aspect(s) of that dependent clause are not limited to the specific combination. It will be appreciated that other example clauses can also include a combination of the dependent clause aspect(s) with the subject matter of any other dependent clause or independent clause or a combination of any feature with other dependent and independent clauses. The various aspects disclosed herein expressly include these combinations, unless it is explicitly expressed or can be readily inferred that a specific combination is not intended (e.g., contradictory aspects, such as defining an element as both an insulator and a conductor). Furthermore, it is also intended that aspects of a clause can be included in any other independent clause, even if the clause is not directly dependent on the independent clause. 
     Implementation examples are described in the following numbered clauses: 
     Clause 1. A method of wireless communication performed by a user equipment (UE), comprising: transmitting a first request for a first set of base stations to transmit first on demand positioning reference signals (PRS) in a first band; measuring the first on demand PRS from the first set of base stations in the first band; measuring periodic PRS from a second set of base stations operating in a second band; and enabling a positioning entity to calculate a location of the UE based on positioning measurements of at least the first on demand PRS and the periodic PRS. 
     Clause 2. The method of clause 1, further comprising: transmitting, to a location server, a capability message indicating that the UE can support operation on at least the first band and the second band. 
     Clause 3. The method of clause 2, further comprising: receiving, from the location server, assistance information for at least the first set of base stations and the second set of base stations. 
     Clause 4. The method of clause 3, wherein the assistance information includes locations of at least the first set of base stations and the second set of base stations. 
     Clause 5. The method of any of clauses 3 to 4, wherein the assistance information indicates at least a number of the first set of base stations operating in the first band and a number of the second set of base stations operating in the second band. 
     Clause 6. The method of any of clauses 1 to 5, further comprising: determining at least a number of the first set of base stations operating in the first band and a number of the second set of base stations operating in the second band based on detecting at least the first on demand PRS and the periodic PRS. 
     Clause 7. The method of clause 6, further comprising: determining a number of a third set of base stations capable of transmitting second on demand PRS in a third band. 
     Clause 8. The method of clause 7, wherein the UE transmits the first request to the first set of base stations based on the number of the first set of base stations compared to the number of the third set of base stations. 
     Clause 9. The method of any of clauses 1 to 8, further comprising: receiving an indication that only the first band supports on demand PRS. 
     Clause 10. The method of any of clauses 1 to 9, wherein: the first request is transmitted on the first band, and the first request being transmitted on the first band indicates that the first request is for the first set of base stations to transmit the first on demand PRS in the first band. 
     Clause 11. The method of any of clauses 1 to 10, wherein the first request includes an identifier of the first band. 
     Clause 12. The method of any of clauses 1 to 11, wherein the UE transmits the first request for the first set of base stations to transmit the first on demand PRS in the first band based on a positioning need not satisfied by the periodic PRS transmitted by the second set of base stations. 
     Clause 13. The method of any of clauses 1 to 12, further comprising: transmitting a second request for a third set of base stations to transmit second on demand PRS in a third band; and measuring the second on demand PRS from the third set of base stations in the third band, wherein enabling the positioning entity to calculate the location of the UE is further based on positioning measurements of the second on demand PRS. 
     Clause 14. The method of any of clauses 1 to 13, wherein the UE transmits the first request to each of the first set of base stations. 
     Clause 15. The method of any of clauses 1 to 14, wherein: the UE transmits the first request to a location server or a serving base station, and the first request is forwarded by the location server or the serving base station to each of the first set of base stations. 
     Clause 16. The method of any of clauses 1 to 15, wherein: the first band comprises a first frequency range, a first frequency band, a first component carrier, or a first positioning frequency layer, and the second band comprises a second frequency range, a second frequency band, a second component carrier, or a second positioning frequency layer. 
     Clause 17. The method of any of clauses 1 to 16, wherein: the positioning entity comprises the UE, and enabling the positioning entity to calculate the location of the UE comprises the UE calculating the location of the UE based on the positioning measurements of at least the first on demand PRS and the periodic PRS. 
     Clause 18. The method of any of clauses 1 to 17, wherein: the positioning entity comprises a location server, or a serving base station, and enabling the positioning entity to calculate the location of the UE comprises the UE transmitting the positioning measurements of at least the first on demand PRS and the periodic PRS to the positioning entity. 
     Clause 19. An apparatus comprising a memory and at least one processor communicatively coupled to the memory, the memory and the at least one processor configured to perform a method according to any of clauses 1 to 18. 
     Clause 20. An apparatus comprising means for performing a method according to any of clauses 1 to 18. 
     Clause 21. A non-transitory computer-readable medium storing computer-executable instructions, the computer-executable comprising at least one instruction for causing a computer or processor to perform a method according to any of clauses 1 to 18. 
     Additional implementation examples are described in the following numbered clauses: 
     Clause 1. A method of wireless communication performed by a user equipment (UE), comprising: transmitting a first request for a first set of base stations to transmit first on demand positioning reference signals (PRS) in a first band; measuring the first on demand PRS from the first set of base stations in the first band; measuring periodic PRS from a second set of base stations operating in a second band; and sending, to a positioning entity, positioning measurements of at least the first on demand PRS and the periodic PRS. 
     Clause 2. The method of clause 1, further comprising: transmitting, to a location server, a capability message indicating that the UE can support operation on at least the first band and the second band. 
     Clause 3. The method of clause 2, further comprising: receiving, from the location server, assistance information for at least the first set of base stations and the second set of base stations. 
     Clause 4. The method of clause 3, wherein the assistance information includes locations of at least the first set of base stations and the second set of base stations. 
     Clause 5. The method of any of clauses 3 to 4, wherein the assistance information indicates at least a number of the first set of base stations operating in the first band and a number of the second set of base stations operating in the second band. 
     Clause 6. The method of any of clauses 1 to 5, further comprising: determining at least a number of the first set of base stations operating in the first band and a number of the second set of base stations operating in the second band based on detecting at least the first on demand PRS and the periodic PRS. 
     Clause 7. The method of clause 6, further comprising: determining a number of a third set of base stations capable of transmitting second on demand PRS in a third band. 
     Clause 8. The method of clause 7, wherein the UE transmits the first request to the first set of base stations based on the number of the first set of base stations compared to the number of the third set of base stations. 
     Clause 9. The method of any of clauses 1 to 8, further comprising: receiving an indication that only the first band supports on demand PRS. 
     Clause 10. The method of any of clauses 1 to 9, wherein: the first request is transmitted on the first band, and the first request being transmitted on the first band indicates that the first request is for the first set of base stations to transmit the first on demand PRS in the first band. 
     Clause 11. The method of any of clauses 1 to 9, wherein the first request is transmitted on the second band. 
     Clause 12. The method of any of clauses 1 to 11, wherein the first request includes an identifier of the first band. 
     Clause 13. The method of any of clauses 1 to 12, wherein the UE transmits the first request for the first set of base stations to transmit the first on demand PRS in the first band based on a positioning need not satisfied by the periodic PRS transmitted by the second set of base stations. 
     Clause 14. The method of clause 13, wherein the positioning need is based on a geometric dilution of precision (GDOP) threshold. 
     Clause 15. The method of any of clauses 1 to 14, further comprising: transmitting a second request for a third set of base stations to transmit second on demand PRS in a third band; measuring the second on demand PRS from the third set of base stations in the third band; and sending, to the positioning entity, positioning measurements of the second on demand PRS. 
     Clause 16. The method of any of clauses 1 to 15, wherein the UE transmits the first request to each of the first set of base stations. 
     Clause 17. The method of any of clauses 1 to 15, wherein: the UE transmits the first request to a location server or a serving base station, and the first request is sent by the location server or the serving base station to each of the first set of base stations. 
     Clause 18. The method of any of clauses 1 to 17, wherein: the first band comprises a first frequency range, a first frequency band, a first component carrier, or a first positioning frequency layer, and the second band comprises a second frequency range, a second frequency band, a second component carrier, or a second positioning frequency layer. 
     Clause 19. The method of any of clauses 1 to 18, wherein: the positioning entity comprises a positioning engine at the UE, and the method further comprises calculating a location of the UE based on the positioning measurements of at least the first on demand PRS and the periodic PRS. 
     Clause 20. The method of any of clauses 1 to 18, wherein the positioning entity comprises a location server or a serving base station. 
     Clause 21. An apparatus comprising a memory and at least one processor communicatively coupled to the memory, the memory and the at least one processor configured to perform a method according to any of clauses 1 to 20. 
     Clause 22. An apparatus comprising means for performing a method according to any of clauses 1 to 20. 
     Clause 23. A non-transitory computer-readable medium storing computer-executable instructions, the computer-executable comprising at least one instruction for causing a computer or processor to perform a method according to any of clauses 1 to 20. 
     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 digital signal processor (DSP), an ASIC, a field-programmable gate array (FPGA), or other programmable logic device, discrete gate or transistor logic, discrete hardware components, or any combination thereof designed to perform the functions described herein. A general-purpose processor may be a microprocessor, but in the alternative, the processor may be any conventional processor, controller, microcontroller, or state machine. A processor may also be implemented as a combination of computing devices, for example, 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 example 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 example 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.