WO1996042020A2 - Enhanced position calculation - Google Patents
Enhanced position calculation Download PDFInfo
- Publication number
- WO1996042020A2 WO1996042020A2 PCT/US1996/009012 US9609012W WO9642020A2 WO 1996042020 A2 WO1996042020 A2 WO 1996042020A2 US 9609012 W US9609012 W US 9609012W WO 9642020 A2 WO9642020 A2 WO 9642020A2
- Authority
- WO
- WIPO (PCT)
- Prior art keywords
- radio signal
- signal
- received
- radio
- unknown position
- Prior art date
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Classifications
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04W—WIRELESS COMMUNICATION NETWORKS
- H04W64/00—Locating users or terminals or network equipment for network management purposes, e.g. mobility management
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
- G01S1/00—Beacons or beacon systems transmitting signals having a characteristic or characteristics capable of being detected by non-directional receivers and defining directions, positions, or position lines fixed relatively to the beacon transmitters; Receivers co-operating therewith
- G01S1/02—Beacons or beacon systems transmitting signals having a characteristic or characteristics capable of being detected by non-directional receivers and defining directions, positions, or position lines fixed relatively to the beacon transmitters; Receivers co-operating therewith using radio waves
- G01S1/022—Means for monitoring or calibrating
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
- G01S1/00—Beacons or beacon systems transmitting signals having a characteristic or characteristics capable of being detected by non-directional receivers and defining directions, positions, or position lines fixed relatively to the beacon transmitters; Receivers co-operating therewith
- G01S1/02—Beacons or beacon systems transmitting signals having a characteristic or characteristics capable of being detected by non-directional receivers and defining directions, positions, or position lines fixed relatively to the beacon transmitters; Receivers co-operating therewith using radio waves
- G01S1/022—Means for monitoring or calibrating
- G01S1/026—Means for monitoring or calibrating of associated receivers
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
- G01S5/00—Position-fixing by co-ordinating two or more direction or position line determinations; Position-fixing by co-ordinating two or more distance determinations
- G01S5/0009—Transmission of position information to remote stations
- G01S5/0081—Transmission between base stations
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
- G01S5/00—Position-fixing by co-ordinating two or more direction or position line determinations; Position-fixing by co-ordinating two or more distance determinations
- G01S5/02—Position-fixing by co-ordinating two or more direction or position line determinations; Position-fixing by co-ordinating two or more distance determinations using radio waves
- G01S5/0205—Details
- G01S5/021—Calibration, monitoring or correction
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
- G01S5/00—Position-fixing by co-ordinating two or more direction or position line determinations; Position-fixing by co-ordinating two or more distance determinations
- G01S5/02—Position-fixing by co-ordinating two or more direction or position line determinations; Position-fixing by co-ordinating two or more distance determinations using radio waves
- G01S5/0252—Radio frequency fingerprinting
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
- G01S5/00—Position-fixing by co-ordinating two or more direction or position line determinations; Position-fixing by co-ordinating two or more distance determinations
- G01S5/02—Position-fixing by co-ordinating two or more direction or position line determinations; Position-fixing by co-ordinating two or more distance determinations using radio waves
- G01S5/14—Determining absolute distances from a plurality of spaced points of known location
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
- G01S5/00—Position-fixing by co-ordinating two or more direction or position line determinations; Position-fixing by co-ordinating two or more distance determinations
- G01S5/02—Position-fixing by co-ordinating two or more direction or position line determinations; Position-fixing by co-ordinating two or more distance determinations using radio waves
- G01S5/14—Determining absolute distances from a plurality of spaced points of known location
- G01S5/145—Using a supplementary range measurement, e.g. based on pseudo-range measurements
Definitions
- TITLE ENHANCED POSITION CALCULATION FIELD OF INVENTION
- This invention relates to life safety systems where a radio transmitter broadcasts from an unknown location, the unknown location can be estimated using a set of receivers and a signal processing network designed using a neural network or an associative memory
- Applications include personal safety from assault or medical causes roadside assistance, child monitoring for kidnapping recovery, monitoring of the elderly to reduce walk aways, drug enforcement, early release or parolee monitoring, as well as stolen vehicle or stolen equipment recovery
- the unknown position radio transmitter broadcasts a signal that reflects off of objects, such as buildings or buses, before arriving at a series of receivers These reflections cause several versions of the same signal, delayed by different amounts depending on the number of reflections incurred, to be superimposed with one another This distorts the transmitted signal and, if uncorrected, prevents reception and processing of the signal
- Present systems include inherent drawbacks, such as continual monitoring, which require full time surveillance operation or GPS services which require physically larger units with short battery lives and which must operate outdoors in reasonably good view of several satellites Stanford Telecom, in "RF Design", October 1992, teaches the use of signal averaging to reduce multi-path errors 'The tracking error
- the applications require physically small devices, long battery life, and imply transmit-only operation. Successful operation is mandatory, even in a heavily radio frequency shielded environment such as a multi-story high-rise building.
- a ground-based platform In order to increase the Signal-to-Noise Ratio available to a system receiver from a system transmitter whose operation is constrained to the preceding conditions, it is desirable to locate the receiver on a ground-based platform as opposed to an orbital one.
- the ground-based receiver platform does have a disadvantage due to a fairly complex radio wave travel path from the system transmitter (multi-path signal distortion).
- Urban and suburban multi-path distortion may be quite severe, as it's cause increases dramatically with each new object inserted into the path from system transmitter to system receiver (i.e. buildings, vehicles, structures) .
- Delay Spread Profile The analysis of how a particular environment will induce multi-path distortion is called a "Delay Spread Profile”. Delay spread profile analysis shows multi-path echoes on the order of one to five microseconds are not uncommon in urban and suburban environments. Delay spreads of this magnitude cause one thousand feet to one mile potential error to a transmitter's calculated position if error removal tactics are not employed.
- a first object of the invention is to overcome the problems of the prior art discussed above.
- the second object is to achieve a position fix accuracy and reliability appropriate for life safety applications.
- a third object of the invention is to locate a low Signal-to-Noise Ratio transmission with increased accuracy.
- a further object of the invention is to be able to locate a transmitter which is located inside of a multi-story building. This process may be further aided by the employment of a search team equipped with a mobile reference unit.
- a further object of the invention is to remove position fix errors which result from fixed obstacles.
- Another object of the invention is to remove errors from mobile obstacles. This requires either additional receivers or the ability to employ time diversity.
- a further object of the invention is to correct drift errors which result from imperfect time references contained within the various system elements as well as to provide a point or points of common synchronization for the computation of Relative Time-of-Arrival readings.
- a further object of the invention is to learn the signature of an area or areas frequented by a user to increase the accuracy of a position fix made at a future time in that same location
- a further ob j ect of the invention is to provide intelligent averaging or weighing of previous position fixes in order to further enhance the accuracy of the most recent position fix
- Another object of the invention is to provide cues appropriate to guide a search team equipped with a mobile reference unit to find a transmitter of unknown position All radio location systems must provide at least two major functions ( 1 ) to accurately determine a first arriving radio signal or to determine some appropriate attribute of a radio signal which can be used to determine a transmitter's position, (2) computational techniques which are appropriate to convert the information gained into useful position fix information which typically includes latitude, longitude and altitude
- the instant invention is intended to increase the accuracy of a radio location system though computational means which is located at some central receiving site.
- the inputs to these enhanced calculation devices/methods can be any one of a number of position determination measuring techniques.
- Time-of-Arrival information or Relative Time-of-Arrival information can be derived from chirp spread spectrum, pulsed radio, a combination of waved shaped pulse with phase information, phase information from a sin wive with no wave shaping, or by the correlation either serial or parallel of a direct sequence spread spectrum transmission.
- multiple antennas can be used to establish the X, Y, Z phase of a received H field or E field signal.
- phase antennas such as VOR may also be Employed.
- the invention and techniques described herein may also be employed to enhance the position location accuracy of cellular type radio systems by the use of the amplitude, phase, and antenna quadrant information available. Further, any combination of the above techniques may be used to further enrich the information available to the computational elements disclosed herein. All of the techniques disclosed herein can benefit from an initial training session, although the training session may actually be accomplished during the system's normal operation.
- One such training session consists of driving a vehicle around a city or suburban area or area of coverage interest. Such vehicle would be equipped with a reference transmitter.
- the vehicle would be equipped with a technique, or techniques, capable of independently establishing the accurate location of the vehicle.
- the so equipped vehicle would communicate both independent position information as well as beacon transmissions capable of being measured by the radio location system's distributed receivers.
- This training information could be used to create table or matrix lockup correction factors or to establish the appropriate weighing coefficients in a neural network.
- This information could be collected and used in real time or appropriately post processed by any one of the neural network training techniques as shown in the art.
- Such neural network training techniques include, but are not limited to, back propagation, recurrent back propagation, probabilistic neural network, learning vector quantization and k-means clustering. In addition to the either initial or ongoing training, other specific training may be employed.
- a user of the radio location service who carries a UPX on their person may either initially or periodically call into a central station operator or to a voice command-type system. At that time, the user may verbally or numerically indicate his or her physical location at that time. The user whould then initiate a sequence of transmissions on their UPX. The user may stand in one position or may walk in a slow circle in order to enrich the variety of resulting position fixes received by the central monitoring processor.
- the UPX may be equipped with a small radio receiver or a local H-field receiver. Upon the UPX receiving a properly coded message, the UPX may automatically invoke a training burst of transmissions.
- the initiating devices may be located in the user's office or if the UPX used is affixed to an inanimate object, the initiating device may be located in a known or a suspected path of the UPX travel
- the initiating device may be encoded with information relating to latitude, longitude and altitude so that the central processing can associate with this "known" information with the position fixes directly resulting from the initiating device's forced training burst sequence Either of these techniques may be used to establish an electronic "fingerprint" of likely UPX locations which require a high degree of accuracy in subsequent position fix calculations
- fixed references may be installed in part or all of the coverage area These fixed references would either transmit their known latitude, longitude, altitude position or transmit their ID which would later be associated with known latitude, longitude, altitude information in some central database Further, these fixed references may be made a portion of the receiving unit's which are distributed across a city or coverage area These fixed references may be at similar altitudes, but would benefit from being held at various altitudes
- the last M position fixes of a particular UPX may further be used as input to the neural network's matrix.
- the neural network may take advantage of the past M readings in order to enhance the position fix accuracy of the most recent received transmission.
- the position fix processor will input either Relative Time-of-Arrival or Time-of-Arrival or time difference information from each of the receivers obtaining a message from a particular UPX.
- the receivers may also provide signal-to- ⁇ oise ratio information and antenna quadrant information. Receivers may be outfitted with four or eight directional antennas.
- any one or several of the four or eight receivers may provide valuable radio location information to the position fix processor.
- the use of an error correction table, a matrix lockup technique, or the use of neural network processing techniques will increase the accuracy of the position fixes generated. This means that signals received or signal-to-noise ratio may still be adequate to provide the services as contemplated herein.
- the ability to work with low signal-to-noise ratio signals will facilitate the use of more distant receiver sites and enriched information gathered from receiver sites more distant than a first ring constellation of receivers. Using low signal-to-noise ratios also provides the ability to locate a transmitter deep within a multi-story building.
- a typical home may represent approximately 10 dB of signal attenuation at 900 MHz.
- a multi-story building can easily cause 30 dB of signal attenuation. This attenuation must be either overcome by transmitted power, closer receiver sites, reduced information bandwidth, or longer transmissions, making the position fix processor tolerant of poor and noisy signals, or any combination of these techniques.
- Multi-path/obstacle removal may be accomplished by the processor methods disclosed herein and fall into two categories: 1) fixed obstacle and 2) mobile obstacles.
- a fixed obstacle is a large building or structure that will cause a multi-path reflection which is repeatable over some long period of time.
- the initial training sessions isolate these anomalous added paths and adapt them to the neural network or error correction matrix or table.
- the added path and error term actually becomes useful information to enhance the accuracy of the position fix calculation.
- Mobile obstacles are compensated for by direct tactics. One of three tactics may be employed to reduce the errors from such obstacles. Additional receivers may be used such that a receiver suspected of a multi-path error may be eliminated from a position fix calculation such as a least squares fit.
- the network may automatically discount or proportionally reduce the weighing of the input from a suspect receiver. If a mobile obstacle moves in a relatively short period of time then time diversity may be employed. In this case, if a particular reading is suspect or error due to a mobile obstacle, a method seeks to obtain further position fix readings which may be unaffected by the mobile obstacle.
- multi-path errors short or long, can only increase the apparent time of flight/TOA/RTOA readings since the multi-path error is caused from a reflection which causes the 1 traveled path to be longer than the geometric point-to-point path.
- the position processor means may be implemented using a neural network, a correction factor
- Additional methods must be provided to correct multi-path S errors if a UPX is located in between two or more matrix points, or in between the two most likely table 0 lockup points.
- additional interpolation can be used to enhance position calculation 1 accuracy.
- Interpolation algorithms include linear interpolation, linear approximation, linear regression 2 simultaneous equations, a system of differential equations, or the like. 3
- the neural network will directly yield outputs including latitude, longitude and altitude.
- the 4 matrix lockup or table lockup must input to other position calculation algorithms as are known in the art. 5 These include triangulation, multi-lateration, least squares fit algorithms and the like.
- the remainder of the nearby phase repeaters can be made more sensitive through a windowing 8 function, provided that the UPX transmits on a sleep interval pattern which is known to the necessary 9 system elements.
- the chip position would also be known within one or several chips 0 which could be used to lower the amount of search time required by other receivers, and hence 1 subsequently increase the available dwell time and therefore increase signal-to-noise ratio.
- the other receivers would not have to 3 perform frequency searches and/or may further reduce their I.F. bandwidth.
- the first arriving signal in a time of flight radio location system yields the most accurate position fix.
- This first arriving signal leads a complex pattern of signal peaks and valleys called a delay spread profile.
- a typical delay spread profile has multiple peaks within its envelope. These peaks are caused by the reflectors which are in the vicinity of the Unknown Position Transmitter. In communication systems, these peaks are desirable because they contain additional energy for a receiver to improve signal-to- noise ratio and more readily decode data. Since these additional peaks are caused by reflectors in the vicinity of the UPX, they may also be considered as a "signature" or "fingerprint".
- This additional information may be able to provide cues to an appropriate central processing device.
- Neural networks are especially well suited for such imperfect and complex information.
- a RAKE receiver designed for time of flight usage would supply information from multiple peaks, and perhaps valleys as well, to the central processing unit. This information would associate the amplitude of a peak or valley with its associated time delay from the initially arriving signal. This signature information is particularly useful when previous training sessions have provided historic information in order to compare a present reading against.
- the system of receivers distributed through a particular coverage area must develop time references from which to compare the position of the arrival of a transmission from a UPX. Several techniques to accomplish this antenna grid calibration/synchronization are described herein. For example, a GPS receiver can be outfitted with a real time reference.
- This reference is tightly coupled to the accuracy of the cesium atomic clocks used by the GPS satellite system.
- the output of such a receiver can produce one second time ticks such that every system receiver outfitted with a GPS receiver would simultaneously receive a "beginning of one second interval" time marker as well as a high frequency accurate clock output period.
- Any further time offsets from GPS receiver to GPS receiver may be caused by the varying distances between that receiver and other associated receivers. These can be corrected through either an initial fixed offset or by differential GPS techniques which are well known in the art.
- one or more master references may be installed which can provide evenly distributed time markers which can then in turn calibrate the internal time base of the receivers located in a coverage area.
- the synchronizing transmitter may be one single transmitter located at an elevation appropriate to be received by all receivers of the coverage area.
- multiple synchronizing transmitters may be placed at lower elevations and distributed throughout a coverage area such that all receivers are within radio view of a synchronizing transmitter.
- the fixed position reference transmitters, FRX's may be distributed throughout a coverage area such that every receiver is capable of receiving a reference message from one or more of the FRX's. These. FRX's do not recalibrate the internal time base of the receiver, rather they provide a relative time stamp from which to measure subsequent UPX transmissions.
- This compensation means may be implemented as a pre-processor or pre-neural network to the position determining neural network.
- the pre-neural network may employ a constant retraining method using the fixed references as known. This would reduce the complexitv of the subsequent position determining neural network processor.
- some or all of the receivers in a coverage area may be equipped with an associated transmitter. This transmitter transmits at a fixed interval based on the receiver's interval time base. This information may be further used to compensate for the drift of the receiver's internal time base. Additionally, during these specially transmitted messages, the receiver's internal reference counter may be transmitted as part of these periodic messages.
- This provides additional information to compensate out drift errors due to the receiver's internal time base.
- This compensation can be accomplished either algebraically or via neural network means as described herein.
- An additional benefit of such techniques is that changes in overall system propagation path and propagation speed variations will be automatically compensated for as the system compensates for the drift resulting from receiver time base imperfections.
- Neural networks may further be able to compensate the drift on a third order or greater basis and may even take into consideration variations associated with time of day or time of season on a receiver's time base and the system as a whole. This would have the effect of allowing the use of lower cost time references and possibly even uncompensated crystals.
- a receiver may measure its operating temperature and send that information to the central processing device in order to enhance such temperature drift corrections.
- the fixed reference transmitters can be used by the central processing unit to correct drift on a higher level basis. Since the central processing unit will know that the fixed reference transmitters do not move, it may also adaptively correct all of the readings from fixed reference transmitters such that the latitude, longitude, altitude position fixes remain constant at their known points of origin. In order for the central processing unit to effect such constant positions of the fixed reference transmitters, even in the face of receiver time base drift, correction factors must be provided either methodically or by altering the weights on a neural network's synopsis. The neural network system will automatically make these system-wide corrections. The same corrections may be applied to the reception from UPX devices. These system-wide corrections will automatically correct for errors which might have been caused by either seasonal, propagation path, propagation speed, or time base drift and yield more accurate position fixes for UPX devices.
- Figure 1 is a system diagram of the entire system showing the receivers, with optional directional antennas and transmitters, receiving radio signals into a central processing device (CPD) from an unknown position transmitter (UPX) and, optionally from a mobile reference transmitter, a fixed reference transmitter, and a grid synchronizing transmitter;
- Figure 2 is a schematic illustration showing the shortest path and a reflection of a transmitted radio signal from a UPX off of a fixed object;
- Figure 3 is a schematic illustration showing a reflection of a transmitted radio signal from a UPX off of a temporary obstacle;
- Figure 4 is a schematic illustration showing a training transmitter and a UPX broadcasting training signals from multiple locations to train the network in the CPD;
- Figure 5 is a schematic illustration showing a neural network with reference time and position cue inputs and latitude, longitude, altitude and accuracy outputs;
- Figure 6 is
- FIG. 1 shows a system overview of the present invention.
- the central processing device 100 collects information from several receiving sites 102.
- the central processing device 100 uses historic information and other cues in order to enhance the accuracy of a position fix calculation.
- the output of the central processing device 100 is essentially X, Y and z, and more particularly latitude, longitude, altitude and, optionally, accuracy of position fix conversions, velocity of a UPX or heading of a UPX.
- the central processing device may derive improvements from a table or matrix of correction coefficients.
- the central processing device may also be a neural network device whereby previous history is represented as weighing on the neural, network's synapses.
- the central processing device also benefits from other information and cues 101 such as time of day, time of season, humidity, known location of receivers, GPS data, temperature, previous determination of velocity in vector, and direction vectors.
- the receivers 102 are synchronized by a grid synchronization transmitter 106, GPS satellites, or the like.
- the purpose of the overall grid synchronization is to provide a consistent and accurate reference by which to compare arriving signals from other system elements.
- the purpose of the radio location system as taught herein is to accurately determine the location of an Unknown Position Transmitter, UPX, 103.
- the UPX may be a transmit-only device, in which case transmissions are either periodic, based on some internal time reference and/or transmissions, or via initiation by some outside stimulus, including a request for help.
- the UPX may also be a two-way communication device whereby a transmission is initiated also upon the reception of a polling signal. Lastly, the UPX may be implemented as a transponder whereby round trip Time-of-Arrival measurements may be provided.
- the Unknown Position Transmitter would typically include in its transmitted message an identification code as well as other data. This data may include the city of origin code, status information such as battery low, device OK, a modulo transmission number counter, or a supplier code in order to logically isolate systems which may be provided by two independent suppliers/manufacturers. The data may further contain an indication of the time of the next transmission. This message would typically be forwarded by a third detection/error correction code to enhance the reliability of the received message.
- the status of reference fields would be supplied to indicate medical emergency, roadway assistance, police emergency, kidnapping, tamper, etc.
- the dispatch operator at the central station may further guide a search team equipped with a mobile reference transmitter, MRX 105, in close proximity of the UPX 103.
- MRX 105 mobile reference transmitter
- the central processing device may thereby accurately compute the differential vector which represents the path and direction which a search team must travel in order to intersect the UPX 103.
- the MRX may also be provided with a transponder mode to repeat the UPX transmission. This repeated transmission has an added path delay compared to the MRX. This added delay forms a radius about the MRX. The resulting sphere may be used by the central monitoring station to augment the position calculation of the UPX.
- the system may further benefit by one or more fixed reference transmitters, FRX's, 104. The purpose of the fixed reference transmitters is to provide transmissions from known fixed positions within a particular coverage area. These fixed reference transmitters are used by the central processing device 100 order to calibrate system errors due to varying environmental conditions as well as drift caused by imperfect time bases within the various receivers.
- a receiver 102 may provide to the central processing device 100 information which includes Time-of-Arrival, TOA/Relative Time-of-Arrival, RTOA, signal-to-noise ratio, SNR and antenna quadrants (A,B,C,D) 108.
- the receivers 102 may optionally be equipped with multiple antennas separated into four or eight quadrants 107. If each antenna is provided with its own independent receiver, each receiver may provide different and useful Time-of-Arrival information. Alternatively, an antenna may be selected which yields the strongest signal. As a further alternative the antenna may be selected which provides the earliest arriving signal.
- Cellular telephone systems for example, provide both signal- to-noise ratio information as well as antenna quadrant information.
- the transmitter may, as a part of its data message, include bits which indicate the time duration until the next transmission by that UPX.
- the UPX may transmit on regular or on a known transmission interval pattern. Even is a pseudo-random pattern was used by the transmitter, a receiver knowing that pattern would be able to take or more readings from the UPX, and from the time separation, predict the next occurrence of a UPX transmission.
- each tower must be surveyed for precise latitude, longitude, altitude positions.
- the fixed reference transmitters, 104 may function to serve this purpose.
- the fixed reference transmitters would themselves have to be accurately site surveyed for latitude, longitude and altitude, however. Since the absolute position of the fixed reference transmitters 104 would be known, the central processing device 100 would be able to adjust the resulting position fixes to coincide with the true position of the fixed reference transmitters. Providing the fixed reference transmitters 104 are adequately distributed through a large area of interest, the system would be able to automatically self-calibrate its position fix references. This feature may be useful for quick deployment or temporary deployment systems where the added step of site surveying every receiver may be too time consuming.
- GPS interface to these devices would remove the need for a survey and allow for rapid deployment to help search teams or provide temporary coverage.
- some errors will be consistent due to the overall geometry and position of fixed obstacles in a certain area.
- UPX 103 transmits a signal to Receiver 102
- its direct point-to-point path 203 is blocked by fixed obstacle 201.
- the first arriving signal is equal to the distance between the UPX 103 and the Receiver 102, it is instead equal to that true distance plus a relatively repeatable Time-of-Arrival error 206.
- This Time- of-Arrival error 206 is equal to the effective path increase taken by the signal in order to be received by Receiver 102.
- This Time-of-Arrival error 206 may be estimated as a guess by swinging two arcs.
- One arc 207 would begin at the UPX 103 with the radius center at the receiving antenna 102.
- the other arc 208 would begin at UPX 103 with radius point of origin of 209. This would effectively swing dashed line 204, into the position of dashed line 205.
- the difference in position of the two arcs, 207 minus 208, would equal the Time- of-Arrival error 206.
- This fixed error could be learned and stored in a correction factor table, a correction factor matrix or in the weightings of synapses in a neural network.
- errors in position fix accuracy may also be caused by temporary obstacles such as moving automobiles, buses, trains, etc.
- the direct path of transmission from UPX 103 to receiver 102 is blocked by a bus noted as 301. Instead of the signal from the UPX 103 arriving directly, it's first leg of travel 305 is reflected off of bus 301. The reflection 306 then bounces off of building 304 to finally travel a path 307 to receiver 102.
- These added reflections again add an error term which is in excess of the direct theoretical point-to-point path traveled.
- Several tactics may be employed to eliminate the errors due to temporary obstacles.
- One such tactic is to deploy a number of receiving towers which is greater than that required to provide the position fixes desired.
- a receiver, or receivers, suspect of error due to additional path travel artificially created by a blocking obstacle may be eliminated from a calculation or may be lowered in weighing by a neural network.
- short term diversity may be used such that subsequent transmissions from a UPX may no longer be blocked by a particular temporary obstacle.
- rule based methods may be utilized to intelligently reduce the effective travel path measurement in a manner to increase the position fix accuracy.
- a training session depicted in Figure 4
- This training may also proceed over the normal operation of the system's lifetime.
- the purpose of the training is to associate transmissions from a UPX with independently derived position information which accurately indicates the actual position of the UPX.
- a mobile team or a training vehicle 400 would be equipped with a training transmitter 401.
- the team or the vehicle would then traverse the coverage area of interest.
- the mobile team or vehicle would particularly concentrate in areas of high multi-path reflectors such as multi-story buildings 403.
- reference transmissions are made.
- "X"s indicate the locations of reference transmissions. Each transmission would also coincide with an indication of actual location of the vehicle.
- the training transmitter 401 consists of several blocks.
- a transmitter radio beacon 406 which is either an Unknown Position Transmitter, UPX 103, or a MRX 105, where the transmitter radio beacon is capable of being located by remote receivers.
- the vehicle would house some absolute reference position determining means 408. Such means may include one or more of the following: "map matching", GPS, dead reckoning, calibrated odometer, user call-in, etc. This absolute reference would typically be connected to a data transmitter 407. Alternately, a voice link may be used for an operator to call in absolute reference information.
- the radio beacon 406 can transmit absolute reference position information directly.
- a user may call in their position and simultaneously enable a transmission from a UPX 103. This is particularly useful in situations where increased accuracy is desired. This can often be in places where a user typically frequents, such as the home or an office in a multi-story building 403. As shown in figure 5, several approaches may be taken to accomplish the enhanced position calculations as described herein.
- the preferred embodiment of the instant invention uses a neural network approach. A typical neural node is shown in inset 517. Each neuron has one or more inputs 506 which are summed into a node 508. The resultant sum is output at 509. Each input is assigned a weighing factor 507.
- the weighing factor may be positive or negative, and may be accomplished with actual resistors and summed to additive or subtractive nodes of an amplifier. Alternatively, these "resistors" may be coefficients stored in a matrix. The coefficients may have as much resolution as is defined by the number of bits provided.
- Neural network software is available which can run on conventional Von Newman processors. There is also dedicated parallel processing hardware available which performs calculations in digital form. Lastly, fully analog integrated circuits are being developed which contain hundreds or thousands of individual nodes. A neural network is able to accomplish its function after one or more training sessions. The training sessions adapt the weighing factor magnitude and sign until the output or outputs yield some desired response. A number of training methods exist and are noted herein. It is anticipated that further training methods will become available.
- the neural network in the preferred embodiment consists or input layer 500, a hidden layer 502 and an output layer 504.
- the input layer 500 is connected to the hidden layer via multiple associations such as 501.
- the hidden layer 502 is associated with the output layer through multiple associations such as 503.
- the output of the neural network provides latitude, longitude, altitude and optionally EMS accuracy estimates, 505.
- Time-of-Arrival information relative to a GPS absolute reference located at each receiver 513 may be provided as an input to the neural network.
- time differences, TD's may be computed prior to providing this information to the input layer of the neural network.
- the TD can be computed as a Relative Time-of-Arrival from receiver N minus Relative Time-of-Arrival from receiver N + M.
- Relative Time-of-Arrival information from a receiver "X" 515 may be directly provided to the input layer 500 of the neural network.
- the information provided from each receiver may include one or more of the following: TOA/RTOA, correlation function leading edge slope SNR, ANT (A,B,C,D) and/or multiple RTOA/TOAs from rake type receiver, and/or carrier phase, modulation phase, data position.
- Other system cues 516 may be provided to the neural network's input layer 500. Such system cues may include a real time clock, possibly in sub-second increments. A time of day/time of year clock, barometric pressure, atmospheric humidity, or any other parametric which may effect the Time- of-Arrival of a radio wave from a UPX 103. Most applications would be such that the UPX sends multiple transmissions. These multiple transmissions will benefit by temporal diversity.
- the neural network may take advantage of this additional temporal information by feeding back 510 latitude, longitude, altitude and EMS accuracy estimation information to the neural network's input layer 500.
- a first in, first out, FIFO, 511 may be used to buffer "N" readings from a particular UPX.
- signal averaging may be employed and reduce multi-path errors which are Gaussian or noise like in nature. It is known in the art that transmissions from moving vehicles tend to have multi-path errors which average out. Further, these past "N" readings may be used develop trend information such as velocity and direction vectors.
- the associative memory like the neural net, also require an initial and/or ongoing training process.
- the associative memory may also be equipped with similar inputs as described herein as well as the same outputs.
- the inputs to the neural network may also include multiple peak/valley information from a RAKE type receiver. This information would be in the form of amplitude versus time delay from some reference point. A desirable reference point would be that of the first arriving signal of the delay spread profile.
- carrier phase, data bit position- or data modulation phase information may also be provided to the inputs of the neural network. This information may be particularly useful for cellular radio telephone type systems where chip code position and direct sequence information is not available. This phase information in combination with the Signal-to-Noise Ratio and antenna quadrant information are all available or can be derived from a cellular receiving node. This information, when enhanced by the neural network, or by the other processor means as described herein, will provide increased accuracy position fixes. For non-cellular telephone type systems, this carrier phase, data bit position, data modulation and phase information may be used in combination with other cues such as time of flight information from a direct sequence system. Figure 6 shows a correction factor matrix used to enhance an estimation of the location from which an Unknown Position Transmitter transmitted.
- correction matrix 600 maps into the latitude 601 and a longitude 602 of the coverage area of interest.
- the resolution of the grid pattern must be great enough to isolate anomalies due to multi-path reflectors which tend to cause repeatable errors.
- Each storage node of the correction matrix may contain gross latitude, longitude and altitude correction factors or may contain finer correction factors to Time-of- Arrival/Relative Time-of-Arrival readings from one or more receivers prone to repeatable half errors due to fixed obstructions.
- a conventional method produces an initial uncorrected position fix.
- This initial position fix is used to perform a table look-up from the correction matrix.
- the correction factor or correction factors are then applied to the previous Time-of-Arrival/Relative Time-of-Arrival prior to recomputation.
- the correction factor may contain gross corrections of latitude, longitude, and altitude which can then be directly applied to the first position fix calculation.
- interpolation means may be applied in order to further enhance the accuracy of the correction.
- a system of simultaneous equations or differential equations may be employed.
- FIG. 8 is a flowchart which illustrates a method of reducing the effects of multi-path error without using tables or matrices.
- the method takes advantage of the fact that a multi-path delay may only effect a single receiver.
- a receiver's Relative Time-of-Arrival is used to compute a time difference, then every time difference will have a consistent multi-path error from a particular receiver.
- the following algorithm takes advantage of these two rules and may be applied independently or in conjunction with the three previously noted processing techniques in Figures 5, 6 and 7.
- a computation is made of a position fix 800 if the convergence error 801 is acceptable, then the error reduction algorithm is not invoked. If the convergence error is unacceptable, then the algorithm proceeds to step 802.
- Step 802 incrementally reduces the Time-of-Arrival or Relative Time-of-Arrival of receiver "N". The position fix is then recomputed.
- Block 803 determines if the convergence error improved over the previous position fix. If it did, control is looped back to Step 801, if it did not, control is passed to Step 804. Since the convergence error did not improve, the fast Time-of-Arrival or Relative Time-of-Arrival of receiver "N" is restored because it yielded a better position fix.
- the next step 805 selects the next available receiver in a particular coverage area. The receivers would likely be limited to those in close proximity to the UPX of interest thereby reducing the number of iterations required in the algorithm.
- the algorithm uses decision block 806 to loop back to step 802 until all of the receivers have been sought for improvement.
- the algorithm may still provide some improvement even though it is not the level of improvement desired.
- the reading from that receiver may be eliminated from subsequent position computations.
- Relative Time-of-Arrival or time difference measurements suspected of large errors may be shunted from the position calculations. This tactic may be used with any of the computation techniques as taught herein.
- Figure 9 shows that additional complexities are encountered when trying to locate a UPX 103 in a multi-story building 901. The walls in construction of a building greatly attenuate the signal path before the transmitted signal reaches a window, door exit or vent.
- the transmitted signal Since the transmitted signal must follow a common path 904, once the signal exits the building, it will appear to be a point source when received by the time of flight system's receivers 102. If the signal is strong enough to exit via more than one window or doorway then multiple point sources will be apparent to the radio location receivers 102. This will force a delay spread profile with leading edge peaks and valleys caused by the constructive and destructive cancellations of the signals leaving multiple exits in the building 901. RAKE receiver techniques as disclosed herein may take advantage of this enriched information in order to better predict the position of a UPX 103 which is located within a single story or multi-story building.
- the user of a UPX frequents a particular building, they would be able to invoke a special training session by calling into the central station operator and forcing the UPX 103 into a burst of training transmissions.
- the central processing unit would be able to store the resulting signature and use it at a later time to better predict the location of a UPX within that building.
- the first arriving information yields the highest degree of accuracy in a time of flight radio position determination system.
- subsequent information may also be useful.
- One such situation is attempting to locate a transmitter within a building. Several leading edge peaks and valleys may result in the received signal due to different signal propagation paths.
- This delay spread profile 1000 may provide cues to determine exit points from a building as previously discussed in Figure 9.
- the other later arriving peaks and valleys are caused from reflectors which are in the proximity of the UPX.
- These additional peaks 1003 and valleys 1005 may be utilized to enrich the input to a neural network processing means.
- the typical delay spread is indicated by Figure 10, where the amplitude is shown in 1002 and increasing time increments in 1001. Time equals zero is noted by 1004 and is synthetically set by the first arriving signal which is detected.
- This profile may be learned by a neural network by invoking a training session for that purpose.
- RAKE receiver devices were developed for radio data communications so that signal energy from multiple peaks could be collected and exploited to increase a signal's effective Signal-to-Noise Ratio. This benefit would also be enjoyed by a radio location system which utilized a RAKE type receiver since more transmitted signal energy is being effectively used by the receiver to make a time of flight measurement.
- Neural networks are particularly well suited to accept information from such a receiver output. The receiver would output information from several peaks and/or valleys which would include amplitude, phase information, as well as distance from Relative Time equals zero. The peak and valley information associated with the leading edge of a delay spread profile may be further employed to enhance the effectiveness of the use of a mobile reference transmitter.
- the leading edge signature of the delay spread profile will become more and more similar to that of the UPX.
- the network will be able to establish a prediction to at least advise the mobile reference team if they are growing closer to the UPX or further away.
- the neural network may also be able to provide enhanced accuracy differential position vectors with the added input of the peak and valley information from the leading edge of a delay spread profile. Grid synchronization of the receivers utilized within a desired coverage area must be accurately and reliably provided. Any uncorrected errors due to time base drift will cause systematic errors in position fix accuracy.
- FIG 11 depicts a Relative Time-of-Arrival receiver utilizing a GPS receiver as a reference period.
- GPS satellites are outfitted with highly accurate Cesium atomic clocks as references. That reference information can be derived by a land based GPS receiver.
- the GPS receiver uses an internal time reference which is recalibrated by GPS satellite transmissions. The time bases free run in between occurrences of GPS satellite lock. Some of these receivers use second order correction techniques to maintain a highly stable internal reference.
- a GPS receiver can be outfitted with a one second tick or a periodic output pulse. This output pulse can be used for system synchronization, whereby the one second tick output of the GPS receiver becomes the reference.
- FIG. 11 shows a counter 1100 being clocked 1104 by a GPS reference or the like 1101
- the GPS reference or the like 1101 also provides a one second or a periodic reset pulse 1105, which is time synchronous to all receivers in a coverage area of interest,
- latch 1102 captures the instantaneous value in the counter 1100
- the latch contents will therefore equal the Relative Time-of-Ar ⁇ val plus time base drift times
- the resulting count in the counter 1200 equals the Relative Time-of-Arrival of the UPX as compared to the periodic synchronization reference plus the time base 1201 drift times the time between receipt of the reference signal 1207 and the signal from the UPX 103.
- this Relative Time-of-Arrival can then be used as an input to a trained neural network that corrects for the clock drift between the signal from the UPX 103 and the time reference 1201.
- the neural network then outputs either a modified Relative Time-of-Arrival that has been compensated for clock drift or an estimate of a location from which an Unknown Position Transmitter transmitted.
- FIG. 13 show that it is possible to achieve grid synchronization without the need for rapid periodic synchronization reference transmissions such as noted in 1207. This requires a modulo counter 1300 with additional counting states to hold larger modulo numbers representing greater time gaps between transmissions, It is also necessary to either have a more accurate time base 1301 or higher-order time based drift correction at the central processing device. Neural networks are well suited to this drift correction as they are able to take into account high order drift correction factors as well as take into consideration nonlinear effects on a receiver's time base 1301.
- the timing indicators are used as inputs to a neural network, and the neural network outputs a drift corrected timing indicator. Such drift corrections may alternately be accomplished, and the corrected values used, in any of the position determination processing methods as described herein.
- the modulo counter 1300 counts clock pulses 1304 from time base 1301. When either a first arriving signal 1303 is detected from a UPX 103 or from a fixed reference transmitter 1308, a clock pulse is generated to latch 1302. Latch 1302 then stores the instantaneous state of modulo counter 1300.
- the FRX 1308 may be co-located or made a portion of receivers which are distributed through coverage area of interest.
- the latch 1302 now contains a number equal to the Relative Time-of-Arrival (since the modulo counter first started) plus a random number (which was present at the modulo counter's startup) plus a drift factor times the time offset from the last FRX reception.
- a beacon transmitter or a FRX is co-located with a receiver, it may embodied as beacon transmitter 1306.
- This beacon transmitter may further be initiated once per a predetermined number of counts via control line 1303 as driven from modulo counter 1300. This has the advantage of using the same transmission interval timer as the modulo counter 1300 which is used for Relative Time-of-Arrival information. In this manner the drift error of time base 1301 is common to both received signals and transmitted beacon signals.
- beacon transmitter 1306 may transmit the content of the modulo counter 1300 upon the receiver detecting a specially coded poll transmission. Beacon transmitter 1306 may further transmit the reception of a transmission from another fixed reference transmitter 1308 which may be co-located with a remote receiver. In this manner, round trip measurement and other synchronizing techniques may be employed. This allows further tactics to eliminate the random number portion which is inherent in the modulo counter. Several other drift elimination tactics can then be utilized by the central processor device.
- the combinational drift factor of RCV1-RCV2 will remain relatively constant over short time durations.
- This combinational reference transmission drift correction factor may then be applied to the same receiver pair when determining the TD of a UPX.
- RTOA, RTOA- - xmit interval
- RND # FRX xmit
- Reading - RTOA This drift factor can be used to correct for resulting position fix errors.
- a system of simultaneous equations may also be employed to resolve drift and to establish receiver synchronization.
- Figure 14 shows two hyperbolic lines between two receivers corresponding to time difference paths.
- the time of flight system may provide either a Time-of-Arrival from a transponder or a Relative Time-of-Arrival from a transmit-only UPX.
- the Relative Time-of-Arrival reading from receiver 2 1403 can be subtracted from the Relative Time-of-Arrival of receiver 1 1402 to yield a time difference or TD. That TD may actually fall on any point of a curved line which follows a hyperbolic pattern.
- This curved line is called a hyperbolic line of position.
- the line of position forms a perfect hyperbola about receiver 1 1402.
- time difference measurements at any individual point along this hyperbolic curve will be subjected to added path of travel.
- All of the processor techniques described herein effectively create a corrected line of position 1401 whereby previous actuarial/historic information is used to derive a correction factor which is applied to readings during the normal operation of the system. This further requires that the error term is computationally resolved to a single receiver. If the error term is reduced to a receiver pair, then the correction factor will appear as 1404.
- any equivalent lockup table or associative memory means may be employed to read a currently measured TD and use that to establish the corrected line of position 1401. The data from the corrected line of position can then be used by position calculation algorithms as are known in the art.
Abstract
Description
Claims
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AU61531/96A AU718991B2 (en) | 1995-06-07 | 1996-06-06 | Enhanced position calculation |
EP96919105A EP0832440A4 (en) | 1995-06-07 | 1996-06-06 | Enhanced position calculation |
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US08/487,522 US5717406A (en) | 1995-06-07 | 1995-06-07 | Enhanced position calculation |
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WO (1) | WO1996042020A2 (en) |
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Also Published As
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AU6153196A (en) | 1997-01-09 |
US5917449A (en) | 1999-06-29 |
US5717406A (en) | 1998-02-10 |
AU718991B2 (en) | 2000-05-04 |
CA2223537C (en) | 2006-11-07 |
CA2223537A1 (en) | 1996-12-27 |
WO1996042020A3 (en) | 1997-02-06 |
EP0832440A4 (en) | 1999-11-17 |
EP0832440A2 (en) | 1998-04-01 |
US6084547A (en) | 2000-07-04 |
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