Location-determining system for radio clients within local-area spaces

Systems, devices, features, and/or methods for determining a location of a mobile device are disclosed. A method may include (a) receiving, into a mobile device, a common RF signal on a common carrier frequency, wherein the common RF signal includes a respective RF signal output by each of three or more transmitters on a common time basis in a round-robin manner, and wherein each of the three or more transmitters is positioned at a known location, (b) capturing data representing the common RF signal, (c) based on the captured data, discriminating between each respective RF signal that forms the received common RF signal, (d) determining a relative phase shift of each respective RF signal, and (e) determining the location of the mobile device based on the determined relative phase shifts and the known locations of the three or more transmitters.

BACKGROUND OF THE INVENTION

One emerging area of wireless communications is the provision of services based on a location of a mobile device. These location-based services may take various forms. For example, a location-based service may provide a user of the mobile device with a weather or traffic report relevant to the user's location. As another example, a location-based service may provide the user with a list of services or establishments (e.g., restaurants, parks, theatres, etc.) in the user's vicinity. As still another example, a location-based service may provide the user with an advertisement or coupon relevant to a product in the user's vicinity.

To facilitate the provision of location-based services to a user of a mobile device, a location-based service provider accurately determines and/or tracks the location of the mobile device. Various technologies currently exist to determine and/or track the location of a mobile device, the most prevalent of which are Global Positioning System (GPS) technologies and cellular network technologies. However, these technologies have drawbacks regarding accurate determination and/or tracking of a mobile device location, such as in an indoor environment. Accordingly, an improved location-determination system that is capable of accurately determining and/or tracking the location of a mobile device, such as, for example, in an indoor environment, is desirable.

SUMMARY OF THE INVENTION

According to one aspect, a method of determining a location of a mobile device is provided. For example, the method may include (a) receiving, into a mobile device, a common RF signal on a common carrier frequency, wherein the common RF signal includes a respective RF signal output by each of three or more transmitters on a common time basis in a round-robin manner, and wherein each of the three or more transmitters is positioned at a known location, (b) capturing data representing the common RF signal, (c) based on the captured data, discriminating between each respective RF signal that forms the received common RF signal, (d) determining a relative phase shift of each respective RF signal, and (e) determining the location of the mobile device based on the determined relative phase shifts and the known locations of the three or more transmitters.

DETAILED DESCRIPTION OF THE PRESENTLY PREFERRED EMBODIMENTS

FIG. 1is a simplified block diagram of exemplary communication system10configured to determine a location of a mobile device within an indoor environment22. As shown, communication system10may include a common signal source (CSS)12coupled to transmitters14A-14Dvia links16A-16D, a mobile device18, and a central server20. Other configurations may be provided as well.

It should be understood that the arrangements described herein are set forth for purposes of example only. As such, those skilled in the art will appreciate that other arrangements and other elements (e.g., components, interfaces, functions, orders of functions, etc.) can be used instead, some elements may be added, and/or some elements may be omitted altogether. Further, those skilled in the art will appreciate that many of the elements described herein are functional elements that may be implemented as discrete or distributed components or in conjunction with other components, and in any suitable combination and location. Still further, various functions described herein as being performed by one or more entities may be carried out by hardware, firmware and/or software. For instance, various functions may be carried out by a processor executing a set of program instructions written in any suitable programming language (e.g., C, C++, Java, etc.) and stored in memory.

CSS12may be any device configured to drive each of transmitters14A-14Dto output a respective radio frequency (RF) signal on a common time basis (i.e., CSS12may drive each of transmitters14A-14Dsuch that act as slave clocks that are coordinated with a master clock, and thus output respective RF signals that are synchronized according to the master clock). CSS12may include various components that enable it to perform this function. For instance, CSS12may include a high-precision master clock (e.g., a 300 MHz clock), one or more signal generators (e.g., a square wave generator, a sinusoidal wave generator, etc.), and one or more line drivers (e.g., differential line drivers). Additionally, in some embodiments, CSS12may include delay circuitry. Other configurations of CSS12are possible as well.

Each of transmitters14A-14Dmay be any device configured to be driven by CSS12to output a respective RF signal on a common time basis. Each of transmitters14A-14Dmay include various components that enable the transmitter to perform this function. For instance, each of transmitters14A-14Dmay include a line receiver (e.g., a differential line receiver), an amplifier, and an antenna. Additionally, in some embodiments, each of transmitters14A-14Dmay include a modulator. Other configurations of transmitters14A-14Dare possible as well.

In the embodiments described herein, transmitters14A-14Dare positioned at fixed locations within indoor environment22. For example, transmitters14A-14Dmay be affixed to or embedded in walls, ceilings, and/or floors within the indoor environment22. Other examples are possible as well. Each of transmitters14A-14Dmay thus have a known location within indoor environment22(e.g., a local coordinate). Further, in some embodiments, each of transmitters14A-14Dmay have a known location within a global environment (e.g., a geographic coordinate) as well.

Each of links16A-16Dmay be any wired and/or wireless link configured to carry one or more signals from CSS12to one of transmitters14A-14D. For instance, each of links16A-16Dmay include a first cable (e.g., a twisted-pair copper cable) configured to carry a first signal from CSS12to one of transmitters14A-14D. Additionally, in some embodiments, each of links16A-16Dmay include a second cable (e.g., a twisted-pair copper cable) configured to carry a second signal from CSS12to one of transmitters14A-14D. Each of links16A-16Dmay take other forms as well.

In the embodiments described herein, each of links16A-16Dwill have defined transmission properties, such as length and propagation speed. For instance, links16A-16Dmay all have the same defined transmission properties. Alternatively, links16A-16Dmay have different defined transmission properties. In either case, CSS12may use the defined transmission properties of links16A-16Dto ensure that all transmitters14A-14Dare being driven on a common time basis.

Mobile device18may be any device configured to receive and process RF signals from transmitters14A-14Dand send wireless communications to central server20. The mobile device18is a personal navigation device (“PND”), a portable navigation device, a cellular telephone, a mobile phone, a personal digital assistant (“PDA”), a watch, a camera, a computer, and/or any other mobile device. Mobile device18may include various components that enable it to perform the recited functions. For instance, mobile device18may include a microprocessor, an RF receiver (e.g., an amplitude modulation (AM) receiver, a phase-shift keying (PSK) receiver/demodulator, etc.), and a wireless transceiver (e.g., an 802.11 chipset). Further, in some embodiments, mobile device18may include timestamping circuitry, such as an edge detector configured to detect a rising/falling edge or a zero-crossing (e.g., high-speed comparator), a high-frequency timestamping clock configured to define a master time base (e.g., a 300 MHz cyclical 32-bit counter), and a timestamp latch configured to generate an interrupt signal when each new edge is captured). Further yet, in other embodiments, mobile device18may include an analog-to-digital (A/D) converter configured to capture signal strength samples and generate interrupts at a predefined rate (e.g., 50 MHz). As examples, mobile device18may take the form of a cell phone, a personal navigation device (PND), or a tag. Other configurations of mobile device18are possible as well.

Central server20may be any device configured to receive and store data regarding a location of mobile device18(as well as other mobile devices) within indoor environment22.

Central server20may include various components that enable it to perform these functions. For instance, central server20may include a processor, data storage, and a wireless transceiver (e.g., an 802.11 card). Other configurations of central server20are possible as well.

FIG. 2is a simplified flow chart of an exemplary method30for determining a location of a mobile device within an indoor environment. Fewer or more steps may be provided. For purposes of illustration, exemplary method30will be described with reference to communication system10determining a location of mobile device18within indoor environment22, but it should be understood that exemplary method30may be applicable to other systems as well. In one example, one or more steps of exemplary method30may be embodied as program instructions stored on a non-transitory computer-readable medium and executable by a processor.

As shown inFIG. 2, exemplary method30begins at step32with CSS12driving each of transmitters14A-14Dto output a respective RF signal on a common time basis. In turn, at step34, each of transmitters14A-14Dmay be outputting a respective RF signal on a common time basis.

At step36, mobile device18may be receiving a respective RF signal from each of transmitters14A-14D. In turn, at step38, mobile device18may capture data representing the respective RF signals. At step40, mobile device18may also optionally report the captured data representing the respective RF signals to central server20.

At step42, based on the captured data representing the respective RF signals, mobile device18and/or central server20may discriminate between the respective RF signals and thereby identify which respective RF signal was output by which of transmitters14A-14D. In turn, at step44, mobile device18and/or central server20may calculate a phase shift value of each respective RF signal. At step46, mobile device18and/or central server20may then use the calculated phase shift values and the known location(s) of each of transmitters14A-14Dto determine a location of mobile device18(e.g., a location coordinate and perhaps a geographic coordinate).

At step48, if mobile device18determines its location, mobile device18may also report the determined location to central server20. At step50, central server20may then store the determined location of mobile device18for future reference.

Advantageously, the exemplary location-determination method may enable communication system10to accurately determine and/or track the location of mobile device18. In turn, a location-based service provider may use the determined location of mobile device18to provide a user of mobile device18with location-based services. For example, if mobile device18is located in a store (e.g., a retail store or a grocery store) in which locations are being monitored by communication system10, a location-based service provider may be able to provide a user of mobile device18with an advertisement or coupon relevant to a product in the user's vicinity. Many other examples are possible as well.

III. Embodiments of the Exemplary Location-Determination Method

Embodiments of exemplary method30will now be described. As above, for purposes of illustration, the embodiments of exemplary method30will be described with reference to communication system10determining a location of mobile device18within indoor environment22, but it should be understood that exemplary method30may be applicable to other systems as well.

a. First Embodiment

A first embodiment of exemplary method30begins at step32with CSS12driving each of transmitters14A-14Dto output a respective RF signal on a common time basis and a common carrier frequency in a round-robin manner. For instance, CSS12may be generating a common drive signal that has repeating periods of timeslots, each having at least one timeslot assigned to each of transmitters14A-14Din a round-robin manner and at least one unassigned timeslot. Each timeslot may be occupied by a respective signal segment of the common drive signal. The arrangement of these timeslot periods may take various forms, and may be a known system parameter. In one example, as shown inFIG. 3(a), each period of timeslots of the common drive signal may be arranged to have a first timeslot assigned to transmitter14A, a second timeslot assigned to transmitter14B, a third timeslot assigned to transmitter14c, a fourth timeslot assigned to transmitter14D, and a fifth timeslot that is unassigned. Other examples are possible as well.

Each signal segment may take various forms. For example, each signal segment may take the form of an integral number of cycles (e.g., 64 cycles) of a periodic waveform having a common frequency, such as a sinusoidal wave having a frequency in the long-wave or medium-wave band range (e.g., 148.5 KHz to 283.5 KHz or 520 KHz to 1710 KHz) or a square wave having a frequency in the baseband range (e.g., 5 KHz to 20 KHz). In this respect, CSS12may generate the common drive signal as a continuous waveform. Other examples are possible as well.

To communicate the timeslot assignments to transmitters14A-14D, CSS12may additionally be generating for each of transmitters14A-14Da respective timeslot assignment signal that identifies which timeslots in the common drive signal are assigned to the transmitter. Each such timeslot assignment signal may take various forms. For example, as shown inFIG. 3(b), each timeslot assignment signal may take the form of a bit sequence, with each “1” bit identifying the timeslot in the parallel common drive signal as being assigned to the transmitter and each “0” bit identifying the timeslot in the parallel common drive signal as being assigned to a different transmitter. Other examples are possible as well.

CSS12may then be outputting to each of transmitters14A-14Dthe common drive signal and a respective timeslot assignment signal. In this respect, CSS12may be delaying the output of the common drive signal and a respective timeslot assignment signal to at least one of transmitters14A-14D, to ensure that all of transmitters14A-14Dreceive these signals on a common time basis. For instance, CSS12may be delaying the output of these signals to each of transmitters14A-14Din an amount that is inversely proportional to the length of the transmitter's link (e.g., zero or minimum delay for the longest link and maximum delay for the shortest link). Other examples are possible as well. As a result of CSS12outputting to each of transmitters14A-14Dthe common drive signal and a respective timeslot assignment signal, each of transmitters14A-14Dmay then be receiving the common drive signal and a respective timeslot assignment signal on a common time basis.

At step34, each of transmitters14A-14Dmay be outputting a respective RF signal on a common time basis and a common carrier frequency in a round-robin manner (i.e., only one of transmitters14A-14Dis outputting an RF signal at any one time). For instance, as shown inFIG. 3(c), each of transmitters14A-14Dmay be outputting a segment of the received common drive signal during each of its assigned timeslots as an unmodulated or modulated RF signal on the common carrier frequency. In this respect, as shown, each of transmitters14A-14Dmay stop transmitting before the end of each assigned timeslot, to ensure that its output does not overlap with another transmitter's output. Alternatively, however, each of transmitters14A-14Dmay transmit during the entire duration of each assigned timeslot. In either case, each of transmitters14A-14Dmay enable its power during each of its assigned timeslots (as identified by the timeslot assignment signal) and disable its power during any other timeslot (as identified by the timeslot assignment signal). Other examples are possible as well.

At step36, mobile device18may be receiving a common RF signal on the common carrier frequency that includes a respective RF signal from each of transmitters14A-14D. For instance, mobile device18may be receiving a common RF signal on the common carrier frequency that includes repeating periods of timeslots, each having (a) at least one timeslot occupied by a respective signal segment received from each of transmitters14A-14Din a round-robin manner and (b) at least one unoccupied timeslot. For example, as shown inFIG. 3(d), each period of timeslots of the received common RF signal may have a first timeslot occupied by a signal segment received from transmitter14A, a second timeslot occupied by a signal segment received from transmitter14B, a third timeslot occupied by a signal segment received from transmitter14c, a fourth timeslot occupied by a signal segment received from transmitter14D, and a fifth timeslot that is unoccupied. Further, as shown, the respective signal segments from each of transmitters14A-14Dmay have a phase shift relative to one another due to the differences in transmission times (and thus distances) between each of transmitters14A-14Dand mobile device18. (WhileFIG. 3(d) depicts the timeslots of the received common RF signal as being defined based on the signal segment received from transmitter14A, it should be understood that the timeslots may alternatively be defined based on a signal segment received from one of transmitters14B-14D.) Other examples are possible as well.

At step38, mobile device18may capture data representing the received common RF signal. For instance, mobile receiver18may capture a timestamp of each zero-crossing of the received common RF signal (e.g., for a sinusoidal wave). Alternatively, mobile device18may capture a timestamp of each rising and/or falling edge of the received RF signals (e.g., for a square wave). Other examples are possible as well. At step40, mobile device18may also optionally report the captured data representing the received common RF signal to central server20.

At step42, based on the captured data representing the received common RF signal, mobile device18and/or central server20may discriminate between each respective RF signal that forms the received common RF signal. For instance, based on the captured data representing the received common RF signal, mobile device18and/or central server20may first identify a timeslot of the received common RF signal that is unoccupied (e.g., a time period with a minimal number of captured data points). In turn, mobile device18and/or central server20may identify a beginning of a new period of timeslots immediately following the unoccupied timeslot (e.g., a first captured data point after the time period with no timestamps). Based on the known arrangement of timeslot periods, mobile device18and/or central server20may then discriminate between each respective timeslot in the new period of timeslots and thereby discriminate between each respective signal segment in the new period of timeslots. Further, based on the known arrangement of timeslot periods, mobile device18and/or central server20may identify which respective signal segment was output by which of transmitters14A-14D. Mobile device18and/or central server20may repeat this process to discriminate between each respective timeslot (and each respective signal segment) in each period of timeslots in the received common RF signal. Other examples are possible as well.

After discriminating between each respective timeslot and respective signal segment in the common drive signal, mobile device18and/or central server20may process the data representing the signal segment in each respective timeslot to align the time base of mobile device18with the common time base of transmitters14A-14D. For example, mobile device18and/or central server20may (a) slot the captured data points into modulus buckets, (b) identify the captured data points falling into the most popular modulus, and (c) perform a least squares fit on the identified captured data points to generate an accurate time base. Other examples are possible as well.

At step44, after discriminating between each respective RF signal that forms the received common RF signal, mobile device18and/or central server20may determine a relative phase shift value of each respective RF signal. For instance, in each period of timeslots, mobile device18and/or central server20may first identify one or more captured data points representing each respective signal segment. Further, mobile device18and/or central server20may define one signal segment in the period as a reference signal segment having a relative phase shift value of 0. For each given segment in the period other than the reference segment, mobile device18and/or central server20may then (a) calculate a first time difference between the given segment and the reference segment and (b) calculate a second time difference between the given segment's timeslot and the reference segment's timeslot (e.g., based on the known duration of timeslots). In turn, mobile device18and/or central server20may calculate the relative phase shift of the given segment with respect to the reference segment as the time difference between the first and second calculated time differences. As mentioned above,FIG. 3(d) illustrates the relative phase shift of the respective signal segment received from each of transmitters14B-14Dwith respect to the signal segment received from transmitter14A.

At step46, after determining a relative phase shift value of each respective RF signal, mobile device18and/or central server20may use the relative phase shift values and the known location(s) of each of transmitters14A-14Dto determine a location of mobile device18. For instance, based on the relative phase shift values, mobile device18and/or central server20may first calculate the absolute distances between mobile device18and each of transmitters14A-14Dusing any technique now known or later developed. In turn, based on the absolute distances between mobile device18and each of transmitters14A-14Dand the known location(s) of each of transmitters14A-14D, mobile device18and/or central server20may calculate the location of the mobile device18using any technique now known or later developed (e.g., multilateration). For example, based on the absolute distances between mobile device18and each of transmitters14A-14Dand the known location of each of transmitters14A-14Dwithin indoor environment22, mobile device18and/or central server20may calculate the location of the mobile device18within the indoor environment (e.g., local coordinates). As another example, based on the absolute distances between mobile device18and each of transmitters14A-14Dand the known location of each of transmitters14A-14Dwithin a global environment, mobile device18and/or central server20may calculate the location of the mobile device18within the global environment (e.g., geographic coordinates). Other examples are possible as well.

At step48, if mobile device18determines its location, mobile device18may also report the determined location to central server20. At step50, central server20may then store the determined location of mobile device18for future reference.

b. Second Embodiment

A second embodiment of exemplary method30begins at step32with CSS12driving each of transmitters14A-14Dto output a respective RF signal on a common time basis and a common carrier frequency in a round-robin manner. For instance, CSS12may be generating a common drive signal that has repeating periods of timeslots, each having at least one timeslot assigned to each of transmitters14A-14Din a round-robin manner. Each timeslot may be occupied by a respective signal segment of the common drive signal that includes a header segment and an identifier segment that uniquely identifies the assigned transmitter. The arrangement of the timeslot periods may also have various forms and may be a known system parameter. In one example, as shown inFIG. 4(a), each period of timeslots of the common drive signal may be arranged to have a first timeslot assigned to transmitter14A, a second timeslot assigned to transmitter14B, a third timeslot assigned to transmitter14c, and a fourth timeslot assigned to transmitter14D. Other examples are possible as well.

Each header segment may take various forms. For example, each header segment in the sequence may take the form of an integral number of cycles of a square wave having a frequency in the baseband range (e.g., 5 KHz to 20 KHz). Other examples are possible as well. Each identifier segment in the sequence may also take various forms. For example, each identifier segment may take the form of a bit pattern in which each “1” bit is represented by plurality of cycles (e.g., 5) of a square wave having a frequency in an increased baseband range (e.g., 20 KHz to 100 KHz range) and each “0” bit is represented by a null signal. Other examples are possible as well.

As in the first embodiment, to communicate the timeslot assignments to transmitters14A-14D, CSS12may additionally be generating for each of transmitters14A-14Da respective timeslot assignment signal that identifies which timeslots in the common drive signal are assigned to the transmitter. Each such timeslot assignment signal may take various forms. For example, as shown inFIG. 4(b), each timeslot assignment signal may take the form of a bit sequence, with each “1” bit identifying the timeslot in the parallel common drive signal as being assigned to the transmitter and each “0” bit identifying the timeslot in the parallel common drive signal as being assigned to a different transmitter. Other examples are possible as well.

CSS12may then be outputting to each of transmitters14A-14Dthe common drive signal and a respective timeslot assignment signal. In this respect, as in the first embodiment, CSS12may be delaying the output of the common drive signal and a respective timeslot assignment signal to at least one of transmitters14A-14D, to ensure that all of transmitters14A-14Dreceive these signals on a common time basis. For instance, CSS12may be delaying the output of these signals to each of transmitters14A-14Din an amount that is inversely proportional to the length of the transmitter's link (e.g., zero or minimum delay for the longest link and maximum delay for the shortest link). Other examples are possible as well. As a result of CSS12outputting to each of transmitters14A-14Dthe common drive signal and a respective timeslot assignment signal, each of transmitters14A-14Dmay then be receiving the common drive signal and a respective timeslot assignment signal on a common time basis.

At step34, each of transmitters14A-14Dmay be outputting a respective RF signal on a common time basis and a common carrier frequency in a round-robin manner (i.e., only one of transmitters14A-14Dis outputting an RF signal at any one time). For instance, as shown inFIG. 4(c), each of transmitters14A-14Dmay be outputting a header and identifier segment of the received common drive signal during each of its assigned timeslots as an unmodulated or modulated RF signal on the common carrier frequency. In this respect, as shown, each of transmitters14A-14Dmay transmit during the entire duration of each assigned timeslot. Alternatively, however, each of transmitters14A-14Dmay stop transmitting before the end of each assigned timeslot, to ensure that the transmitter's output does not overlap with another transmitter's output. In either case, each of transmitters14A-14Dmay enable its power during each of its assigned timeslots (as identified by the timeslot assignment signal) and disable its power during any other timeslot (as identified by the timeslot assignment signal). Other examples are possible as well.

At step36, mobile device18may be receiving a common RF signal on the common carrier frequency that includes a respective RF signal from each of transmitters14A-14D. For instance, mobile device18may be receiving a common RF signal on the common carrier frequency that includes repeating periods of timeslots, each having at least one timeslot occupied by a respective header and identifier segment received from each of transmitters14A-14Din a round-robin manner. For example, as shown inFIG. 4(d), each period of timeslots of the received common RF signal may have a first timeslot occupied by a header and identifier segment received from transmitter14A, a second timeslot occupied by a header and identifier segment received from transmitter14B, a third timeslot occupied by a header and identifier segment received from transmitter14c, and a fourth timeslot occupied by a header and identifier segment received from transmitter14D. Further, as shown, the respective signal segments from each of transmitters14A-14Dmay have a phase shift relative to one another due to the differences in transmission times (and thus distances) between each of transmitters14A-14Dand mobile device18. (WhileFIG. 4(d) depicts the timeslots of the received common RF signal as being defined based on the signal segment received from transmitter14A, it should be understood that the timeslots may alternatively be defined based on a signal segment received from one of transmitters14B-14D.) Other examples are possible as well.

At step38, mobile device18may capture data representing the received common RF signal. For instance, mobile device18may capture a timestamp of each rising and/or falling edge of the header and identifier segments. Other examples are possible as well. At step40, mobile device18may also optionally report the captured data representing the received common RF signal to central server20.

At step42, based on the captured data representing the received common RF signal, mobile device18and/or central server20may discriminate between each respective RF signal that forms the received common RF signal. For instance, based on the captured data representing the received common RF signal, mobile device18and/or central server20may first identify the identifier segments of the received common RF signal. Mobile device18and/or central server20perform this identification in various manners. In one example, mobile device18and/or central server20may search for segments of the common drive signal that take the form of a bit pattern in which each “1” bit is represented by plurality of cycles (e.g., 5) of a square wave having a frequency in an increased baseband range (e.g., 20 KHz to 100 KHz range) and each “0” bit is represented by a null signal. These segments may appear to mobile device18and/or central server20as time periods with a large number of captured data points. Other examples are possible as well. Based on these identifier segments and the known arrangement of timeslots, mobile device18and/or central server20may then discriminate between each respective timeslot in the common drive signal and thereby discriminate between each respective signal segment received in the common drive signal.

After discriminating between each respective timeslot and respective signal segment in the common drive signal, mobile device18and/or central server20may process the data representing the header segment in each respective timeslot to align the time base of mobile device18with the common time base of transmitters14A-14D. For example, mobile device18and/or central server20may (a) slot the captured data points into modulus buckets, (b) identify the captured data points falling into the most popular modulus, and (c) perform a least squares fit on the identified captured data points to generate an accurate time base. Other examples are possible as well. In turn, mobile device18and/or central server20may use the aligned time base of mobile device18to accurately determine the pattern of the identifier segment in each respective signal segment, and thus identify which respective signal segment was output by which of transmitters14A-14D. Other examples are possible as well.

At step44, after discriminating between each respective RF signal that forms the received common RF signal, mobile device18and/or central server20may determine a relative phase shift value of each respective RF signal. For instance, in each period of timeslots, mobile device18and/or central server20may first identify one or more captured data points representing each respective identifier segment (e.g., a timestamp of a first rising edge of each identifier segment). Mobile device18and/or central server20may then define one identifier segment in the period as a reference identifier segment having a relative phase shift value of 0. For each given identifier segment in the period other than the reference identifier segment, mobile device18and/or central server20may then (a) calculate a first time difference between the given identifier segment and the reference identifier segment and (b) calculate a second time difference between the given identifier segment's timeslot and the reference identifier segment's timeslot (e.g., based on the known duration of timeslots). In turn, mobile device18and/or central server20may calculate the relative phase shift of the given identifier segment (and thus the given signal segment) with respect to the reference identifier segment (and thus the reference signal segment) as the time difference between the first and second calculated time differences. As mentioned above,FIG. 4(d) illustrates the relative phase shift of the respective signal segment received from each of transmitters14B-14Dwith respect to the signal segment received from transmitter14A.

At step46, after determining a relative phase shift value of each respective RF signal, mobile device18and/or central server20may use the relative phase shift values and the known location(s) of each of transmitters14A-14Dto determine a location of mobile device18. For instance, based on the relative phase shift values, mobile device18and/or central server20may first calculate the absolute distances between mobile device18and each of transmitters14A-14Dusing any technique now known or later developed. In turn, based on the absolute distances between mobile device18and each of transmitters14A-14Dand the known location(s) of each of transmitters14A-14D, mobile device18and/or central server20may calculate the location of the mobile device18using any technique now known or later developed (e.g., multilateration). For example, based on the absolute distances between mobile device18and each of transmitters14A-14Dand the known location of each of transmitters14A-14Dwithin indoor environment22, mobile device18and/or central server20may calculate the location of the mobile device18within the indoor environment (e.g., local coordinates). As another example, based on the absolute distances between mobile device18and each of transmitters14A-14Dand the known location of each of transmitters14A-14Dwithin a global environment, mobile device18and/or central server20may calculate the location of the mobile device18within the global environment (e.g., geographic coordinates). Other examples are possible as well. At step48, if mobile device18determines its location, mobile device18may also report the determined location to central server20. At step50, central server20may then store the determined location of mobile device18for future reference.

A third embodiment of exemplary method30begins at step32with CSS12driving each of transmitters14A-14Dto output a respective RF signal on a common time basis and a different carrier frequency. For instance, CSS12may be generating a separate drive signal for each of transmitters14A-14D, with each drive signal having a different frequency. Each separate drive signals may take various forms. For example, each separate drive signal may be a sinusoidal wave having a frequency in the long-wave band range (e.g., 148.5 KHz to 283.5 KHz). Other examples are possible as well. CSS12will preferably select the different frequencies such that each separate drive signal includes an integral number of cycles during a commonly-defined duration. For example, as shown inFIG. 5, CSS12may generate separate drive signals having frequencies of 250, 225, 200, and 175 KHz respectively, such that each separate drive signal includes an integral number of cycles (10, 9, 8, and 7 respectively) during a 40 microsecond window. Other examples are possible as well.

CSS12may then be outputting a separate drive signal to each of transmitters14A-14D. In this respect, CSS12may be delaying the output of the separate drive signal to at least one of transmitters14A-14D, to ensure that all of transmitters14A-14Dreceive these signals on a common time basis. For instance, CSS12may be delaying the output of the separate drive signal to each of transmitters14A-14Din an amount that is inversely proportional to the length of the transmitter's link (e.g., zero or minimum delay for the longest link and maximum delay for the shortest link). Other examples are possible as well. As a result of CSS12outputting a separate drive signal to each of transmitters14A-14D, each of transmitters14A-14Dmay then be receiving the a separate drive signal on a common time basis.

At step34, each of transmitters14A-14Dmay be outputting a respective RF signal on a common time basis and a different frequency. For instance, each of transmitters14A-14Dmay be outputting its separate drive signal as an unmodulated or modulated RF signal on a respective carrier frequency. Other examples are possible as well.

At step36, mobile device18may be receiving a respective RF signal from each of transmitters14A-14Don a different carrier frequency. For example, mobile device18may receive a first RF signal from transmitter14Aon a first frequency, a second RF signal from transmitters14Bon a second frequency, a third RF signal from transmitter14con a third frequency, and a fourth RF signal from transmitter14con a fourth frequency. Other examples are possible as well.

At step38, mobile device18may capture data representing the respective RF signal from each of transmitters14A-14D. For instance, mobile receiver18may simultaneously capture a signal strength value of each respective RF signal at a given sampling rate (e.g., 50 MHz) during a given duration (e.g., a 44 microsecond window). Other examples are possible as well. At step40, mobile device18may also optionally report the captured data representing the received common RF signal to central server20.

At step42, mobile device18and/or central server20may discriminate between each respective RF signal based on the respective carrier frequency of each respective RF signal. In turn, at step44, mobile device18and/or central server20may determine a relative phase shift value of each respective RF signal. For instance, mobile device18and/or central server20may first fit sine waves to the data representing each respective RF signal (e.g., using a sliding correlator algorithm). Mobile device18and/or central server20may then define one respective RF signal as a reference signal having a relative phase shift value of 0. (Mobile device18and/or central server20may also use the reference signal to align the time base of mobile device18with the common time base of transmitters14A-14D). For each respective RF signal other than the reference signal, mobile device18and/or central server20may then calculate a first phase difference between the respective RF signal and the reference signal and (b) calculate a second phase difference between the respective RF signal's carrier frequency and the reference signal's carrier frequency. In turn, mobile device18and/or central server20may calculate the relative phase shift of the respective RF signal with respect to the reference signal as the difference between the first and second calculated phase differences. Other examples are possible as well.

At step46, after determining a relative phase shift value of each respective RF signal, mobile device18and/or central server20may use the relative phase shift values and the known location(s) of each of transmitters14A-14Dto determine a location of mobile device18. For instance, based on the relative phase shift values, mobile device18and/or central server20may first calculate the absolute distances between mobile device18and each of transmitters14A-14Dusing any technique now known or later developed. In turn, based on the absolute distances between mobile device18and each of transmitters14A-14Dand the known location(s) of each of transmitters14A-14D, mobile device18and/or central server20may calculate the location of the mobile device18using any technique now known or later developed (e.g., multilateration). For example, based on the absolute distances between mobile device18and each of transmitters14A-14Dand the known location of each of transmitters14A-14Dwithin indoor environment22, mobile device18and/or central server20may calculate the location of the mobile device18within the indoor environment (e.g., local coordinates). As another example, based on the absolute distances between mobile device18and each of transmitters14A-14Dand the known location of each of transmitters14A-14Dwithin a global environment, mobile device18and/or central server20may calculate the location of the mobile device18within the global environment (e.g., geographic coordinates). Other examples are possible as well.

At step48, if mobile device18determines its location, mobile device18may also report the determined location to central server20. At step50, central server20may then store the determined location of mobile device18for future reference.

The systems and methods described above are directed to determining a location of a mobile device within an indoor environment. It should be understood, however, that the techniques described herein are not limited to any particular environment, and are thus equally applicable to determining a location of a mobile device in an outdoor or other environment.

The logic, data, software, or instructions for implementing the systems, processes, methods and/or techniques discussed above are provided on computer-readable storage media or memories or other tangible media, such as a cache, buffer, RAM, removable media, hard drive, other computer readable storage media, or any other tangible media. The tangible media include various types of volatile and nonvolatile storage media. The functions, acts, steps, or tasks illustrated in the figures or described herein are executed in response to one or more sets of logic or computer-executable instructions stored in or on computer readable storage media. The functions, acts or tasks are independent of the particular type of instructions set, storage media, processor or processing strategy and may be performed by software, hardware, integrated circuits, firmware, micro code and the like, operating alone or in combination. Likewise, processing strategies may include multiprocessing, multitasking, parallel processing and the like. In one embodiment, the instructions are stored on a removable media device for reading by local or remote systems. In other embodiments, the logic or instructions are stored in a remote location for transfer through a computer network or over telephone lines. In yet other embodiments, the logic or instructions are stored within a given computer, central processing unit (“CPU”), and/or graphics processing unit (“GPU”) or system.

It is intended that the foregoing detailed description be regarded as illustrative rather than limiting and that it is understood that the following claims including all equivalents are intended to define the scope of the invention.