Abstract: Disclosed are systems, methods and devices for computing an estimated location of a mobile device based, at least in part, on an observed difference of time of arrival of messages arriving at the mobile device. In particular implementations, such observed time arrival may comprise a difference between receipt at the mobile device a first message transmitted from a first transceiver device to a second transceiver device and receipt at the mobile device of a second message transmitted by the second transceiver device in response to the first message.

Abstract: Wireless local area networks (WLANs) provide wireless communication between various wireless devices. Frames are acknowledged (ACKed) after a short and predefined MAC idle time. The MAC idle time varies with 1) the physical distance between wireless devices, caused by the delay of wireless signal propagation, and 2) the time to detect the ACK at the local wireless device, which varies with the signal strength of the incoming ACK. Embodiments present CAESAR (CArriEr Sense-bAsed Ranging), which combines time of flight (TOF) and signal-to-noise ratio (SNR) measurements to calculate the distance between two wireless devices. CAESAR measures the distance by estimating the MAC idle time in a data/ACK communication at a particular clock resolution and the ACK detection time on a per-frame basis. Performance measurements confirm the accuracy of the solution and show the capability to track the distance to WLAN smart phones at pedestrian speeds.

Abstract: An electronic apparatus includes a selection unit, a storage unit and a processing unit. The selection unit and the storage unit are coupled to the processing unit. The selection unit selects a first reference point proximate to the electronic apparatus. The storage unit stores a plurality of second locations of a plurality of second reference points. The processing unit executes a single-point distance measurement between the electronic apparatus and a first location of the selected first reference point, provides the electronic apparatus auxiliary positioning information by selecting the second locations stored in the storage unit and generates a speculative location of the electronic apparatus by further computing the results of the single-point distance measurement and the auxiliary positioning information.

Abstract: A method of displaying navigation limits for a planned travel route of a vehicle is presented here. The method calculates estimated navigation limits for the vehicle using an onboard subsystem of the vehicle, where the estimated navigation limits represent self-assessed navigation accuracy of the vehicle relative to the planned travel route. Contracted navigation limits are acquired for the vehicle, where the contracted navigation limits represent specified navigation accuracy of the vehicle, relative to the planned travel route, as mandated by a third party navigation controller. A navigation display is rendered on an onboard display element such that it includes graphical representations of the planned travel route, at least one of the estimated navigation limits, and at least one of the contracted navigation limits.

Abstract: Systems and methods for correcting a location of a terminal are provided. In various aspects, a processor in a position correction apparatus may associate a reference position with the terminal, and determine a range for the terminal based on the reference position. The processor may also associate a second position with the terminal, and determine if the second position associated with the terminal is outside the determined range for the terminal based on the reference position. Upon a determination that indicates that the second position is outside the determined range, the processor may correct the second position to a corrected position associated with the terminal.

Abstract: A method for tracking the object includes providing a motion detector on a first radio frequency device and detecting the motion of the first radio frequency device, transmitting radio frequency location signals from the first radio frequency device to a second radio frequency device with time intervals between the transmissions, decreasing the time intervals between the transmissions from the first radio frequency device to the second radio frequency device in response to the detection of motion by the motion detector, and periodically determining a separation distance between the first radio frequency device and the second radio frequency device based on the radio frequency location signals transmitted from the first radio frequency device to the second radio frequency device.

Abstract: A method and system for locating the position of a source that emits a rotating magnetic field. Three or more receivers are deployed or positioned in known position relative to each other, which may be along a common axis in some cases. Phase differences between the magnetic fields measured by the receivers are detected. The phase shifts are used to determine the location of the source. With three receivers, a range and bearing angle relative to a middle receiver may be determined. With five or more receivers, a range and two bearing angles may be determined, thereby providing a three-dimensional position.

Abstract: Techniques and methodologies are disclosed for minimizing inaccuracies in distance measurements and location determinations for autonomous vehicles or targets ranging to subsets of beacons. Such techniques and methodologies can be used to better control (e.g., navigate) an autonomous vehicle in an area and/or along a pathway, or trajectory.

Abstract: A moving signal receiver determines a plurality of signal receiver positions and corresponding ranges to the moving signal receiver from a first terrestrial transmitter by, while positioned at each of a plurality of distinct positions, determining a position of the moving signal receiver based on signals received from one or more respective sources distinct from the first terrestrial transmitter; and while determining the position of the moving signal receiver, concurrently obtaining a respective range to the moving signal receiver from the first terrestrial transmitter. The moving signal receiver computes a location of the first terrestrial transmitter based on the plurality of signal receiver positions and corresponding ranges.

Abstract: A method for locating wireless devices within a local region, comprising: determining respective global locations of two or more of the wireless devices; determining whether the wireless devices are within the local region by calculating respective distances between the global locations; determining respective ranges between the wireless devices within the local region; and, determining respective relative locations of the wireless devices within the local region by triangulation using the ranges.

Abstract: A method of obtaining an absolute time reference for a high-frequency (HF) sounding signal includes transmitting a reference signal at a first location and transmitting a sounding signal in close proximity to the transmitting of the reference signal at the first location. The method additionally includes receiving the reference signal at a second location and receiving the sounding signal at the second location. The method further includes determining a relative delay at the second location of the sounding signal in relation to the reference signal. The method also includes determining a propagation mode based upon the relative delay. The method additionally includes determining an absolute time reference based upon the propagation mode being observed. Additional methods and associated systems for implementing the methods are also provided.

Abstract: Techniques and methodologies are disclosed for minimizing inaccuracies in distance measurements and location determinations for autonomous vehicles or targets ranging to subsets of beacons. Such techniques and methodologies can be used to better control (e.g., navigate) an autonomous vehicle in an area and/or along a pathway, or trajectory.

Abstract: An application executed within a mobile station to be triggered only by a network element, such as a mobile positioning center (MPC) or a Mobile Center (MC). The network element is coupled to a base station. The network element is responsible for authorizing an application that is either resident within the mobile station or that is run in a device that is resident elsewhere in the network. The mobile station communicates with the network element over a communication link through the base station and other infrastructure components. The mobile station will only respond to attempts to trigger particular operations (e.g., run particular applications) if the mobile station receives a short message services (SMS) message as defined by Interim Specification 637A (IS-637A) which is published by the Telecommunication Industry Association (TIA)/Electronics Industry Association (EIA). More specifically, that SMS message must include an SMS Teleservice Identifier that has a particular pre-assigned value.

Abstract: Embodiments of the present invention include a method of determining a location of a mobile device. The method comprises transmitting a signal between a plurality of known locations and receiving signal at device of unknown location such as a mobile device. The signal may include multiple tones having different frequencies and resulting in sets of residual phase differences. The location of the mobile device may be determined using the known locations and the frequency and phase differences between the transmitted tones. In one embodiment, OFDM signals may be used between an access point and mobile device, for example, to determine the location of the mobile device.

Abstract: Various methods, systems, and computer program products are disclosed for determining a location estimate of user equipment in a mobile network. For example, a method may include receiving measurement data that includes a time of arrival indication of data communicated between the user equipment and base stations of the mobile network. The method may further include processing only the received measurement data that is within a particular time window and excluding some of the received measurement data outside the particular time window. The method may further include determining a sync value based on the received measurement data within the time window. The sync value may synchronize timing between at least two base stations of the mobile network. The method may include determining a location of the user equipment based on the sync value and the measurement data. The method may include geometric or linear optimization of the determined location estimate.

Abstract: A wireless medical device is disclosed. The wireless medical device comprises a processor, a memory, a sensor for detecting a physiological signal, a radio and a proximity detector to measure a distance of the wireless medical device relative to a second wireless medical device. The proximity detector includes a ranging functionality. A wireless communication channel is created when a distance between the wireless medical device and the second wireless medical device is within a first predetermined threshold. The distance is greater than zero.

Abstract: A vehicle can be controlled in a first autonomous mode of operation by at least navigating the vehicle based on map data. Sensor data can be obtained using one or more sensors of the vehicle. The sensor data can be indicative of an environment of the vehicle. An inadequacy in the map data can be detected by at least comparing the map data to the sensor data. In response to detecting the inadequacy in the map data, the vehicle can be controlled in a second autonomous mode of operation and a user can be prompted to switch to a manual mode of operation. The vehicle can be controlled in the second autonomous mode of operation by at least obtaining additional sensor data using the one or more sensors of the vehicle and navigating the vehicle based on the additional sensor data.

Abstract: The invention relates to a method for the position determination of objects (62, 707,84, 96) by means of communication signals, in which a transceiver capable of wireless communication transmits communication signals, the transceiver (51) being capable of simultaneous transmission and reception, and wherein the communication signals are at least partially reflected as reflection signals on at least one object (62, 707, 84, 96) in a signal propagation zone and the transceiver (51) receives the reflection signals. The method is characterized in that phase information of the reflection signals or communication signals are determined. The invention further relates to a corresponding device and to a use of the device.

Abstract: A handheld terminal that makes it easy to identify the position of a locator. Said handheld terminal (100) is provided with the following: a wireless unit (130) that receives a radio signal transmitted by the locator; an RSSI detection unit (150) that measures the strength of the received radio signal; a distance-information determination unit (211) that, on the basis of the measured received signal strength, determines distance information that indicates a distance level between the wireless unit (130) and the locator; and an annunciation unit (240) that outputs the determined distance information.

Abstract: A method and a system for storing a constant path loss exponent corresponding to free space; transmitting a signal; receiving the signal via a rake receiver of a user device; identifying a maximum received signal strength based on a signal strength associated with the signal relative to fingers of the rake receiver; storing a current maximum received signal strength value; determining whether the current maximum received signal strength value is a first maximum received signal strength value; calculating a current indoor position of the user device based on the constant path loss exponent and the current maximum received signal strength value when a determination is that the current maximum received signal strength value is the first maximum received signal strength value; and outputting the current indoor position.

Abstract: In a two-way ranging scheme where a first apparatus (e.g., device) determines a distance to a second apparatus (e.g., device), specified packets are sent between these apparatuses at specified times to facilitate the determination of the distance. In some aspects, these packets may be defined and/or sent in a manner that enables the apparatuses to detect a leading edge of a received packet with a high degree of accuracy. For example, an apparatus may transmit a packet a defined period of time after transmitting or receiving another packet. In addition, a packet may comprise a defined symbol sequence that is used by an apparatus that receives the packet to identify a leading edge of the packet.

Abstract: According to this embodiment, a position estimating device, that estimates a position of a target wireless device, includes a storage that stores positions of a plurality of reference wireless devices, a receiver which is notified of a received signal strength indicator value in signal transmission and reception between the target wireless device and each reference wireless device, a calculator that calculates a standard deviation for a probability distribution of a distance between the target wireless device and each reference wireless device, using the received signal strength indicator value, a first estimator that calculates an estimated distance between the target wireless device and each reference wireless device, using the received signal strength indicator value, and a second estimator that calculates the position of the target wireless device, using the standard deviation, the estimated distance, and the positions of the plurality of reference wireless devices.

Abstract: Methods and systems are described for using location-based information to determine whether to perform a ranging procedure. A change in location of a device is identified. The identified change in location represents the distance the device has moved during an interval between ranging procedures. The identified change in location is analyzed to determine whether the change exceeds a threshold distance. If the change in location does not satisfy the threshold distance, a change in a signal quality metric of the device from the location associated with the previously performed ranging procedure to the current location is identified. The identified change in signal quality metric is analyzed to determine whether the change exceeds a threshold value. If the change in location of the device is less than the threshold distance and the change in the signal quality metric is less than the threshold value, the next scheduled ranging procedure is bypassed.

Abstract: A user equipment (36) herein resolves timing ambiguities associated with when the user equipment (360 is to perform assisted positioning measurements. The user equipment (36) receives assistance data that indicates positioning occasion periodicities of a first cell and a reference cell, and that indicates a positioning occasion timing offset between those cells. The user equipment (36) performs signal detection at candidate timing offsets surrounding the indicated positioning occasion timing offset, to determine which candidate timing offset has the greatest probability of being the actual positioning occasion timing offset between the first cell and the reference cell. The user equipment (36) may then time assisted positioning measurements for the first cell based on the candidate timing offset determined as most likely being the actual timing offset, rather than necessarily timing those measurements based on the offset indicated in the assistance data.

Abstract: Described are systems and methods for estimating error associated with one or more range measurements that are used to estimate the position of a receiver. Estimations of range error may be based on surveyed range errors for nearby position estimates. Estimations of range error may alternatively be based on comparisons of actual movement of a receiver to estimated movement between two position estimates.

Abstract: Described are systems and methods for estimating a position of receiver using ranging signals from different regions in a network of transmitters. In some embodiments, each ranging signal that exceeds a quality criterion is assigned to one of several defined regions based on a characteristic of that ranging signal. A maximum number of ranging signals per region may be selected and used during trilateration.

Abstract: Described are systems and methods for identifying transmitters that adversely affect a trilateration result.

Abstract: In a two-way ranging scheme where a first apparatus (e.g., device) determines a distance to a second apparatus (e.g., device), specified packets are sent between these apparatuses at specified times to facilitate the determination of the distance. In some aspects, these packets may be defined and/or sent in a manner that enables the apparatuses to detect a leading edge of a received packet with a high degree of accuracy. For example, an apparatus may transmit a packet a defined period of time after transmitting or receiving another packet. In addition, a packet may comprise a defined symbol sequence that is used by an apparatus that receives the packet to identify a leading edge of the packet.

Abstract: System and methods are disclosed to use ultrasonic (US) and WiFi signals to improve range determination between devices in WiFi-based position or range estimation systems. Such systems may leverage existing WiFi infrastructure and US-capable sensors such as speakers and microphones as US transducers. US ranging between devices may be performed using round-trip time (RTT) or one-way measurements. To enable US ranging between a device and multiple US transmitters simultaneously, the US signal from each US transmitters or from the device may be modulated with a unique pseudo-random number (PRN) using direct sequence spread spectrum (DSSS). The transmission of US signals may be synchronized with the transmission of WiFi beacons which may contain data fields that contain the PRN sequence used to modulate the synchronous US signal. In RTT ranging, a receiving device receiving an US signal transmission may respond with its own PRN-modulated US signal synchronized to its WiFi beacon.

Abstract: Methods, systems, and devices are described for tracking an asset or person using a synchronized set of anchor units. A tag attached to the asset or person has a clock offset relative to the anchor units, which in turn have clock offsets relative to each other. To remove the effect of the clock offset from the tag when estimating the location of the tag, the anchor units are synchronized by determining their clock offsets through signals wirelessly transmitted between the anchor units. The clock offsets may be obtained when there is a clear line-of-sight (LOS) path between anchor units as well as when the LOS path is obstructed. The range measurements that produce the estimate of the location of the tag are then determined from preamble information provided by the tag and from the clock offsets determined for the anchor units.

Abstract: A positioning and ranging system includes a transmitter transmits a plurality of impulses; and a receiver receives the impulses; the receiver includes an initial detection unit records a sensing time of a first impulse among a plurality of impulses transmitted by the transmitter; a sensing margin detection unit for detecting a sensing margin being a difference between a field intensity of the first impulse and a reception limit field intensity of the receiver; a correction unit identifies a sensing error differential time based on a given relationship between the sensing margin and the sensing error differential time, and corrects the sensing time detected by the initial detection unit using the identified sensing error differential time; the system measures a distance between the transmitter and the receiver and a position of the transmitter based on a time the transmitter transmits the first impulse and a time the receiver receives the impulse.

Abstract: Embodiments enable geofencing applications and beacon watch lists. A computing device with at least a first processor and a second processor identifies a set of beacons associated with a geofence. The first processor consumes less power when operating than the second processor. The first processor is provided with the identified set of beacons. In beacon watch list embodiments, the first processor detects one or more beacons proximate to the computing device, compares the detected beacons with the provided set of beacons to determine whether the computing device is within the geofence, and updates a location status based on the comparison. In tiered geofencing implementations, the computing device switches among positioning modalities based on a distance from the computing device to the geofence to save power.

Abstract: The proposed solution includes the use of four reference bases on the ground at known positions, with a coded time signal transmitted by one of them which is retransmitted by the repeater station and received by each of the reference bases. Using two distinct sets of three reference bases it is possible to calculate the differences between two positions for the repeater station, assigning to the later changes in time, phase or frequency as well as temporal changes due to the signal propagation in the medium, for the respective elevation angles found for the repeater. It can be then identified which values attributed to the temporal changes produces a minimum difference between the two respective positions of the repeater station. The identified temporal change can be used for the correct determination of the repeater station and its use on pertinent applications.

Abstract: A system and method for estimating the position of an object, such as a person, animal, or machine. The system includes first and second inertial measurement units, a first and second originator antennas, and a first and second transponder antennas. The system uses data from the inertial measurement units to estimate a position of the object. The system also calculates a range measurement between the first originator antenna and first transponder antenna. The system calculates a first CPD measurement between the second transponder antenna and the first originator antenna, and a second CPD measurement between the second originator antenna and the first transponder antenna. The range measurement and at least one CPD measurement are used to update a Kalman filter for estimating the position of the object. The system determines also updates the Kalman filter when one of the inertial measurement units is in a zero-velocity condition.

Abstract: A RF tag reader may use spatial averaging to compensate for the limitations of performing multi-frequency continuous-wave ranging (MFCW) in a bandwidth-limited environment. Although MFCW provides an estimate of the separation distance between a RF tag and the tag reader with errors that vary widely, the error values form a pattern based on the separation distance. That is, as the separation distance increases or decreases, the error values oscillate between maximum and minimum values centered on the correct separation distance. Accordingly, in one embodiment, the receiver uses spatial averaging to average out this oscillating error (e.g., the maximum errors are counter-balanced by the minimum errors). The more accurate, spatially-averaged MFCW estimate may then be used to resolve the cycle ambiguity in continuous-wave ranging to identify the separation distance between the RF tag and the tag reader.

Abstract: System and method for traffic mapping service are disclosed for allowing plurality of users having each a navigation device to transmit their locations to a server and optionally to signal to the server their requested destination. The system and method are further capable of calculating traffic parameters such as current traffic speed at a given road based on the momentary locations of the users. The system and method of the invention may also calculate and advise the users of preferred roads to take in order to arrive at the requested location with minimum delay.

Abstract: Embodiments of the present invention include a method of determining a location of a mobile device. The method comprises transmitting a signal between a plurality of known locations and receiving signal at device of unknown location such as a mobile device. The signal may include multiple tones having different frequencies and resulting in sets of residual phase differences. The location of the mobile device may be determined using the known locations and the frequency and phase differences between the transmitted tones. In one embodiment, OFDM signals may be used between an access point and mobile device, for example, to determine the location of the mobile device.

Abstract: A method and apparatus are disclosed for reducing traffic flow instabilities and increasing vehicle throughput by monitoring the distances and velocities of motor vehicles leading and following a center vehicle and controlling the velocities of the vehicles to maintain a steady relative distance between the center vehicle and the leading and following vehicles. Using distance and speed information derived from both leading and following vehicles reduces the loop gain of feedback needed below one (1) and diminishes traffic instabilities caused by “car following.

Abstract: A data processing method and a data re-transmission method in a broadband wireless access system are disclosed. A transmitting side generates a coded block set including coded blocks of a predetermined number and the coded blocks are transmitted to first and second base stations. The transmitting side sets a timer after transmitting a last coded block of the coded blocks. The coded blocks received by the second base station are transmitted to the first base station, and the transmitting side receives a control signal indicating whether there is a transmission error from the first base station.

Abstract: Systems and methodologies are described herein that facilitate Hybrid Automatic Repeat Request (H-ARQ) scheduling and coordination in a wireless communication system. As described herein, a network node capable of cooperation with other nodes for communication to respective users can coordinate a cooperation strategy across nodes based on a H-ARQ protocol to be utilized for a given user. In the case of a synchronous H-ARQ protocol, communication can be scheduled as described herein such that initial transmissions to a user are conducted cooperatively and re-transmissions are conducted without inter-node cooperation. In the case of a H-ARQ protocol utilizing persistent assignments, transmission intervals can be calculated and utilized based on application latency requirements, backhaul link latency, or other factors.

Abstract: A system and method for delivering content within a boundary is described. The system includes a plurality of beacons, a location positioning module, and a networked component. The beacons transmit a signal containing identifying information. The location positioning module receives the beacon signal data communication from a wireless device. The location positioning module receives measured reference points that include a measured beacon identifier and a measured signal strength. The location positioning module uses the measured reference points to generate calculated signal strength values for at least one detected beacon, wherein some of the calculated signal strength values are associated with a geographic boundary. The location positioning module determines the location of the wireless device by comparing the beacon signal data to the calculated signal strength values.

Abstract: The invention relates to methods and systems for accurate ranging and geo-locationing using coherent multicarrier (CM) signals and based on a high-resolution estimation of a receiver timing offset in a signal receiver that receives ranging CM signals. A transmitter transmits a ranging CM signal having a known subcarrier modulation pattern. The receiver samples the ranging CM signal it receives reflected back from an object or from the remote transmitter, and processes the sampled signal that preserves relative subcarrier phases using a high-resolution model channel response function to determine the receiver timing offset with resolution much better than the receiver sampling period. The receiver timing offset is used to determine a flight time for the ranging CM signal with high accuracy.

Abstract: A collision determination ECU (1) includes: a first information generation section (101) that acquires time information from a timer (4) every predetermined time period PA, and associates own vehicle time information representing an own vehicle time, which is the acquired time information, with own vehicle identification information, to thereby generate first output information; a transmission control section (102) that transmits the generated first output information by broadcasting; a reception control section (103) that receives own vehicle time information representing an own vehicle time and own vehicle identification information, which are included in first output information from an other vehicle VCB, as other vehicle time information representing an other vehicle time and other vehicle identification information, respectively; a reception time acquisition section (104) that acquires reception time information representing a reception time from the timer (4), when the first output information is receiv

Abstract: A system including a first wireless device and a second wireless network device. The first wireless network device is configured to transmit a data frame a first number of times, wherein the first number of times is determined based on a timing resolution associated with the first wireless network device, receive a respective acknowledgement frame in response to each transmission of the data frame, determine an accumulated delay period corresponding to a total time between each transmission of the data frame and reception of the respective acknowledgement frame, and calculate a distance between the first wireless network device and the second wireless network device based on the accumulated delay period and the first number of times. The second wireless network device is configured to receive each transmission of the data frame and transmit the respective acknowledgement frame in response to each transmission of the data frame.

Abstract: A mobile construction device sensor unit system is disclosed. In one embodiment, a point-to-point radio ranging system coupled with a mobile construction device. A position determining component coupled with the point-to-point radio ranging system is configured for determining a position of the sensor unit in at least two dimensions based on communications between the point-to-point radio ranging system and a plurality of tags respectively located at a plurality of knowable locations within an operating environment of the mobile construction device. A communications link controller communicatively coupled with the position determining component is configured for wirelessly providing information, including the sensor unit position, to a receiving unit located apart from the sensor unit.

Abstract: A vehicle can be controlled in a first autonomous mode of operation by at least navigating the vehicle based on map data. Sensor data can be obtained using one or more sensors of the vehicle. The sensor data can be indicative of an environment of the vehicle. An inadequacy in the map data can be detected by at least comparing the map data to the sensor data. In response to detecting the inadequacy in the map data, the vehicle can be controlled in a second autonomous mode of operation and a user can be prompted to switch to a manual mode of operation. The vehicle can be controlled in the second autonomous mode of operation by at least obtaining additional sensor data using the one or more sensors of the vehicle and navigating the vehicle based on the additional sensor data.

Abstract: A signal receiver receives a time-domain signal that includes a plurality of pilot tones at a plurality of corresponding frequencies. The time-domain signal is transmitted from a transmit location. The signal receiver extracts from the received time-domain signal pilot phase values corresponding to the pilot tones. The signal receiver computes a signal propagation time of the received time-domain signal by fitting an interpolation function to residual pilot phase values, corresponding to the extracted pilot phase values, and determines a slope of the interpolation function. The signal receiver computes a range between the transmit location and the signal receiver by multiplying the computed signal propagation time with the speed of light.

Abstract: This invention relates to methods and devices for channel identification. The invention is particularly concerned with techniques for non-line of sight channel identification. In embodiments of the invention the methods and devices are used for channel identification in wireless geolocation systems. Embodiments of the invention make use of an entropy estimation of the channel to distinguish channel conditions and in particular to identify line-of-sight and non-line-of-sight channels and which can be used to solve the NLOS problem of determining relative distances between transmitter and receiver. In particular embodiments an entropy estimation of the channel impulse response (CIR) is used to construct a robust entropy-based channel identification technique. As a result, more accurate localization in indoor and other multipath environments may be possible.

Abstract: A device and method for determining a distance and/or orientation of a movable object includes a transmitter that is located on the object and a receiver. One of the transmitter and the receiver has an antenna having a known polarization plane. The other of the transmitter and the receiver has a counterclockwise circular polarized antenna and a clockwise circular polarized antenna.

Abstract: Communication between a remote locator and a transponder is used to determine the relative position of the transponder. The transponder and locator each include a transmitter and a receiver. The locator transmits an inquiry in the form of a relatively powerful cyclically encoded signal with repetitive elements, uniquely associated with a target transponder. Periodically, each transponder correlates its coded ID against a possible inquiry signal, determining frequency, phase and framing in the process. Upon a match, the transponder transmits a synthesized response coherent with the received signal. The locator integrates multiple cyclical response elements, allowing low-power transmissions from the transponder. The locator correlates the integrated response, determines round-trip Doppler shift, time-of-flight, and then computes the distance and angle to the transponder. The transponder can be wearable, bionically implanted, or attached to, or embedded in, some object.