BACKGROUND

[0001] The role of today's mobile devices— e.g., smart phones, mobile tablets, and wearable computing devices— has expanded dramatically as these devices have proliferated. People do far more on their mobile devices than just make phone calls or access the Internet. New and useful applications for mobile devices are being developed at rapid pace, and many of these applications use location-detection services to perform tasks. These devices communicate through radio waves over dedicated and varying frequencies or dedicated segments of the electromagnetic spectrum. The ability to estimate the relative distance between mobile devices is important for a number of wireless device applications that require location awareness.

[0002] Global Positioning System (GPS) solutions do not perform well indoors and provide somewhat weak location-detection precision. Another location-detection service being deployed is Wi-Fi fingerprint, but this technique uses a Received Signal Strength Indication (RSSI) that provides low spatial resolution. An additional inconvenience for Wi-Fi fingerprint technology is the need for a previous calibration phase, which must be performed whenever the physical topology changes significantly. Moreover, hardware- implemented solutions, such as the manipulation of physical layer (PHY) signal properties— e.g., through signal phases of antennas and round-trip time ends— require all new hardware to be developed or managed. Location-detection services should focus on procedures that enhance accuracy beyond the RSSI barrier and then can operate effectively indoors without having to reconfigure complex PHY layers.

[0003] If location-detection services use contention-based wireless technologies (e.g., Wi-Fi), performance degradation occurs in dense deployment scenarios due to the many nodes vying or transmitting for limited frequency bandwidth. For example, a large number of mobile devices in the same geographical area may have to compete to gain access to one or more radio frequency (RF) channels.

SUMMARY

[0004] The disclosed examples are described in detail below with reference to the accompanying drawing figures listed below. The below Summary is provided to illustrate some examples disclosed herein, and is not meant to necessarily limit all examples to any particular configuration or sequence of operations. [0005] Some examples are directed to performing location detection of mobile computing devices in an area using bulk fine timing measurement (BFTM) timing messages. In some examples, a scheduling mobile computing device assembles and transmits a BFTM allocation message that dictates when a group of mobile computing devices in the area are to transmit BFTM timing messages. The responding mobile computing devices then generate the BFTM timing messages and transmit the generated BFTM timing messages at the scheduled times. The BFTM timing messages may include frames that indicate the times of arrival (TO As), times of departure (TODs), or propagation timing estimates (PTEs) of BFTM timing messages from the other responding computing devices, thereby piggybacking the communication of such timing and propagation information in the BFTM timing message.

BRIEF DESCRIPTION OF THE DRAWINGS

[0006] The disclosed examples are described in detail below with reference to the accompanying drawing figures listed below:

[0007] FIG. 1 is a block diagram illustrating an example of a computing device configured to perform location-detections services.

[0008] FIG. 2 illustrates a block diagram of mobile computing devices communicating BFTM messages.

[0009] FIG. 3 A illustrates an exemplary BFTM allocation message.

[0010] FIG. 3B illustrates an exemplary BFTM timing message.

[0011] FIG. 4A is a timing diagram showing various mobile computing devices communicating different timing measurement messages at given times.

[0012] FIG. 4B is a timing diagram showing various mobile computing devices communicating different timing measurement messages at given times.

[0013] FIG. 4C is a timing diagram showing various mobile computing devices communicating different timing measurement messages at given times.

[0014] FIG. 5 is a flow chart diagram illustrating a work flow for generating a BFTM allocation message.

[0015] FIG. 6 is a flow chart diagram illustrating a work flow for generating a BFTM allocation message.

[0016] FIG. 7 is a flow chart diagram illustrating a work flow for generating a BFTM timing message.

[0017] Corresponding reference characters indicate corresponding parts throughout the drawings. DETAILED DESCRIPTION

[0018] The IEEE 802.11 standard (otherwise known as Wi-Fi) provides some mechanisms to determine the locations of mobile devices using a "fine timing measurement" (FTM) procedure. But the Wi-Fi FTM procedures are very signal-intensive, demanding numerous transmissions to be carried out across somewhat limited wireless frequencies. Consequently, conventional Wi-Fi FTM is not scalable to accommodate location services indoors for large number of mobile computing devices. More specifically, the Wi-Fi fine timing measure requires a sending station to transmit a sender "time of delivery" (TODsnd) to a receiving station at time Tl . The receiving station must then determine a "time of arrival" (TOArcv) at time T2 and transmit the TOA and a time of acknowledgment (T- ACKrcv) back to the sending station at time T3. The sending station assigns its own TOA (i.e., TOAsnd) at time T4 when the sending station receives TOArcv and T-ACKrcv from the receiving station. The sending station can then compute the propagation delay between the two station— and consequently locate the receiving station relative to the sending station— based on the four different times: Tl, T2, T3, and T4.

[0019] This technique requires several messages and timing parameters to be passed back and forth, cluttering up radio frequencies in large areas with many different mobile devices. The current Wi-Fi fine timing measurement technique cannot facilitate location services for large numbers of mobile devices. The number of message exchanges (M) for performing a complete graph of timing measurements among any given number of stations (n) in geographical proximity can be shown by the following Equation 1 :

M = 2 *— ^- = 2 * n * (n - l) (1)

(n-2)! ^J '

[0020] As shown in Equation 1 , the number of messages quadratically varies based on the number of stations sending FTM messages. With only a finite bandwidth of RF frequencies to transmit messages across in a given area, either the number of stations must be reduced or the number of messages. Examples disclosed herein help reduce the latter by batching TOAs and TODs that would normally be included in multiple FTM messages into a single BFTM message.

[0021] Examples disclosed herein are directed to systems, devices, methods, and computer-storage memory for determining mobile computing device locations through transmission of various BFTM messages that include different timing or propagation parameters. In some examples, a scheduling mobile computing device assembles and transmits a BFTM allocation message that dictates when a group of mobile computing devices in the area are to transmit BFTM timing messages. The responding mobile computing devices then generate the BFTM timing messages and transmit the generated BFTM timing messages at the scheduled times. The BFTM timing messages may include frames that indicate TOAs, TODs, or PTEs of BFTM timing messages from the other responding computing devices. Communicating these timing and propagation parameters of other mobile computing devices in the BFTM timing message greatly reduces the number of messages needed to be transmitted between the devices in order to determine their locations.

[0022] In some of the disclosed examples, mobile computing devices generate, transmit, and use a "BFTM allocation message," which includes various message frames, to multiple other mobile computing devices within a particular area. In some examples, the message frames of the BFTM allocation message include a TOD indicative of the time the BFTM allocation message is transmitted; a designation of a number of other mobile computing devices (e.g., station B, station C, and so on); an allocation of a contention-free time period where at least a subset of the other of the mobile computing devices will transmit BFTM or FTM timing messages; a scheduling order for a subset of the mobile computing devices to transmit in a particular order (e.g., station B transmits at time T2, station C transmits at time T3, station D transmits at time T4, and so forth). Additional or alternative information may be included in the BFTM allocation message, including the frame elements disclosed herein and depicted in the accompanying drawings.

[0023] In some of the disclosed examples, mobile computing devices generate, transmit, and use a "BFTM timing message," which includes message frames, during the allocated time in a contention-free period and according to the scheduling order indicated by the BFTM allocation message. In some examples, the message frames of the BFTM timing message include a TOD indicative of the time the BFTM timing message is transmitted; multiple TOAs, including the TOA of the BFTM allocation message and TOAs of previously received FTM or BFTM timing or allocation messages from other mobile computing devices; and one or more propagation timing estimates corresponding to the propagation time of messages from the other mobile computing devices (e.g., messages station B received from C, D, and E) or from the mobile computing device sending the BFTM allocation message (e.g., BFTM allocation message received by station B from station A).

[0024] The BFTM timing messages may include multiple TOAs related to messages received from other mobile computing devices. For example, mobile device A may generate a BFTM allocation message with an assigned TOD to mobile device B, and mobile device B may respond back with a BFTM timing message that includes its own TOD, the TOA of the message from mobile device A, and TO As of previously received messages from other computing devices (e.g., devices C, D, E, and beyond).

[0025] Batching these additional TOAs of the messages received by mobile device

B from the other mobile devices into the BFTM timing message back to mobile device A reduces the need for mobile device A to separately communicate with the other mobile devices, which, when compounded across multiple devices dramatically reduces the above quadric relationship of messages (M) to devices (n) experienced in the aforesaid FTM procedure to the following relation shown in Equation 2:

M = (2 * n) - 1 (2)

[0026] As shown in Equation 2, the number of messages varies linearly— instead of quadratically— with the number of devices, providing a scalable model for rendering indoor location services to accommodate far more mobile devices than conventional FTM location procedures.

[0027] Reducing the number of messages being exchanged reduces processor, memory, and transmission loads of today's mobile computing devices during location detection. It also moves devices away from having to GPS, line-of-sight, or Wi-Fi fingerprint and more complicated hardware-specific (e.g., PHY) configurations. Additionally, the BFTM messages and procedures disclosed herein provide increased reliability for location services, and enhance the user experience; whereas, older technologies typically can only locate devices within a range of 3m. Moreover, the exchange of BFTM messages may be conducted indoors and do not require unobstructed lines of sight from satellites, as required by GPS.

[0028] Throughout this disclosure, the terms "mobile computing device" and

"station" are used interchangeably. One skilled in the art will understand and appreciate that a "station," mobile computing device (e.g., a smart phone, a mobile tablet, a wearable device, Wi-Fi terminal, etc.) may be referred to simply as a station. Additionally, this disclosure generally references "timing measurement messages," which may include BFTM timing messages or standard FTM messages. The former refers to the specific BFTM timing messages disclosed herein that include batched TOAs from multiple mobile computing devices, TODs, propagation time estimates, or a combination thereof. And the latter includes standard FTM messages, such as the messages and procedures described in the forthcoming 802.1REV-mc standard (to be called 802.11 -2016[2]). [0029] Having generally provided an overview of some of the disclosed examples, attention is drawn to the accompanying drawings to further illustrate some additional details. The illustrated configurations and operational sequences are provided for to aid the reader in understanding some aspects of the disclosed examples. The accompanying figures are not meant to limit all examples, and thus some examples may include different components, devices, or sequences of operations while not departing from the scope of the disclosed examples discussed herein. In other words, some examples may be embodied or may function in different ways than those shown.

[0030] FIG. 1 is a block diagram illustrating an example of a mobile computing device 100 configured to perform location-detection services in accordance with some examples disclosed herein. The mobile computing device 100 includes a processor 102, a transceiver 104, a clock 106, input/output (I/O) ports 108, I/O components 110, and a memory area 112. The memory area 112 stores machine-executable instructions and data that include an operating system 114, various applications 116, times of delivery (TODs) 118 and times of arrival (TO As) 120 for BFTM and FTM messages (both BFTM allocation and/or BFTM timing), propagation estimates 122, a BFTM component 124, BFTM allocation messages 126, BFTM timing messages 128, and a device location component 130. The mobile computing device 100 may communicate across a public, private, or hybrid network 130. The depicted mobile computing device 100 is but one example of a suitable computing environment and is not intended to suggest any limitation as to the scope of use or functionality of the disclosed examples. Alternative or additional components may be used in other examples.

[0031] The mobile computing device 100 may take the form of a mobile computing device or any other portable device. In some examples, the mobile computing device 100 may be a mobile phone, laptop, tablet, computing pad, netbook, gaming device, electronic kiosk, wearable device (which may include a natural user interface), portable media player, or other type of computing device that uses touchpads or touch screens. The mobile computing device 100 may also include less portable devices such as desktop personal computers, kiosks, tabletop devices, industrial control devices, wireless charging stations, gaming consoles, servers, electric automobile charging stations, control systems, and the like. Additionally, the mobile computing device 100 may represent a group of processors or other mobile computing devices 100.

[0032] The processor 102 may include one or more processing units that are programmed to execute computer-executable instructions for implementing aspects of the disclosure. The instructions may be performed by the processor 102 or by multiple processors within the mobile computing device 100, or performed by a processor 102 external to the mobile computing device 100. In some examples, the operations illustrated in the accompanying FIGS. 5 and 6 may be implemented as software instructions encoded on a computer-readable medium, in hardware programmed or designed to perform the operations, or both. Moreover, in some examples, the processor 102 represents an implementation of analog techniques to perform the operations described herein. For example, the operations may be performed by an analog computing device and/or a digital computing device, or the operations may be implemented by a system on a chip (SoC) or other circuitry (e.g., a plurality of interconnected, electrically conductive elements). Further still, the processor 102 may operate in a virtualized environment, operating across one or more other computing devices or servers.

[0033] The transceiver 104 is an antenna capable of transmitting and receiving RF signals. The clock 106 provides a clock signal. I/O ports 108 allow mobile computing device 100 to be logically coupled to other devices including I/O components 110— some of which may be built into the mobile computing device 100— that present, record, receive, or otherwise capture data from a user of the mobile computing device 100 or the surrounding environment. Example I/O components 110 include, without limitation, a speaker, a sound card, a camera, a microphone, a vibration motor, an accelerometer, a joystick, a scanner, a printer, a wireless communication module (e.g., Bluetooth®, radio frequency, etc.), global positioning system (GPS) hardware, a photoreceptive light sensor, or other chipsets and circuitry for capturing information related to the user or the user's environment.

[0034] The memory area 112 includes any quantity of computer-storage media associated with or accessible by the mobile computing device 100. The memory area 112 may be internal to the computing device 100 (as shown in FIG. 1), external to the mobile computing device 100 (not shown), or both (not shown). Examples of memory in the memory area 112 include, without limitation, random access memory (RAM); read only memory (ROM); electronically erasable programmable read only memory (EEPROM); flash memory or other memory technologies; CDROM, digital versatile disks (DVDs) or other optical or holographic media; magnetic cassettes, magnetic tape, magnetic disk storage or other magnetic storage devices; memory wired into an analog computing device; or any other medium for encoding desired information and be accessed by the mobile computing device 100. Such memory may also take the form of volatile and/or nonvolatile memory; may be removable, non-removable, or a combination thereof; and may include various hardware devices (e.g., solid-state memory, hard drives, optical-disc drives, etc.). For the purposes of this disclosure, however, "computer storage media" does not include carrier waves or propagating signaling.

[0035] The operating system 114 is executed by the processor 106 and controls operational aspects of the mobile computing device 100. The applications 116, when executed by the processor 102, operate to perform software or hardware functions on the computing device 100, some of which may require location detection. Examples of applications 224 include, without limitation, mail application programs, web browsers, text editors, spreadsheet programs, calendar application programs, gaming programs, address book application programs, messaging programs, media applications, location-based services, search programs, mobile applications, and the like. The applications 112 may communicate with counterpart applications 112 or services on other mobile computing devices 100, such as web services accessible via a network.

[0036] The mobile computing device 100 may communicate over network 130. Examples of computer networks 132 include, without limitation, a wireless network, landline, cable line, fiber-optic line, local area network (LAN), wide area network (WAN), or the like. The network 132 may also comprise subsystems that transfer data between servers or mobile computing devices 100. For example, the network 132 may also include a point-to-point connection, the Internet, an Ethernet, a backplane bus, an electrical bus, a neural network, or other internal system.

[0037] To communicate across the network 132, the mobile computing device 100 may also include a network interface card and/or computer-executable instructions (e.g., a driver) for operating a network interface card that provides access to the network. Communication between the mobile computing device 100 and other devices over the network may occur using any protocol or mechanism over any wired or wireless connection. In some examples, the communications interface is operable with short-range communication technologies such as by using near-field communication (NFC) tags, Bluetooth® tags, or the like. Examples of network transfer protocols include, for example but without limitation, the hypertext transfer protocol (HTTP), file transfer protocol (FTP), simple object access protocol (SOAP), or the like. Examples are not limited to any particular communication protocol, message language, or scripting language, as one skilled in the art will appreciate that different languages and protocols may be used to interact with distributed applications. [0038] The TODs 118 refer to the "times of delivery" that BFTM allocation messages 126 and BFTM timing messages 128 are transmitted from the mobile computing devices 100. BFTM allocation messages 126 and BFTM timing messages 128, which are described in more detail below and examples are given in FIGS. 3 A-3B, represent messages that are wirelessly transmitted (e.g., via Wi-Fi™, Bluetooth®, ZigBee®, Long-Term Evolution (LTE), or some other messaging protocol) that include message frames indicating the various disclosed TOD, TO A, device address, message duration, and other information used by the techniques disclosed herein to locate the mobile computing devices 100 within a given area. As mentioned above, the BFTM allocation message 126 may include a TOD indicative of the time the BFTM allocation message 126 is transmitted; a designation of a number of other mobile computing devices 100 (e.g., station B, station C, and so on); an allocation of a contention-free time period where at least a subset of the other of the mobile computing devices 100 will transmit BFTM timing messages 126; a scheduling order for a subset of the mobile computing devices to transmit in a pre-defined order (e.g., station B transmits at time T2, station C transmits at time T3, station D transmits at time T4, and so forth).

[0039] The TO As 120 refer to the "times of arrival" of given BFTM allocation messages 126, BFTM timing messages 128, and/or FTM messages. The TOAs 120 stored on one mobile computing device 100 may include the times associated with messages the mobile computing device 100 actually receives as well as well as times that messages were received by other mobile computing devices 100 that are transmitting BFTM timing messages 128. For example, if station D received a BFTM timing message 128 from station B at time T3, station D may transmit a corresponding TOA and TOD of this BFTM timing message 128 (referenced as TOABD and TODBD) in subsequently transmitted BFTM timing messages 128. These subsequently transmitted BFTM timing messages 128 may then be received by stations A, B, C, and E, which may each include the TOABD and TODBD timing parameters in their own BFTM timing messages 128.

[0040] The BFTM allocation messages 126 and the BFTM timing messages 128 are timing measurement messages generated by the BFTM message component 130 for communication to other mobile computing devices 100. As mentioned above, the BFTM allocation message may include a TOD indicative of the time the BFTM allocation message is transmitted; a designation of a number of other mobile computing devices (e.g., station B, station C, and so on); an allocation of a contention-free time period where at least a subset of the other of the mobile computing devices will transmit BFTM or FTM timing messages; a scheduling order for a subset of the mobile computing devices to transmit in a pre-defined order (e.g., station B transmits at time T2, station C transmits at time T3, station D transmits at time T4, and so forth).

[0041] The BFTM timing message 128 may include a TOD indicative of the time the BFTM timing message 128 was or is transmitted; multiple TOAs, including the TO A of the BFTM allocation message 126 and TOAs of previously received FTM or BFTM timing messages 126; and one or more propagation timing estimates 122 corresponding to the propagation times of BFTM or FTM timing messages 126 from the other mobile computing devices 100 (e.g., messages station B received from C, D, and E), or from the mobile computing device 100 sending the BFTM allocation message (e.g., BFTM allocation message 126 received by station B from station A). Examples of the BFTM allocation messages 126 are illustrated in FIG. 3A and described in more detail below. Examples of the BFTM timing messages 128 are illustrated in FIG. 3B and described in more detail below.

[0042] Propagation timing estimates 122 are time estimates that are determined based on the TODs and TOAs of the BFTM allocation messages 126 or the BFTM timing messages 128. The device location component 130 may determine the location of the mobile computing device 100 or other mobile computing devices 100 by applying a particular constant (e.g., the speed of light or approximately 299,792,458 m/s) to the propagation timing estimates 122 to determine, based on the TODs 118 and TOAs 120 how far away the mobile computing devices 100 are from each other. Some examples of this disclosure batch multiple TOAs associated with other mobile computing devices 100 into a single BFTM timing message 128 for a given responding mobile computing device 100, and these TOAs may be used to determine the locations of the other mobile computing devices 100 using the responding mobile computing devices 100's single BFTM timing message 128.

[0043] Additionally, the device location component 130 may be configured to identify responding mobile computing devices 100 within a given area or proximity to the mobile computing device 100. In some examples, proximity is determined based on receipt of signaling from the other mobile computing devices 100 in the area. Alternatively or additionally, the device location component 130 may use the propagation timing estimates 122 communicated in the BFTM timing messages 128 to calculate distances between the mobile computing devices 100. Using these calculated distances, the device location component 130 may build a relative or absolute mapping of the mobile computing devices 100 that are exchanging BFTM allocation or timing messages 126, 128. For example, if station B may determine that station D is 3m away based on the propagation timing estimate 122 calculated from the TOD of a BFTM timing message 128 from station B and the corresponding TOD that station B's BFTM timing message 128 was received at station D. This relative 3m distance may then be compared by station D (or any other station receiving or calculating the distance) with relative distances of other stations to determine the location of station B. Using the BFTM timing messages 128 discussed herein, mobile computing devices 100 can be accurately located within a spatial resolution of about 3cm, which is largely sufficient for most mobile-device applications.

[0044] To give a more concrete example, suppose station A transmits a BFTM allocation message 126 to stations B, C, D, and E in a given area. Station A's BFTM allocation message 126, in some examples, includes a TOD indicating the message's time of transmission from station A. Stations B, C, D, and E receive the BFTM allocation message 126, and each capture the TOA that the BFTM allocation message 126 was received. The BFTM allocation message may also include a scheduling order indicating particular timing periods the stations B, C, D, and E are to transmit BFTM timing messages 128, e.g., stations B, C, D, and E may be scheduled to transmit at times Tl, T2, T3, and T4 on a particular or varying RF channel. Each station may then transmit a BFTM timing message 128 during the respectively scheduled time that includes the TOA that the station received the BFTM allocation message 126, the TOD of the station's BFTM timing message 128, and/or a propagation timing estimate 122 indicating the distance of the station from the scheduling station A. Such a propagation timing estimate 122 may be computed by the station using the TOD from the BFTM allocation message 126, the TOA that the station received the BFTM allocation message 126, and one or more constants (e.g., the speed of light).

[0045] In some examples, the BFTM timing messages 128 are received by some or all of the responding stations (e.g., stations B-E) in addition to the scheduling station (e.g., station A). For example, responding station B may transmit a BFTM timing message 128 that is received by scheduling station A and also responding stations C, D, and E. In some examples, each station identifies the TOA that the BFTM timing message 128 was received by the station (e.g., the TOA that station D received the BFTM timing message of station B), and uses the TOD in the BFTM timing message 128 along with a propagation constant (e.g., the speed of light) to determine the propagation timing estimate 122 between the two stations. Continuing along with the aforesaid example, station D may receive the BFTM timing message 128 of station B; identify the TOA that the message was received at station D, and determine a propagation timing estimate 122 between stations B and D using the TOD in the BFTM timing message 126 and the identified TO A indicating when station D received the BFTM timing message 126.

[0046] In some examples, these additional timing and propagation timing estimate parameters— again, the TOD of the BFTM timing message 128 from station B, the TO A that station D received the BFTM timing message 128 from station B, and the propagation timing estimate calculated based on such timing parameters— are included in the BFTM timing messages 128 of the mobile computing devices 100. Thus, the BFTM timing message 128 of station D may include the TOD, TO A, and propagation timing estimate corresponding to the BFTM timing message 128 received from station B in addition to the TOA, TOD, and the propagation timing estimate of station D with respect to the BFTM allocation message 126 from station A. In this manner, the BFTM timing messages 128 are scalable to include timing and propagation information from other responding mobile stations as well as the scheduling mobile station. Piggybacking the timing and propagation information from other mobile stations within a single BFTM timing message 128 drastically reduces the number of messages needing to be communicated to determine the propagation times between the various mobile stations. These propagation times may be used in determining device locations, so the various examples disclosed herein also eliminate much of the signaling traffic needed to locate devices in a given area.

[0047] FIG. 2 illustrates a block diagram of mobile computing devices 100 communicating BFTM allocation messages 126 and BFTM timing messages 128 in accordance with some examples disclosed herein. The depicted example shows five mobile computing devices 100A-E within a given area (e.g., inside a building, in a marketplace, passing along a street, etc.) and that wirelessly communicate with each other, either over a network 132 or point-to-point. Of course, the disclosed techniques may include more or fewer than five mobile computing devices 100. For purposes of the disclosure, and to aid the reader, the mobile computing device 100 A that transmits the BFTM allocation message 126 is referenced as the "scheduling mobile computing device," and the mobile computing devices 100B-E that respond to the BFTM allocation message are referenced as the "responding mobile computing devices." In one example, the scheduling mobile computing device 100 A is a group owner from a peer-to-peer group that acts as an initiator for transmitting the BFTM allocation message 126 that coordinates the order of responding mobile computing devices 100B-E transmitting the BFTM timing messages 128. [0048] In some examples, location detection service are provided among the mobile computing devices 100A-E by the scheduling mobile computing device 100 A initially and wirelessly broadcasting a BFTM allocation message 126 within a given broadcast area or radius, as shown by the dotted lines. Responding mobile computing devices 100B-E receive the BFTM allocation message 126, assign a TOA at the time of receipt of the BFTM allocation message 126, generate a BFTM timing message 128 to respond back with, and transmit the generated BFTM timing message 128 during the scheduled contention-free time period according to the scheduling instructions in the BFTM allocation message 126. For example, responding mobile computing device 100B may be designated to transmit its BFTM timing message 128 at time T2, responding mobile computing device lOOC may be designated to transmit its BFTM timing message 128 at time T3, responding mobile computing device 100D may be designated to transmit its BFTM timing message 128 at time T4, and responding mobile computing device 100E may be designated to transmit its BFTM timing message 128 at time T5.

[0049] The illustrated example depicts only one scheduling mobile computing device 100 A broadcasting a BFTM allocation message 126 and the responding mobile computing devices 100B-E responding back with BFTM timing messages 126. In some examples, each, or a subset, of the mobile computing devices 100A-E act as the scheduling mobile computing device 100 at different times, causing the other mobile computing devices 100 to responsively operate as responding mobile computing devices 100. For example, after the depicted transmission of BFTM timing messages 128 from mobile computing devices 100B-E in response to the BFTM allocation message 126 from mobile computing device 100 A, mobile computing device 100B may act as the scheduling mobile computing device 100 by sending a BFTM allocation message 126 that causes mobile computing devices 100 A and C-E to respond with BFTM timing messages 128. Similarly, mobile computing devices lOOC-E may also operate— either in sequence (in some examples)— as the scheduling mobile computing device 100B, causing the rest of the mobile computing devices 100A-E to respond with BFTM timing messages 128.

[0050] Focusing on the depicted example, the BFTM allocation message 126 includes a scheduling order that dictates timing periods for responding mobile computing devices A-E to transmit their respective BFTM timing messages 128. Mobile computing device 100A is included in the scheduling order, in some examples, because mobile computing device 100 A may operate as both a scheduling mobile computing device 100 when sending the BFTM allocation message 126 and a responding mobile computing device 100 when sending a BFTM timing message 128. As previously discussed, the BFTM timing messages 128 may include a TOD, a TOA, and/or a propagation timing estimate associated with the responding mobile computing device 100's receipt of and response to the BFTM allocation message 126. Additionally or alternatively, the BFTM timing messages 128 may include identifiers of other mobile computing devices 100 (e.g., devices A and C-E) from which the responding mobile computing device 100 (e.g., device B) has previously received BFTM or FTM messages as well as corresponding TOAs, TODs, and/or propagation timing estimates of those previously received BFTM or FTM messages.

[0051] Such additional timing and propagation information from other mobile computing devices 100 may, in some examples, be included within a single BFTM timing message 128, reducing the need to transmit multiple messages from those other devices in order to convey such information and also extending the reach of information gathered at each mobile computing device 100. For example, a BFTM timing message 128 received by mobile computing device 100 A from mobile computing device 100B that includes TOA, TOD, and propagation timing estimates for BFTM transmissions between mobile computing devices 100B and 100D provides mobile computing device 100 A with information it would conventionally not be getting— i.e., timing and propagation information between devices B and D.

[0052] Moreover, the BFTM timing message 128 may also include TOA, TOD, and/or propagation timing estimates of another responding mobile computing device 100B- E's receipt of the BFTM allocation message 126 from the scheduling mobile computing device 100 A. So, in some examples, device C communicates the propagation and timing information of device E's receipt of the BFTM allocation message 126 from device A, and this propagation and timing information is added to the BFTM timing message 128 from device C. Some examples may alternatively not communicate timing and/or propagation information of another mobile computing device 100's receipt of the BFTM allocation message 126, while still communicating exchanged BFTM timing messages 128 or FTM messages.

[0053] FIG. 3A illustrates one example of a BFTM allocation message 126. The BFTM allocation message 126 includes several frames 302-350B that individually include various octets of information. Octet quantities are provided above each frame. The illustrated BFTM allocation message 126 of FIG. 3 is but one example. Other examples may represent information in other binary, hexadecimal, or other formats; use different sets of octets; include different frames 302-350B than those illustrated; or rearrange the frames 302-350B in alternative sequences. To further illustrate the given example, the individual frames are discussed below. Not all of the shown frames 302-350B are included in all examples.

[0054] Frame control 302 indicates the type of frame being transmitted, which may include a designation for an acknowledgment (ACK) frame, a BFTM allocation frame 126, a BFTM timing frame 128, or some other type of frame. Duration 304 indicates the time or period of the BFTM allocation message 126. Receiver address 306 indicates a unique address (e.g., media access control or "MAC" address) of the destination mobile computing device 100 to receive the BFTM allocation frame 126, and transmitter address 308 indicates the scheduling mobile computing device 100 transmitting the BFTM allocation message 126. BSSID 310 identifies the network or a wireless access point (WAP) of the scheduling mobile computing device 100. Sequence control 312 indicates the sequence number of the BFTM allocation message 126. HT control field 314 indicates the type of message of the BFTM allocation message 126 (e.g., a management message indication). FCS 318 is a checksum value.

[0055] For the BFTM allocation message 126, action field 316 provides additional information relevant to the BFTM timing message 128, TODs, TO As, and the like. Action field 316 includes the following field: category 320, BFTM action 322, BFTM dialog token 324, TOD 326, maximum TOD error 328, number of BFTM slots 330, BFTM slot duration 332, and the BFTM peer MAC addresses 334A of the responding mobile computing devices being scheduled. Category 320 and BFTM action 322 are implementation fields that designate the message as being a BFTM allocation message 126.

[0056] To allow multiple parallel BFTM operations from different subsets of mobile computing devices 100 to occur, BFTM dialog token used to uniquely identify a BFTM timing realization. Different BFTM dialog tokens 324 may be indicate different BFTM transactions. For example, one BFTM dialog token 324 may indicate BFTM operations occurring when the mobile computing device 100A is the scheduling mobile computing device 100. In some examples, multiple BFTM operations are occurring at the same time, so the BFTM dialog token 324 provides a way to distinguish between the BFTM operations. In some examples, BFTM timing messages 128 responding to one particular BFTM allocation message 126 with a given TOD 118 responds with different TOA values than BFTM timing messages responding to a completely different BFTM allocation message 126. Thus, using the BFTM dialog token 324 allows the mobile computing devices 100 to respond to any other mobile computing device 100 initiating BFTM operations. [0057] For the BFTM allocation message 126, TOD 326 is the time of delivery of the BFTM allocation message 126 captured from the clock 106. Maximum TOD error 328 provides an estimation of the maximum TOD effort allotted to specific chipsets of the scheduling mobile computing device 100. Maximum TOD error 328 may be set by the manufacturer of chipsets at the PHY layer. In some examples, TOD 326 and Maximum TOD error 328 define the TOD and the maximum tolerable TOD measurement in multiples

[0058] The number of BFTM slots 330 indicates the number of transmission slots scheduled for the mobile computing devices 100. Following the example shown in FIG. 2, a multiple (e.g., 1, 2, 3) of five slots may be indicated to account for the mobile computing devices 100A-E. For example, ten slots may be specified allowing each mobile computing device 100A-E to transmit a BFTM timing message 128. BFTM slot duration 332 indicates the time duration of the exclusive channel reservation for each BFTM transmission. Finally, a varying number of instances of BFTM peer MAC addresses 334A-N are provided to represent the MAC addresses of each mobile computing device 100 allocated by the BFTM allocation message 126 to transmit the BFTM timing messages 128. For example, mobile computing device 100B may be scheduled to transmit at time T2, mobile computing device lOOC may be scheduled to transmit at time T3, mobile computing device 100E may be scheduled to transmit at time T4, mobile computing device 100 A may be scheduled to transmit at time T5, mobile computing device 100B may be scheduled to transmit at time T6, mobile computing device lOOC may be scheduled to transmit at time T7, and mobile computing device 100E may be scheduled to transmit at time T8, and mobile computing device 100A may be scheduled to transmit at time T9. In some examples, the scheduled order is repeated or reversed after the final time T9.

[0059] As for the channel access mechanism utilized for acquiring channel access rights for transmitting the BFTM allocation frame 126, three exemplary (but non-limiting) examples are disclosed herein. In the first example, the scheduling mobile computing device 100 contends regularly for gaining channel access via carrier sense multiple access with collision avoidance (CSMA/CA) techniques, as used in a distributed coordination function (DCF) mode. In a second example, a Request-To-Transmit/Clear-To-Transmit (RTS/CTS) frame exchange is performed between the scheduling and one or more responding mobile computing devices prior to the transmission of the BFTM allocation frame 126. This may be done to increase the odds that there will be no collisions for the transmission of the BFTM allocation message 126 by setting the network allocation vector (NAV) on the mobile computing device 100 to receive the RTS/CTS frames for the exact or nearly exact duration of the BFTM allocation message 126. In a third example, an a-priori negotiation initiated by the scheduling mobile computing device 100 is conducted among a subset of responding mobile computing devices 100 of interest as to define repeating fixed-duration time intervals during which all the mobile computing devices 100 involved (scheduling and responding) are scheduled to avoid accessing the channel (e.g., setting NAVs) and will wait for the transmission of the BFTM allocation message 126.

[0060] In alternative examples of the BFTM allocation message 126 aimed at reducing even further the signaling overhead, the BFTM peer MAC address field 334 is replaced by a "BFTM Peer Node ID" frame that indicates a node identifier for the mobile computing device 100 allocated for transmitting a BFTM timing message 128. The algorithm for node ID allocation of each mobile computing device 100 may vary in different instances and is beyond the scope of this disclosure.

[0061] One positive aspect about the reception of the BFTM allocation message 126 by any other mobile computing device 100 is that the Duration frame 304 in the BFTM allocation message 126 sets the NAV of responder mobile computing devices 100 for the duration of all subsequent BFTM slots 330 allocated, thus effectively creating a contention- free period. This allows each subsequent BFTM frame sent during the BFTM slots to not contend for accessing a transmission channel. In other words, the BFTM frames can be transmitted in a contention-free manner. As such, the BFTM measurement allocations determined by the BFTM allocation message 126 allow diminished signaling overhead and increased efficiency in dense deployment situations.

[0062] The illustrated frames of FIG. 3A are provided merely for explanatory purposes to illustrate two different example implementations. All implementations are not limited to the depicted frames. Alternative examples include additional and alternative frames without departing from the scope of this disclosure.

[0063] FIG. 3B illustrates one example of a BFTM timing message 128. The illustrated BFTM timing message 128 includes many of the same fields as the BFTM allocation message 126 shown in FIG. 3 A, only from the perspective of a responding mobile computing device 100. Specifically, the depicted BFTM timing message 128 includes the following fields of information: frame control 302, duration 304, receiver address 306, transmitter address 308, BSSID 310, sequence control 312, HT control 314, action field 316, and FCS 318. Like the BFTM allocation message 126 discussed above relative to FIG. 3A, the BFTM timing message 128 includes the following fields of information in the action field 316: category 320, BFTM action 322, BFTM dialog token 324, TOD 326 (i.e., times of the BFTM timing message 128 instead of the BFTM allocation message 126), and maximum TOD error 328. The BFTM timing message 128 also includes: a number of BFTM reports 430; a maximum TOA error threshold 432; multiple BFTM reports 440A-N; a number of PTE reports 442; a maximum PTE error 444; and multiple PTE reports 446 A- N.

[0064] Frame control 302 indicates the type of frame being transmitted, which may include a designation for an acknowledgment (ACK) frame, a BFTM timing frame 126, or some other type of frame. Duration 304 indicates the time or period of the BFTM timing message 128. Receiver address 306 indicates a unique address (e.g., MAC address) of the destination mobile computing device 100 to receive the BFTM allocation frame 126, and transmitter address 308 indicates the responding mobile computing device 100 transmitting the BFTM timing message 128. BSSID 310 identifies the network or a wireless access point (WAP) of the responding mobile computing device 100. Sequence control 312 indicates the sequence number of the BFTM timing message 128. HT control field 314 indicates the type of message of the BFTM timing message 128 (e.g., a management message indication). FCS 318 is a checksum value.

[0065] Looking at the action field 316 of the BFTM timing message 128, category 320 and BFTM action 322 are implementation fields that designate the message as being a BFTM timing message 128. BFTM dialog token 324 is used to uniquely identify the BFTM timing message 128, providing a way to distinguish the BFTM timing message 128 from other BFTM or FTM messages. In some examples, multiple BFTM operations are occurring at the same time, so the BFTM dialog token 324 provides a way to distinguish between the BFTM operations. BFTM timing messages 128 responding to one particular BFTM allocation message 126 with a given TOD 118 may respond with different timing and propagation values than BFTM timing messages 128 responding to a completely different BFTM allocation message 126.

[0066] For the BFTM timing message 128, TOD 326 is the time of delivery of the BFTM timing message 126 captured from the clock 106. Maximum TOD error 328 provides an estimation of the maximum TOD error allotted to specific chipsets of the responding mobile computing device 100. Maximum TOD error 328 may be set by the manufacturer of chipsets at the PHY layer. In some examples, TOD 326 and Maximum TOD error 328 define the TOD and the maximum tolerable TOD measurement in multiples of 0.1 μβ. [0067] The number of BFTM reports 430 and the number of PTE reports 442 respectively indicate a number of additional BFTM (or FTM) timing messages 126 and propagation timing estimates previously received by the responding mobile computing device 100 from other mobile computing devices 100. As previously discussed, the BFTM timing message 126 may include timing and propagation information from other responding or scheduling mobile computing devices 100. For example, station B may receive timing and propagation data of BFTM timing messages from stations C, D, and E. Such timing and propagation data is included in the BFTM report 440A-N and PTE report 446A-N frames, respectively, which are discussed in more detail below. The number of BFTM reports 430 and the number of PTE reports 442 indicate how many of these timing and propagation reports are included in the BFTM timing message 128.

[0068] Maximum TOD error 432 indicates the maximum tolerable TOD measurement error to be used for the TOD fields reported by this BFTM timing message 128. Such error may be chipset dependent or user-specified.

[0069] The BFTM reports 440A-N are provided to indicate the TOAs 120 of

BFTM or FTM messages previously sent to or by other responding mobile computing devices 100. More specifically, the TOAs 444A-N may indicate the TOA of a previously sent FTM or BFTM message to another mobile computing device 100, either from the mobile computing device 100 sending the BFTM timing message 128 or another mobile computing device 100. For example, if station B is sending the BFTM timing message 128, the BFTM peer MAC address 442A may indicate station C and the corresponding TOA 444A may indicate the TOA at which station C received a message from either station B or stations A, D, or E. In an alternative example, if station B is sending the BFTM timing message 128, the BFTM peer MAC address 442 A may indicate station C and the corresponding TOA 444A may indicate the TOA at which station B received a message from station C. So the BFTM reports 440 may indicate the TOAs 444 that a responding mobile computing device 100 sending the BFTM timing message 128 recorded when receiving BFTM or FTM messages from other mobile computing devices 100, the TOAs 444 of other mobile computing devices 100 receiving BFTM or FTM messages from the responding mobile computing device 100 sending the BFTM timing message 128, TOAs 444 of other mobile computing devices 100 receiving BFTM or FTM messages from still other mobile computing devices 100, or a combination thereof.

[0070] The BFTM timing frame 128 may also indicate a number of PTE reports 442, indicate a maximum PTE error 444, and include multiple PTE reports 446A-N, or some combination thereof. The number of PTE reports 442 determines the number of PTE reports 446 that are included in the BFTM timing message 128. The Maximum PTE report error 444 may indicate the maximum error (e.g., in multiples of Ο. ΐμβ) for the PTEs in this BFTM timing message 128.

[0071] The PTE reports 446A-N may include identifiers of mobile computing devices 100 (PTE peer MAC addresses 460 A-N) and corresponding PTEs 462 A-N indicating the propagation times of previously sent BFTM or FTM messages relative to the identified responding mobile computing device 100 or other mobile computing devices 100. For example, stations C, D, and E may be identified by MAC address (or other identifier, such as an Internet Protocol address, or the like) in a BFTM timing message 128 of station B, corresponding PTEs 462 may be provided that indicate the respective propagation delays of stations C, D, and E with respect to station B or each other (e.g., between C and D, D and E, etc.). In some examples, PTEs 462A-N represent previously calculated PTEs between two mobile computing devices 100 based on TODs and TO As of BFTM or FTM messages communicated between the two. By batching PTEs 462A-N in the BFTM timing messages 128, the number of messages needing to be exchanged to form a mapping of the locations of proximate mobile computing devices 100 can be reduced dramatically.

[0072] The illustrated frames of FIG. 3A are provided merely for explanatory purposes to illustrate two different example implementations. All implementations are not limited to the depicted frames. Alternative examples include additional and alternative frames without departing from the scope of this disclosure.

[0073] FIG. 4A is a timing diagram showing various mobile computing devices 100A-E communicating different BFTM messages 402-410 at times T1-T5. A scheduling mobile computing device 100 A broadcasts a BFTM allocation message 126 (402) at time Tl that schedules a set of responding mobile computing devices 100B-E to transmit BFTM timing messages 128 or FTM messages (402-410) at times T2-T5.

[0074] In some examples, the illustrated pattern of transmissions 402-410 and corresponding times T1-T5 are scheduled in BFTM allocation message 126 (402) using the following messages fields: BFTM slots 328, BFTM slot duration 332, and the BFTM peer MAC addresses 334A-N. In particular, BFTM slots 328 specify the number of slots open for responding mobile computing devices 100A-E to individually transmit. BFTM slot duration 332 designates the amount of time for each to transmit, which may be a specific unit of time (e.g., Ins) or some multiple of time (e.g., two multiples of 0.1 μβ). In some examples, the amount of time is uniform between all responding mobile computing devices 100B-E. In still other examples, the time varies (e.g., T2-T3 is different than T4-T5).

[0075] During their respectively scheduled BFTM transmission times, responding mobile computing devices 100A-E— device 100 A may operate as both a scheduling and responding device 100— transmit a BFTM timing message 128 or FTM message that can be captured by the rest of the mobile computing devices 100A-E (in some examples) or just the scheduling mobile computing device 100A (in other examples). In some examples, the BFTM allocation message 126 includes an identifier for the response BFTM or FTM messages in order to associate the response messages to the BFTM allocation message 126.

[0076] Responsive BFTM timing messages 126 may include a TO A indicating when the responding mobile computing devices 100B-E received the BFTM allocation message 126 and a TOD for when the responsive BFTM timing message 128 was sent. Additionally, the BFTM timing message 128 may also include one or more TOAs and/or PTEs of other responding mobile computing devices 100 associated with previous communications with the responding mobile computing device 100 or between the other mobile computing devices 100 themselves. Specifically, these PTEs may indicate the propagation time required to communicate the BFTM allocation message 126 between the scheduling and responding mobile computing devices 100 (e.g., station A to stations B, C, D, or E), or communicate BFTM timing messages 128 (or FTM messages) between the responding computing devices 100 (e.g., stations B-E to stations E-B).

[0077] FIG. 4B illustrates various times associated with the BFTM messages 402- 418 communicated between mobile computing devices 100A-E. The depicted messages illustrate the messages between two different mobile computing devices 100A-E that are received (tRX messages) and transmitted (tTX messages). The messages themselves indicate the two mobile computing devices 100A-E involved in the message transaction, with the transmitting device listed first and the receiving device listed second. As shown, mobile computing device 100A transmits BFTM allocation message 402 at time Tl (i.e., tTX[A,*]) at which time it has received no other messages (i.e., tRX:0). The BFTM allocation message 402 is received at responding mobile computing devices 100B-E, as shown by tRX[A,B] at device 100B; tRX[A,C] at device lOOC; tRX[A,D] at device 100D; and tRX[A,E] at device 100E respectively at times T2, T3, T4, and T5, respectively.

[0078] In some examples, the mobile computing devices 100A-E transmit BFTM timing messages 404-418 at times T2-T5. The rest of the mobile computing devices 100 A- E receive the BFTM timing messages 404-410 of the other mobile computing devices 100A- E and may include the timing an propagation information of from those messages in the mobile computing devices 100A-E's BFTM timing message. Specifically, the BFTM timing message 404 transmitted by mobile computing devices 100B includes the TOD, TO A, and/or PTE associated with the BFTM allocation message 402 received at the mobile computing device 100B. The BFTM timing message 406 transmitted by mobile computing device lOOC includes the TODs, TOAs, and/or PTEs associated with the BFTM allocation message 402 from device 100 A and the BFTM timing message 404 from device 100B received at the mobile computing device lOOC. The BFTM timing message 408 transmitted by the mobile computing device 100D includes the TODs, TOAs, and/or PTEs associated with the BFTM allocation message 402 from device 100 A and the BFTM timing messages 404 and 406 from devices B and C, respectively, received at the mobile computing device 100D. The BFTM timing message 410 transmitted by the mobile computing device 100E includes the TODs, TOAs, and/or PTEs associated with the BFTM allocation message 402 from device 100A and the BFTM timing messages 404, 406, and 408 from devices B, C, and D, respectively, received at the mobile computing device 100D.

[0079] FIG. 5 is a flow chart diagram illustrating a work flow 500 for generating a BFTM allocation message 126. According to work flow 500, a scheduling mobile computing device 100 identifies responding mobile computing devices in a particular area, such as an indoor building, as shown at block 502. The scheduling mobile computing device 100 generates a BFTM allocation message 126 in the following manner. A contention-free period for timing measurement messages (BFTM or FTM) is determined by the scheduling mobile computing device 100, as shown at block 504. A scheduling order for the responding mobile computing devices 100 to transmit the timing measurement messages is determined by the scheduling mobile computing device 100, as shown at block 506. In some examples, a TOD for the BFTM allocation message is determined from a clock of the scheduling mobile computing device 100 just prior (e.g., within milliseconds, nanoseconds, etc.) to transmission of the BFTM allocation message 126 to avoid extra delays incurred by processing, as shown at block 508. The BFTM allocation message with frames indicating the TOD, scheduling order, and the contention-free period is then generated and transmitted to the responding computing devices 100, as shown at blocks 510 and 512, respectively.

[0080] FIG. 6 is a flow chart diagram illustrating a work flow 600 for generating a BFTM allocation message 126. According to work flow 600, mobile computing devices are identified in a particular area by a scheduling mobile computing device 100, as shown at block 602. The scheduling mobile computing device 100 generates a BFTM allocation message 126 in the following manner. The scheduling mobile computing device 100 gains access via CSMA/CA to obtain a contention-free period for the other mobile computing devices to transmit timing measurement messages (BFTM or FTM), as shown at block 604. A scheduling order for the responding mobile computing devices 100 to transmit the timing measurement messages is assigned by the scheduling mobile computing device 100, as shown at block 606. A TOD for the BFTM allocation message is determined from a clock of the scheduling mobile computing device 100 just prior to transmission of the BFTM allocation message 126, as shown at block 608. The BFTM allocation message with frames indicating the TOD, the contention-free period, and the scheduling order is generated and transmitted to the responding computing devices 100, as shown at blocks 610 and 612, respectively.

[0081] FIG. 7 is a flow chart diagram illustrating a work flow 700 for generating a BFTM timing message 128. A responding mobile computing device 100 receives a BFTM allocation message 126 from a scheduling mobile computing device 100, as shown at block 702. From the BFTM allocation message 126, the responding mobile computing device 100 accesses a scheduling order. The responding mobile computing device 100 determines a TO A of the BFTM allocation message 126 and a scheduled future time to transmit a BFTM timing message 128, as shown at block 704.

[0082] The responding mobile computing device 100 determines whether any TOAs or PTEs in other previously received BFTM or FTM messages need to be included in the BFTM timing message 128, as shown at decision blocks 706 and 708, respectively. If so, the TOAs and PTEs are retrieved from storage on the responding mobile computing device 100. as shown at blocks 710 and 712, respectively, and included in the BFTM timing message generated by the responding mobile computing device 100, as shown at block 714. Corresponding device identifiers (e.g., MAC, IP, or the like) may also be included to indicate devices associated with the retrieved TOAs and PTEs. Additionally or alternatively, a TOD for the BFTM timing message 128 is also determined. Though not shown for clarity, TODs of the previous BFTM timing messages 128 that provided the additional TOAs and PTEs being added to the current BFTM timing message 128 may also be included. Once generated, the BFTM timing message 128 is transmitted at the scheduled time to the other mobile computing devices 100 in the area, as indicated at block 716.

[0083] In some examples, the operations illustrated in FIGS. 5-7 may be implemented as software instructions encoded on computer- storage media (e.g., memory), in hardware programmed or designed to perform the operations, or both. For example, aspects of the disclosure may be implemented as an SoC or other circuitry including a plurality of interconnected, electrically conductive elements.

Additional Examples

[0084] Some examples are directed to a first mobile computing device that includes a clock, a memory area storing machine-executable instructions for generating a BFTM timing message, and a processor. In some examples, the processor is configured to: receive a BFTM allocation message from a scheduling mobile computing device, determine a scheduled time to transmit the BFTM timing message based on the BFTM allocation message, receive one or more other BFTM timing messages from one or more responding mobile computing devices, determine one or more TO As associated with the one or more other BFTM timing messages, generate the BFTM timing message comprising the one or more TOAs of the one or more other BFTM timing messages, and transmit the BFTM timing message.

[0085] Some examples are directed to execution of various steps for generating and transmitting BFTM timing messages for use in location-detection services. The steps include: receiving a BFTM allocation message from a scheduling mobile computing device, determining a scheduled time to transmit a BFTM timing message based on the BFTM allocation message, receiving one or more other BFTM timing messages from one or more responding mobile computing devices, determining one or more TOAs associated with the one or more other BFTM timing messages, generating the BFTM timing message comprising the one or more TOAs of the one or more other BFTM timing messages, and transmitting the BFTM timing message.

[0086] Some examples are directed to computer-storage memory embodied with machine-executable instructions for generating and transmitting BFTM timing messages for use in location-detection services. The instructions, when executed, perform the following functions: receiving a BFTM allocation message from a scheduling mobile computing device, determining a scheduled time to transmit a BFTM timing message based on the BFTM allocation message, receiving one or more other BFTM timing messages from one or more responding mobile computing devices, determining one or more propagation timing estimates associated with the one or more other BFTM timing messages; generating the BFTM timing message comprising the one or more propagation timing estimates of the one or more other BFTM timing messages, and transmitting the BFTM timing message.

[0087] Alternatively or in addition to the other examples described herein, examples include any combination of the following: [0088] a processor configured to include a first BFTM dialog token in the BFTM timing message, the BFTM dialog token indicating a BFTM sequence;

[0089] a transceiver receiving a second BFTM allocation message from a second mobile computing device, the second BFTM allocation message comprising a second BFTM dialog token that is different from the first BFTM dialog token and indicates a first set of BFTM transactions differing from a second set of BFTM transactions associated with the BFTM allocation message;

[0090] inclusion of propagation timing estimates associated with the one or more other BFTM timing messages from the one or more responding computing devices in the BFTM timing messages;

[0091] a processor is further configured to include in the BFTM timing message a time of delivery (TOD) for the BFTM timing message;

[0092] a processor configured to include in the BFTM timing message a maximum TOD error indicating a maximum tolerable TOD measurement error; or

[0093] one or more device identifiers of the one or more responding mobile computing devices in the BFTM timing message.

[0094] While the aspects of the disclosure have been described in terms of various examples with their associated operations, a person skilled in the art would appreciate that a combination of operations from any number of different examples is also within scope of the aspects of the disclosure.

Exemplary Operating Environment

[0095] Although described in connection with an exemplary computing device, examples of the disclosure are capable of implementation with numerous other general- purpose or special-purpose computing system environments, configurations, or devices. Examples of well-known computing systems, environments, and/or configurations that may be suitable for use with aspects of the disclosure include, but are not limited to, smart phones, mobile tablets, mobile computing devices, personal computers, server computers, hand-held or laptop devices, multiprocessor systems, gaming consoles, microprocessor- based systems, set top boxes, programmable consumer electronics, mobile telephones, mobile computing and/or communication devices in wearable or accessory form factors (e.g., watches, glasses, headsets, or earphones), network PCs, minicomputers, mainframe computers, distributed computing environments that include any of the above systems or devices, and the like. Such systems or devices may accept input from the user in any way, including from input devices such as a keyboard or pointing device, via gesture input, proximity input (such as by hovering), and/or via voice input.

[0096] Examples of the disclosure may be described in the general context of computer-executable instructions, such as program modules, executed by one or more computers or other devices in software, firmware, hardware, or a combination thereof. The computer-executable instructions may be organized into one or more computer-executable components or modules. Generally, program modules include, but are not limited to, routines, programs, objects, components, and data structures that perform particular tasks or implement particular abstract data types. Aspects of the disclosure may be implemented with any number and organization of such components or modules. For example, aspects of the disclosure are not limited to the specific computer-executable instructions or the specific components or modules illustrated in the figures and described herein. Other examples of the disclosure may include different computer-executable instructions or components having more or less functionality than illustrated and described herein. In examples involving a general-purpose computer, aspects of the disclosure transform the general- purpose computer into a special-purpose computing device when configured to execute the instructions described herein.

[0097] Exemplary computer readable media include flash memory drives, digital versatile discs (DVDs), compact discs (CDs), floppy disks, and tape cassettes. By way of example and not limitation, computer readable media comprise computer storage media and communication media. Computer storage media include volatile and nonvolatile, removable and non-removable media implemented in any method or technology for storage of information such as computer readable instructions, data structures, program modules or other data. Computer storage media are tangible and mutually exclusive to communication media. Computer storage media are implemented in hardware and exclude carrier waves and propagated signals. Computer storage media for purposes of this disclosure are not signals per se. Exemplary computer storage media include hard disks, flash drives, and other solid-state memory. In contrast, communication media typically embody computer readable instructions, data structures, program modules, or other data in a modulated data signal such as a carrier wave or other transport mechanism and include any information delivery media.

[0098] The examples illustrated and described herein, as well as examples not specifically described herein but within the scope of aspects of the disclosure, constitute exemplary means for generating and transmitting a BFTM timing message from a mobile device to other mobile computing devices in a given area. For example, the elements described in FIG. 1, such as when encoded to perform the operations illustrated in FIG. 7, constitute exemplary means for a responding mobile computing device to receive a BFTM allocation message 126, exemplary means for determining a schedules time for transmitting a BFTM timing message, exemplary means for retrieving TOAs and PTEs associated with previously received BFTM or FTM messages, exemplary means for generating the BFTM timing message to include the retrieved TOAs and PTEs, and exemplary means for transmitting the so-generated BFTM timing message 126.

[0099] The order of execution or performance of the operations in examples of the disclosure illustrated and described herein is not essential, and may be performed in different sequential manners in various examples. For example, it is contemplated that executing or performing a particular operation before, contemporaneously with, or after another operation is within the scope of aspects of the disclosure.

[00100] When introducing elements of aspects of the disclosure or the examples thereof, the articles "a," "an," "the," and "said" are intended to mean that there are one or more of the elements. The terms "comprising," "including," and "having" are intended to be inclusive and mean that there may be additional elements other than the listed elements. The term "exemplary" is intended to mean "an example of." The phrase "one or more of the following: A, B, and C" means "at least one of A and/or at least one of B and/or at least one of C."

[00101] Having described aspects of the disclosure in detail, it will be apparent that modifications and variations are possible without departing from the scope of aspects of the disclosure as defined in the appended claims. As various changes could be made in the above constructions, products, and methods without departing from the scope of aspects of the disclosure, it is intended that all matter contained in the above description and shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense.