JP2013088208A - Road map feedback server for tightly coupled gps and dead-reckoning vehicle navigation - Google Patents

Abstract

PROBLEM TO BE SOLVED: To implement practical road map correction feedback by combining tight coupling of a global positioning system receiver in a vehicle and dead-reckoning through a wireless network server.SOLUTION: Road map feedback is used in a tightly coupled GPS and a dead-reckoning system for collecting data on a wheel speed transducer in a CANbus network of a vehicle in order to calculate a vehicle range and direction. Road segment information provided by a network server provides constraints templated to a current navigation solution to a database so as to derive correctable feedback. The dead-reckoning closes a gap of the navigation solution that occurs when GPS signal transmission is lost in tunnels, parking lots or any other general situations. The adaptation of the roadmap controls drifts accumulated for a long period of dead-reckoning single operation.

Description

  The present invention relates to car navigation systems, and more particularly to roadmap correction feedback provided by a radio network server for a globally coupled positioning system (GPS) receiver and dead reckoning (DR) tightly coupled combination in a vehicle.

  GPS navigation systems with street map displays are now widely available in most new vehicles around the world. New map updates appear to be purchased and installed on DVD discs and published annually on a yearly basis. Typical GPS navigation receivers used in these vehicles are tens of meters accurate in good environments, but can drop to 100 meters in dense urban environments. These car navigation systems assume that the vehicle is traveling on a road on the map and therefore use the map information to snap the vehicle location icon to the exact route of the nearest road, but GPS reception is If lost in the same way in tunnels and parking lots, the user position on the screen of the map display is simply not updated.

  Factory installed navigation systems are generally expected to provide higher reliability and accuracy compared to portable navigation devices in the repair parts market. The driver will not tolerate long start-up times or navigation failures simply due to entering a tunnel or parking lot. Thus, conventional factory-installed navigation systems include inertial sensors such as speedometers, travel recorders, gyros and accelerometers, and vehicle data buses for accessing speed, forward / reverse, and mileage information. It is connected. However, inertial sensors impose higher costs.

  Obtaining arbitrary course information in conventional systems requires that an expensive and delicate directly coupled automotive gyroscope be installed. SiRF Technology, Inc. (San Jose, Calif.) Sells a solution that they claim to eliminate this relatively expensive sensor and instead use sensor data already available from other vehicle subsystems. ing. According to SiRF, sensor data measurements must be accurate enough to extract meaningful information for dead reckoning, and sufficient frequency must be provided for sensor measurements. Also, any delay in sensor data delivery to the dead reckoning system must be short, for example, a latency of 10 milliseconds or less.

  Most new vehicles in North America and Europe are equipped with vehicle speed sensors and anti-lock braking systems (ABS) as standard equipment. Compass is more frequently seen in the United States than in Europe, but stability control is more common in Europe than in the United States. Such dead reckoning software must take into account the various availability of a particular sensor. The early SiRFdrive 1.0 was configured for a vehicle platform with a direct-coupled gyroscope, while the later SiRFdrive 2.0 used distributed ABS module sensor data instead. SiRFdrive 2.0 calculates the individual wheel speed and determines the speed of the vehicle 110 along with its rotational speed, so that expensive gyroscopes can be eliminated. The SiRFdrive 2.0 dead reckoning system is described in the press release as collecting wheel rotation ticks (ie speed pulses) from each wheel. It further determines the calibration value required for accurate dead reckoning. The better the resolution of the wheel increment data (for example, the greater the number of wheel pulses per revolution), the better the overall dead reckoning performance.

  Since the wheel rotation step data is read directly from the vehicle bus, there was no need to connect to the wheel sensor itself. However, using raw ABS data is not so easy. Dead reckoning requires the highest resolution at low speed because the maximum course change usually occurs when turning a road intersection at low speed. The main function of the ABS module is to control the locking of individual wheels that occurs when a strong braking system is applied at high speeds. Thus, some ABS modules do not send measurements at their maximum resolution, and wheel sensor ABS modules may output inaccurate data at low speeds or no data at all. In these cases, the ABS software is usually upgraded to provide the necessary solution and the low speed data output required by dead reckoning applications. The advertising literature says that SiRFdrive 2.0 has sophisticated algorithms and such data loss minimizes the negative effects of having accuracy at low vehicle speeds.

  Unfortunately, such a wheel-driven dead reckoning system does not meet those promises. What is still needed is a practical system with self-calibration and correction algorithms that work in combination with GPS and dead reckoning.

  Briefly, roadmap feedback is used in the tightly coupled GPS and dead reckoning system of the present invention, and in one embodiment, collects wheel speed transducer data on the vehicle's CANbus network and computes vehicle range and direction. To do. The road segment information provided by the network server provides a database of constraints templated to the current navigation solution, so that feedback for correction is derived. Dead reckoning bridges the gap in navigation solutions that occur when GPS signal transmission is lost in tunnels, parking lots, and other common situations. The continuous calibration of wheel radius and compensation for speed effects is computed from the GPS fix, which improves dead reckoning performance and accuracy during long outages of GPS signal reception. The roadmap adjustment controls the drift accumulated by long-run dead reckoning alone. When recovered, the dead reckoning solution provides a high-quality starting point for GPS receivers that search the surroundings.

  The above and further objects, features and advantages of the present invention will become apparent in light of the following detailed description of specific embodiments thereof, particularly when taken in conjunction with the accompanying drawings.

1 is a functional block diagram of an embodiment of a tightly coupled GPS and dead reckoning system of the present invention for a four wheel vehicle with a vehicle bus network. FIG. 2 is a functional block diagram of two possible implementations of the combination of the GPS receiver and dead reckoning (DR) computer of FIG. The GPS, DR, and map matching composite system of the present invention that can be implemented with various hardware and software, such as in FIGS. 2 (a) and (b), for the system application shown in FIG. It is a functional block diagram of an embodiment. FIG. 3 is a stage diagram showing start-up, operation and end stages of operation of a tightly coupled GPS and dead reckoning navigation system as in FIGS. FIG. 3 is a flow chart illustrating the transition between various calibration states of a tightly coupled GPS and dead reckoning system such as FIG. 1, FIG. 2 (a) and (b). FIG. 6 is a flow diagram of a fix mode state machine that controls the interrelationship in dead reckoning single mode, compound mode, and GPS single mode. FIG. 2 is a functional block diagram of a tightly coupled GPS and dead reckoning system for a vehicle as in FIG. 1. It is a graph which shows the speed effect in a wheel radius. It is a time series figure showing the difference of the time tag of two continuous GPS course observations. It is a time series diagram which shows the relationship between the time of a series of position fix, and the time when the feedback with respect to corresponding position fix is returned. FIG. 6 is an associated flowchart showing how feedback is determined to be valid and whether it should be used for DR propagation. FIG. 6 is an associated flowchart showing how feedback is determined to be valid and whether it should be used for DR propagation. FIG. 3 is a functional block diagram of a server-based roadmap feedback system for tightly coupled GPS and dead reckoning vehicle navigation of the present invention.

  FIG. 1 represents a GPS and dead reckoning (DR) combination embodiment of the present invention, referred to herein by a general reference numeral 100. The combination of GPS and dead reckoning 100 provides navigation information on the display 102 to the user. The roadmap disc and player 103 displays the current user position with respect to the local road. The GPS receiver 104 tunes and tracks microwave satellite transmissions through the antenna 106 and is calibrated “delta-heading” and “delta range” computed by a dead reckoning (DR) computer 108. -range) ”information is tightly coupled. The term “delta” represents how the course (ie, direction) of the vehicle 110 has changed over time or how the range (ie, distance) has changed over the same time period.

  Both GPS receiver 104 and roadmap disc and player 103 provide corrections and feedback to DR computer 108. The GPS receiver 104 provides absolute position and course determination, whereas the DR computer 108 can add its calibrated delta course and delta range computation results to arrive at a dead reckoning solution. it can. The roadmap disc and player 103 provides road segment feedback to the dead reckoning solution to prevent small arithmetic errors in the dead reckoning solution from accumulating and drifting from the road segment of the map at long GPS outages. .

  Both the DR computer 108 and the roadmap disc and player 103 are very accurate guesses that will not drift significantly if the GPS receiver has not provided a fix for a significant amount of time and has lost all satellite tracking. Provide navigation solution. In addition, dead reckoning solutions quickly restart the GPS receiver 104 when signal reception is restored when a large increase in position uncertainty is greatly reduced when DR is available for comparison. It is very useful to make it. This envisages worst case movement, where the DR can measure vehicle movement, while a stand-alone GPS receiver promotes its position uncertainty affecting the amount of code and frequency searches. There must be.

  FIGS. 2 (a) and 2 (b) show two methods for implementing the GPS receiver 104 and the DR computer 108. FIG. In FIG. 2 (a), an orbiting navigation satellite transmits a microwave signal that is received by an antenna 202 and is a navigation measurement platform (MP) 204 (eg, eRide with serial output (San Francisco, Calif.)). Demodulated by OPUS-III nanoRide GPS module). The MP 204 is a type in which navigation software is executed on a host processor and includes a 32-channel radio frequency (RF) receiver 206, a baseband 208, and a SAW filtering stage. The MP 204 has a function of a two-channel real-time differential GPS equipped with a geostationary satellite type satellite navigation augmentation system (SBAS). The serial interface 210 can be a USB, RS-232, or similar line-based interface. The host processor 212 executes the user application 214 and has preprocessing capabilities to host client software 216 with GPS, DR, and application programming interface (API) libraries. The function API 218 enables communication of navigation solutions for display to the user, and the CANbus interface 222 receives wheel ticks information from the CANbus 224.

  In FIG. 2 (b), the GPS receiver 104 and the DR computer 108 are implemented with a position, velocity, time (PVT) module 250. For example, eRide (San Francisco, Calif.) EPV3600 can be used. This is a complete GPS / AGPS PVT receiver with an eRide OPUSIII baseband processor with 44,000 valid correctors and an ARM7TDMI-S with on-chip ROM and SRAM Combined with a (registered trademark) -based CPU. It can acquire and track signals down to -161 dBm and can therefore work indoors. The ePV 3600 takes a single low RF input from the ePR3036 GPS-RF front-end chip (equivalent to the RF stage 206 and baseband stage 208). The embedded microcontroller (CPU) 252 operates from an external parallel flash memory, or an on-chip ROM memory or parallel flash memory. The device GPS firmware in library 216 handles acquisition, tracking, and position, velocity, and timing data output. UART 254 and serial bidirectional interface 256 support serial interface protocols that connect to “NMEA” and other applications. The CANbus wheel step 258 is received by another UART 260.

  The NMEA sentence contains a first word called a data type, which defines how the rest of the sentence is interpreted. The GGA statement (Table I) is an example of essential fix data. Other sentences may repeat some of the same information, but also provide new data. Any device that can read the data can screen the data sentence it is interested in. There is no command to control the GPS, it simply transmits all the data it has even if many are ignored. The interceptor computes its own checksum and ignores any data with an incorrect checksum. The NMEA standard defines statements for all types of equipment used in marine applications. All sentences related to GPS receivers begin with “GP”.

The so-called NMEA0183 standard uses a simple ASCII serial communication protocol and defines how data is transmitted in a “sentence” from a single “originator” to multiple “interceptors”. An intermediate expander allows the sender to transmit to almost any number of interceptors, and using a multiplexer, multiple sensors can send to a single computer port. A third-party switch is available that can establish primary and secondary callers by automatic failure bypass if the primary fails. The above standards define the content of each sentence (message) type in the host CPU application layer, so that all interceptors can parse the message correctly.

  In FIG. 1, the vehicle 110 has two front, steerable wheels 112 and 114 and two rear, non-steered wheels 116 and 118. Note that for a given turn, the turning radius of the inner wheel must be much smaller than the turning radius of the outer wheel. For that reason, the calculation is complicated and depends on the steering angle, so it is not practical to derive the course and range information from the front steering wheel.

  An antilock braking system (ABS) transducer 120, 122, 124, and 126 is attached to each wheel in FIG. These transducers, sometimes referred to as wheel speed sensors (WSS), generate electronic pulses (ie, “ticks”) as the wheel turns. Some such transducers use variable reluctance and optical detectors to measure wheel rotation. The variable reluctance WSS often uses a knurled “tone wheel” attached to the wheel rotor to produce a digital electrical output similar to a variable audio tone. If the wheel locks, the digital pulse stops and the ABS controller 128 acts to shut off the hydraulic pressure to the brake caliper of that wheel trying to recover the traction of the four tires on the road.

  ABS sensor information and many other vehicle data in digital packet format are communicated by industry standard CANbus 130. Dead reckoning computer 108 receives ticks of wheel rotation on CANbus 130 from nodes 132, 134, 136, and 138.

  The Controller Area Network (CAN) is a vehicle bus standard that allows microcontrollers and devices to communicate with each other in a host computer or thousands of individual wireless vehicles. The CAN specification was published in 1991 by Robert Bosch (Stuttgart, Germany). See www.can.bosch.com/docu/can2spec.pdf

  Data traffic is multiplexed onto a single dual-wire bus (CANbus 130) and can include engine management, body control, transmission control, active suspension, automatic protection devices, environmental control and security information exchange. CAN is now the standard in OBD-II vehicle diagnostics and is mandated in all vehicles and light trucks manufactured in the US since 1996. The European On-Board Diagnostic Machine (EOBD) standard is similar, and is mandatory for all gasoline vehicles sold in the European Union since 2001 and for all diesel vehicles since 2004.

  A transmitter in the CAN network broadcasts a message to all other nodes in the network. Each message has a unique type identifier so that the node can identify whether the message is appropriate for them. These identifiers further include a message priority field, so that the CAN network can adjust the priority between conflicting messages. A typical CAN implementation uses a twin-wire bus and has a maximum data transfer rate of 1 megabit / second. The CANbus data format has an extended error checking capability built into each data packet. The protocol automatically handles message collisions on the bus, so that higher priority messages can be moved before lower priority messages. Multiple controllers may be located on the same bus, thereby reducing the amount of wiring and the number of connectors in the vehicle 110. This also means that additional modules can be added more easily to conventional vehicle networks, such as dead reckoning computer 108.

  Whenever CANbus 130 is idle, any unit can start sending messages. If multiple units start sending messages at the same time, bus access collisions are resolved by bitwise adjustments using identifiers. The coordination mechanism ensures that no information or time is lost. If a data frame and a remote frame with the same identifier are started simultaneously, the data frame wins the remote frame. During adjustment, all transmitters compare the level of the transmitted bit with the level monitored on the bus. If these levels are equal, the unit can continue to send. If the “inferior” level is sent and the “dominant” level is monitored, the unit has lost its adjustment and must be canceled without sending any more. CANbus 130 provides a single channel to carry bits from which data resynchronization information is derived. The implementation of the channel is not indicated herein, thus allowing a single wire to be grounded, two different wires, optical fibers, etc.

  Information from the wheel tick sensors 124 and 126 for the left and right non-steered wheels is used to derive the basic delta range and delta course of the vehicle 110. Each wheel rotation produces a fixed value of the transducer pulse monitored by the antilock brake system (ABS) 128.

  The arithmetic average of the number of left and right wheel rotation ticks collected by the dead reckoning computer 128 in a given cycle can provide an accurate delta range measurement when the wheel circumference or diameter is known with some accuracy. . The distance information obtained from the GPS receiver 104 over that same period is used for ongoing and continuous self-calibration.

  The difference in the number of rotation steps between the left and right non-steer wheels is likewise proportional to the delta course measurement when the wheel circumference or diameter is known accurately. Any error or change in the circumference or diameter of the wheels 116 and 118 will, of course, cause a corresponding error in the delta course and delta range estimates. Wheels, especially those tires, can change their diameter significantly with speed, tire pressure, temperature, wear, load, certain failures, and after-service operations.

  While a substantial step error in the delta heading and delta range estimates may occur as the vehicle 110 moves, dead reckoning computer 108 or CANbus 130 may cause the vehicle 110 to move without moving the engine. When it is stopped. Such type of error can occur when the entire vehicle 110 is transported by trailer or ferry.

  Prior systems did not manage or control errors in the delta heading and delta range estimates very well. Embodiments of the present invention are distinguished in these respects from the prior art by the techniques described below.

  Dead reckoning computer 108 automatically integrates the delta range and delta heading measurements. It receives from the start position and course to the dead reckoning estimate expressed in packets of local level (north, east) coordinates. The initial delta range and delta heading conditions are obtained from position and velocity data routinely provided by the GPS receiver 104.

  FIG. 3 shows a combined GPS, DR, and map matching system 300 that can be implemented as in FIGS. 2 (a) and 2 (b) for the application shown in FIG. The system 300 includes a GPS receiver 302 that produces a GPS fix 304 that depends on outage and elapsed time if the antenna 306 is unable to receive microwave transmissions from a number of orbiting GPS satellites 308. ing. Dead reckoning propagation processor 310 receives wheel ticks 312 from the wheels of the vehicle that are proportional to the number of left and right rotations, respectively. The mode selector 314 selects whether to output the GPS alone, the DR alone, or the GPS and DR navigation solution in the composite solution 316. The roadmap disc and player 318 provides road graphics to the user location display 320 and road segment information to the device 322.

  Conventional practice is to visually “snap” the displayed user position to the nearest point on the road, even if the GPS position solution is not there. Here, the feedback time and position (TP) structure 324 provides information for “snapping” the combined GPS and DR navigation solution 316 to the nearest appropriate point on the matching road route. Each time the snap error exceeds a predetermined value, the GPS and dead reckoning mixed position is corrected for drift from the position shown on the map. The threshold is necessary to allow for small temporary detours and detours not provided by the map.

  Without such feedback, GPS and dead reckoning mixing errors may continue to increase beyond the map matching algorithm's ability to snap to the road. A typical example is the case of traveling in a long tunnel that is parallel or intersects with the ground surface. If map matching is accurate before entering the tunnel, the feedback will not cause any dead reckoning error to exceed a predetermined threshold. The map matching algorithm may otherwise indicate an out-of-road condition and accidentally snap to a parallel or surface road. Feedback makes map matching work even with large dead reckoning calibration errors.

  One advantage of server-based feedback is that it can provide a highly accurate location solution to the user and does not require the inclusion of a map matching algorithm. Without map matching, dead reckoning errors can accumulate and result in endless position errors. However, if the cost including the map matching algorithm results in nothing, the user will later suffer from poor position accuracy. One advantage of the present invention is that the cost of map matching can be integrated into the server and distributed to many subscribers. The GPS receiver itself provides map matching, and more importantly, allows the user to display the location solution directly on a lower cost map unit where feedback does not need to have an implemented map matching algorithm. Enable. Therefore, manufacturers and users can avoid the cost of license and map matching algorithm development.

  The normal TP structure 326 is used when a good GPS solution is available to reset the GPS and DR navigation combined solution 316 to a GPS solution. The DR calibration 328 includes an initial on-going calibration of the wheel radius estimates and individual wheel radius differences that occur over turning, speed, and linear driving. Dead reckoning propagation processor 310 uses these calibrations to compute ranges and headings from wheel ticks 312 reflected and calibrated from spare GPS positioners 304.

  When a long time elapses in the GPS positioning device 304, the GPS navigation receiver 302 must normally perform a wide search to acquire the GPS satellite 308 again. Here, however, the DR range and course propagation processor 310 spends much of the GPS outage on continuing the calculation of the position solution with the help of mapping feedback 324. Accordingly, these estimated time and position solutions are included in the instruction 330 to the GPS navigation receiver 302 to initiate the initial setting of the current DR solution search. The advantage of instruction 330 is that it can generally be used to speed up recapture and can perform a more sensitive search that is more practical in high speed moving vehicle applications.

  Accordingly, the GPS receiver 302 is configured to search for parallel and independent assumptions using a number of available valid correctors (44,000 or more). Some of the valid compensators in the GPS receiver 302 search for dead reckoning solutions in a very tightly coupled manner so that if the dead reckoning data is correct, the reacquisition time is minimized. If dead reckoning data is of low reliability, it can search for alternative assumptions simultaneously. In the latter case, the GPS receiver 302 recovers quickly after a long outage in dead reckoning single mode 314 or after a long power off period, eg, to correct a long unmanaged route on a ferry boat. Used to help do.

For a fix (1 Hz) dead reckoning once per second, 10 Hz wheel rotation step observations are synchronized to the same 1 second fix interval as the GPS fix produced by the GPS receiver 104 or 302. Such synchronization maintains a fixed period between fixes when the selector 314 switches between dead reckoning alone, GPS alone, and combined mode operations. The delta range and delta course based on wheel rotation increments are measured every 1 second GPS epoch. The absolute course is obtained by integrating the delta course with the initial course reference.
dead-reckoning-heading = heading-offset + sum (delta-heading)
Thereafter, any change in the east and north directions can be determined by the following equation:
Delta-East = delta-range * sin (dead-reckoning heading);
Delta-North = delta-range * cos (dead-reckoning heading)
Finally,
East position = initial east position + Sum (Delta-East);
North position = initial north position + Sum (delta-North)
It is. Dead reckoning measurement and calibration parameters are as follows.
delta-range = B _L * C _L + B _R * C _R ;
delta-heading = A _L * C _L -A _R * C _R ;
Heading = Heading-offset + sum delta-heading
here,
C _L , C _R : The number of ticks accumulated in the CANbus packet for each of the left and right wheels over a specified period such as 1000 milliseconds. The wheel rotation increment is generated by distinguishing the current and previous CANbus packets because the CANbus packet content is the accumulated number.
_{B L,} B _R: calibration parameters for delta-range / tick of the left and right wheels (unit: mm / tick).
A _L , A _R : Calibration parameters for delta-heading / tick difference between left and right wheels (unit: minutes / tick = angle * 60 / tick).
Heading-offset: A calibration parameter that translates sum delta-heading to a known course reference.
Thus, valid calibrations are B _L , _BR (simply remapped as “B” and dB), A _L , A _R (ie, simply “A” and dA), and heading offset (heading -offset) estimate is required. The GPS receiver 104 or 302 can accurately measure delta-range, delta-heading, and absolute course, even when reception of the satellite transmission is not blocked. Since a value can be provided, it is used as a reference source for calibration data.

The calibration parameters are initialized from a known relationship of physical attributes (eg, physical parameters) of the vehicle 110. These physical parameters are, here, the left and right wheel radii (R ₁ , R _r : Wheel Radius), the track width distance between the wheels (TW: Track Width), and the number of counts or increments per revolution (CPR). ).

In the rotation of the vehicle 110, the distance along the turning trajectory is the product of the turning radius and the angular change (eg, changed course in radians). The turn radius is related to the road size and is unknown.
delta-range = turn radius * delta-Heading;
(Unit: meters and radians)
The generated wheel rotation increment is proportional to the product of the distance traveled and the number of steps per meter.
Count = delta-range * CPR (ticks / rotation) / [2PI wheel radius];
(Unit: tick and meter)
Therefore,
(Count / CPR) * 2PI * wheel radius = turn radius * delta-Heading
It is.

In turning to the left, for example, the turning radius of the right wheel is equal to [turning radius of the left wheel + track width]. Thus, taking the difference between the left and right delta range formulas erases the turning radius and leaves the next one.
C _L / CPR * 2 * PI * R _l -C _R / CPR * 2 * R _r = TW * delta-Heading
When rearranged, the course change in angle (delta-heading) is as follows.
delta-heading = R _l / CPR / TW * 360 * C _L -R _r / CPR / TW * 360 * C _R
The inspection is as follows.
A _L = R _l / CPR / TW * 360 (degree / tick);
A _R = R _r / CPR / TW * 360 (degree / tick)
Numerical accuracy may be improved by estimating the parameter in units of minutes (eg, angle * 60). Therefore, A _L and A _R are calculated as follows.
A _L = R _l / CPR / TW * 360 * 60 (minutes / tick);
A _R = R _r / CPR / TW * 360 * 60 (minutes / tick)
Here, the rotation increments of the left and right wheels represent a course change, and the average rotation increment of the left and right wheels represents a delta range at the center of the vehicle 110.
delta-range = R1 / CPR * PI * C _L + R _r / CPR * PI * C _R
When inspected
B _L = R _l / CPR * PI (meters / tick);
B _R = R _r / CPR * PI (meters / tick)
It is. Estimating this factor in millimeters improves the numerical accuracy. Therefore, B _L and _BR are calculated as follows.
B _L = R _l / CPR * PI * 1000 (millimeters / tick);
B _R = R _r / CPR * PI * 1000 (millimeters / tick)

Table II shows the physical parameters of a typical vehicle 110 with 17 inch wheel radius, 84 inch track width, and 200 increments per wheel revolution and their corresponding calibration parameters. . The example in Table II represents a realistic situation where one wheel (left) is slightly larger than the other wheel (right). The calibration parameter is a unit shown below.

  After calibration and physical parameters are obtained, an additional parameter (referred to herein as “heading-offset”) is actually needed to initiate dead reckoning. The course offset parameter can simply be determined in real time when sufficient movement of the GPS antenna 106 produces data that can be used for calibration.

The GPS course is calculated from a GPS speed vector as atan (east speed / north speed) every second, and true north is 0 ° and true south is 180 °. Delta course from dead reckoning, every second, is measured from the difference between the wheel rotational increments that are scaled by the parameters A _L and A _R. Total dead-reckoning-delta-heading-sum is the sum of all dead-reckoning delta-headings. The profile of this parameter agrees with the change in the true course, but deviates from the true course by the integration constant. Dead reckoning course is the sum of the total dead reckoning delta course and the final parameter called course offset.

  The course offset is any difference between the GPS course and the total dead reckoning delta course. The course offset can be expected to be a fixed value, but in practice it drifts depending on the stability and accuracy / availability of the CANbus data and the calibration accuracy. Any lost CANbus packets during or between fix sessions can result in unestimable errors in the course offset. The uniqueness of each manufacturer's wheel tick sensor can also affect the stability of the course offset.

  Whenever the GPS speed exceeds zero, the GPS receiver 104 or 302 continues to update the heading offset estimate. In this way, the system 100 can quickly recover from any abnormal wheel tick conditions.

  Both the heading offset and the sum of all dead reckoning delta courses must be kept in pairs in non-volatile memory, so that dead reckoning is available immediately after power on. For example, in “parking mode”, the data pair is fetched at the start of a GPS dead reckoning session. See FIG. This suggests that the data pair must be properly saved at the end of every session using a permanent stop instruction.

  “Parking start” is a mode in which dead reckoning is started immediately after the start of the GPS receiver 104 or 302, the previous calibration has been calculated, and this time, for example, is taken out from a non-volatile memory. The parking lot start is useful when the vehicle 110 is activated in the parking lot and GPS reception is not good.

  Parking start requires that a special GPS off command had to be executed at the previous shutdown. This off command is referred to herein as a “permanent shutdown” command. If received, the bits are stored in non-volatile memory with various calibration parameters indicating that a parking start is to be performed at the next GPS-on event. It is reasonable to assume that the GPS receiver 104 or 302 has not been moved between sessions. If such a prerequisite is met, the new session can be considered accurate from the beginning. This is because the previous position and course provided a valid starting condition for the new session.

  The accuracy and accuracy of the heading offset and the sum of all dead reckoning delta heading data depends on how it belongs to all CANbus data generated when the vehicle 110 is moving. Thus, after the vehicle 110 is parked and cannot move, the GPS receiver 104 or 302 should simply be turned off. The GPS receiver 104 or 302 should be enabled to run and execute before the vehicle 110 moves again, so the GPS will receive and buffer important CANbus data on the CANbus 130. Don't miss out.

  The CANbus data must be time stamped in real time so that short outages or gaps can be recognized and corrected. Data should not be collected and pushed into the GPS receiver 104 or 302 asynchronously without properly stamping the data. Close sharing of the GPS system and CANbus time domain is not required in embodiments of the present invention. The timestamps on the collected CANbus data are interpolated and averaged to reduce timestamp noise and to mitigate any time drift effects between the GPS and CANbus clocks.

  Some dead reckoning embodiments can only accept 10 Hz wheel rotation increments, so the time stamp error should be less than 50 milliseconds. The recommended change in time stamp should have a standard deviation of less than 10 milliseconds.

  The rapid availability of the GPS course is a critical factor in how quickly and accurately the system 100 can calibrate and recover from a CAN pause, wheel slip, or other abnormal event. Making the course first available is necessary to compute all other calibration parameters.

  The basic worst case course error model (unit: degree) is calculated as arctan (speed error / speed). The course cannot be determined by the GPS receiver 104 or 302 when the vehicle 110 is not moving. This is because the ratio makes a round and returns. However, it is possible to determine the course at a low speed depending on the accuracy of the speed estimation value and depending on the magnitude of an arbitrary speed error. The speed error is modeled as the GPS carrier Doppler measurement noise multiplied by the horizontal accuracy drop rate (HDOP).

  Doppler measurement noise depends primarily on signal strength or signal-to-noise ratio (SNR). Any interference caused by the reflected signal in the “urban canyon” increases the true measurement error, resulting in speed and heading errors. The GPS receiver 104 or 302 is frequently operating to remove such errors from its measurements.

The conservative course error model for four different signal conditions is
A desirable model of 44 dB-Hz,
An undesirable model of 34 dB-Hz,
The estimated speed error assuming a metallized cabin and range model of 28 dB-Hz and another out-of-specification model of 24 dB-Hz, with HDOP = 6, is 0.02, 0.2, 1.. 2 and 2 km / hr.
A brief overview is
Course error <44 dBhz, 1 ° at 2 km / hr;
Course error <34 dBhz, 1 ° at 12 km / hr;
Course error <28 dBhz, 3 ° at 23 km / hr;
Course error <24 dBhz, 3 ° at 40 km / hr.

  Embodiments of the algorithm of the present invention use these models and observe the stability of the course itself to determine which courses can be included in the calibration parameters.

  The course offset should be determined within 5 seconds as long as the speed is 20 km / hr or more at the best conditions. For a metallized cabin characterized by an average SNR of 28 dB-Hz, the parameters are still calibrated at a lower speed, but the accuracy is reduced. However, continuous filtering may be used to reduce heading errors.

  A stop instruction called “permanent stop” is defined herein and referred to in FIG. It stops the GPS receiver 104 or 302 and is used as a flag to save the course calibration from one fix session to the next fix session, filling the gap over the power off period. Permanent shutdown is necessary to avoid chaos shutdown. In a conventional implementation, a normal stop command is issued and the vehicle 110 can move again before obtaining the next start command. As a result, the last position and course are no longer valid. Therefore, here the course offset is declared invalid for a general stop command. A permanent shutdown should be activated to indicate that the vehicle 110 has stopped and will not move again until the next “start” command is received.

  Some conventional code libraries need to be unable to send CANbus data to the GPS receiver 104 or 302 before initializing the GPS core with the previous execution information. Any CANbus data is received before reading the calibration from the memory declaring such CANbus data that is not calibrated. CANbus data is ignored until the previous execution data is read. Here, there is no restriction on the timing of CANbus data and the reception of the previous executable file. That is, the data is processed as soon as calibration is received, and the course offset is maintained if it was previously available.

  FIG. 4 represents the CANbus data flow and timing relationship for starting and permanently stopping the GPS receiver. There are three stages 401-403 in operation. In step 401, the GPS receiver 104 or 302 is off, but CANbus data from the CANbus 130 is present. The data can be presented to the GPS receiver 104 or 302 in the usual way, even if it has not yet started. Step 410 receives an engine on command, which means that navigation is required. Step 412 activates the host CPU (see FIG. 7) and starts receiving CANbus data. Step 414 provides a GPS application that runs on the host CPU with a pointer in non-volatile (NV) memory to previous execution information. Step 416 loads the initial factory manufacturing parameters that are typical for the vehicle model and configuration. In step 418, the GPS application and hardware are started by the START instruction and read into the nonvolatile memory. Step 420 represents the reading and writing of non-volatile memory.

  Previous execution data is not saved during dead reckoning in step 401 of the CAN flowchart. Although sector erasure is ultimately required when available storage space is consumed, such erasure makes it difficult for the dead reckoning system to keep up with the input of CANbus data. This is because erasure of the sector monopolizes the system instruction bus while erasure is being performed. Remembering previous executions during a session is meaningless. This is because the only valid storage time is when the vehicle 110 is stopped and will not move again until the next fix session. Otherwise, it is impossible to maintain the accuracy of the next parking session.

  In step 402, GPS receiver 104 or 302 is activated and dead reckoning is available at step 422. Step 402 ends when step 424 receives an engine off command.

  In step 403, the GPS receiver 104 or 302 is stopped with a permanent shutdown instruction in step 426. Step 428 represents updating the non-volatile memory with DR propagation data. CANbus data may still reach the GPS receiver 104 or 302, but they are ignored.

  FIG. 5 represents an ongoing calibration process 500 that continually mixes various sources of calibration data with the real-time calibration provided by the GPS receiver 104 or 302. This is a tight coupling of GPS and dead reckoning. The real-time calibration contribution increases the overall confidence level of the calibration status that has Status-1, Status-3, Status-4, and Status-7 levels. For example, the calibration is performed by adding 2 to the parameter B, adding 1 to the parameter A, and adding 4 to the course offset. The highest confidence level (Status-7) is the desired state, and only dead reckoning results are available to the user.

  Don't get lost between factory parameters and partial calibration. Factory calibration inputs the previous execution data when the previous execution data is empty or cleared. Therefore, since the actual calibration starts to catch up with the expected estimate based on the initial production value, the Calibration Status-7 is not lost. Since manufacturing data is mixed with real-time data, partial calibration prior to the first full calibration is not lost. This process continues until all manufacturing estimates are overwritten with real-time data.

  In step 502, if there is no previous run or factory parameter, the dead reckoning status parameter is advanced from “0” to an initial state where the parameter is not calibrated. In step 504, the status is increased to “2”, where the calibration parameters for delta range “B” are calibrated to determine the left and right wheel radii and ratios. In step 506, the dead reckoning status parameter is increased to “3” when the calibration parameters of the delta heading and delta range “A” and the physical parameter track width (TW) are calibrated. The delta range must be calibrated before calibrating the delta course.

  In step 508, the dead reckoning status parameter is increased to “7” when the course offset, delta course and delta range are calibrated. Dead reckoning and combined mode are available at step 510 as wheel radii, ratio and track width have been validated from GPS data.

  In step 512, dead reckoning and calibration continues from its starting point if calibration is available from the previous session and is retrieved from non-volatile memory. In step 514, dead reckoning is immediately available in step 510 if Status-7 was previously reached and the previous session was terminated with a permanent stop command. If the calibration parameters are enabled by GPS data at step 518, the combined mode is available at step 516.

  An alternative calibration method relies on an application programming interface (API) (see FIG. 7, eg, factory parameter mode or manufacturing mode). Most users prefer to make dead reckoning available as quickly as possible. In step 520, if the previous run data is empty or absent, such factory parameter mode provides approximate initial physical parameters for wheel radius, track width and CPR. These physical parameters are converted into A and B calibration parameters, thereby producing calibration Status-3. Only a brief observation of the GPS course at 3 meters or more per second is required to raise the calibration to Status-7, and dead reckoning navigation is then available.

  It is impractical to expect the highest dead reckoning accuracy (Status-7) in API factory parameter mode. This is because the wheel ratio and track width cannot be fully calibrated at the factory for individual vehicles 110. The wheel radius ratio and the track width must be known to be better than 1% error. The empirical measurement provided by the GPS receiver 104 or 302 is a practical answer for obtaining a sufficiently good measurement. For this reason, the combined mode operation must be postponed until the full set of calibration parameters is accurately determined using GPS calibration data.

  A typical sequence starting in the production mode of step 520 starts with Status-3 as the initial state. Assume that the radius and track width of the left and right wheels are calibrated. The manufacturing mode cannot specify a different radius for each wheel. Therefore, the composite mode is not available until calibration is confirmed. Status-7 occurs when the course offset is calibrated. Dead reckoning is available, and combined mode is only available after calibration is confirmed in step 518. Confirmation requires the same conditions as calibration at cold start.

There are a few minimum vehicle drive requirements necessary to operate the GPS receiver 104 or 302 sufficient to provide calibration information for parameter A, parameter B, and course offset. These are summarized in Table III. These are also reflected in steps 522 and 524 in FIG.

  Continuous calibration maximizes the life of the vehicle 110. The raw data is pre-filtered and verified before being processed by the main Kalman filter estimator for each calibration parameter. In general, good calibration can be maintained forever as long as previous run data is maintained (eg, in non-volatile memory). If the previous run data is completely lost, the original production value can be used as a starting point, so that dead reckoning can be made available as soon as possible.

これらの種類のＣＡＮ誤りは、基本的にStatus-3にキャリブレーション・ステータスを低下させる。従って、ＡおよびＢキャリブレーションは失われない。推測航法および複合モードは、誤りが補正され、新しい針路キャリブレーションが達成された後で直ぐに利用可能である。 There are certain conditions that reduce the calibration status to Status-7 or lower. First, as summarized in Table IV, there may be an error in the wheel rotation increment (CANbus data).

These types of CAN errors basically lower the calibration status to Status-3. Thus, A and B calibrations are not lost. Dead reckoning and compound modes are available immediately after errors are corrected and a new course calibration is achieved.

In addition, the calibration status may be lowered due to a calibration error. The algorithm should be constructed to minimize these occurrences until they are very rare. Advanced pre-filter logic is implemented so that the above conditions do not occur randomly or in noise calibration measurements. The most likely event that causes a calibration error is an incorrect calibration at the factory (see Table V).

  FIG. 6 illustrates the interrelationship between the fix mode state machine 600 and dead reckoning single mode 601, composite mode 602, and GPS single mode 603, depending on the availability of GPS assets and wheel data calibration. . The fix mode state machine 600 can be used to implement the mode selector 314 in FIG.

  In dead reckoning only mode 601, the test 604 checks whether a GPS fix is available from the GPS receiver 104 or 302. If yes, the test 606 asks if there is an excessively long GPS outage (outage) or if the position change (delta position) is large. If yes, the operation switches to the GPS single mode 603.

  However, if not, the test 608 asks whether dead reckoning parameter calibration is available and confirmed. If yes, the combined mode 602 is allowed. Otherwise, the operation must switch to GPS only mode 603. While in combined mode 602, two tests are constantly performed. Inspection 610 determines whether two or fewer satellite vehicles are available. If true, the quality of the GPS solution is not sufficient and the operation must be switched to dead reckoning single mode 601. This may occur when the vehicle 110 enters the tunnel.

  Another test that is constantly performed in combined mode 602 is a test 612 that checks whether there are many consistent satellite vehicles. If so, the GPS result is very strong and it is better to switch to the GPS single mode 603. While in the GPS only mode 603, the test 614 checks to see if there are many consistent satellite vehicles. If so, the GPS result is very strong and the operation can continue in the GPS only mode 603. Test 616 asks if two or fewer satellite vehicles are available and whether calibration is available. If so, operation switches to dead reckoning single mode 601.

  The fix mode state machine 600 is activated at step 620 when the hardware for the tightly coupled GPS and dead reckoning navigation system 100 is first activated. Test 622 determines whether a permanent stop bit has been set (eg, in non-volatile memory). If so, step 624 checks whether calibration data is available. If yes, the operation begins in dead reckoning alone mode 601 and the GPS receiver 104 or 302 can come out in the background without delaying the display of the vehicle navigation solution to the user, but If not, step 626 asks if a GPS fix is available. Otherwise, wait for loop 628. When GPS fix becomes available, operation switches to GPS only mode 603.

  In outdoor conditions, if the previous data including ephemeris, location and time is available and still fresh, the first positioning time (TTFF) of 1 second warm-up is possible with GPS . However, in a vehicle 110 for automotive applications, the GPS signal may be shaded by vehicles in the parking lot or cannot be initiated from a GPS warm start condition. Thus, activation must begin at parking mode step 630.

  Even if the vehicle 110 is outdoors, if the ephemeris data is considered too old, a “parking lot” activation will occur, but as long as good dead reckoning data is available, for example, complete calibration 7 and the permanent stop bit are available and dead reckoning single mode 601 can start within 1 second. Parking mode 630 is best included in systems that do not have a battery supported by a 32 kHz real time clock (RTC) that helps track GPS time better than 1 millisecond.

  If sufficient calibration or permanent stop bits are not available, parking mode 630 is not available during the session and the first fix is generated only after a new GPS fix is computed.

  In parking mode, dead reckoning always starts from the previous position. However, the accuracy of that determination cannot be determined until the first GPS fix is available.

  As soon as the first GPS fix is available, the vehicle 110 may have been moved while the GPS receiver 104 or 302 was off, so a determination as to whether the current dead reckoning position should be trusted. Must be made. For example, when the vehicle 110 is transported on a ferry boat, the delta position from the new GPS fix and the latest dead reckoning navigation are performed. For large distances, a GPS-only fix is chosen to reach an accurate position solution as fast as possible.

  If the distance traveled by the vehicle 110 is not large, the fix will be in either the GPS only mode 603 or the combined mode 602 depending on the GPS measurement and the relative accuracy of the dead reckoning fix being conveyed. A highly reliable GPS measurement or lower accuracy dead reckoning forces the state machine 600 into the GPS only mode 603, while a less reliable GPS data forces a more complex mode 602.

  In order to use combined mode 602, calibration must already be enabled. This is always the case when factory parameters are used. This means that the combined operation mode 602 cannot be obtained for a short operation year (for example, before the vehicle is sufficiently operated so that the calibration capability is observed).

  In the general case after calibration is enabled, the fix mode is the dead reckoning single mode 601 when two or fewer navigation satellites are available. If the number of navigation satellites is greater and the estimated multipath is lower than the estimated dead reckoning calibration accuracy, the fix is in the GPS only mode 603. If the number of navigation satellites is not large, or if the estimated multipath is higher than the estimated dead reckoning calibration accuracy, the fix becomes a composite mode 602.

  The determination of the fix modes 601 to 603 is made continuously, and the selected modes 601 to 603 can be changed every second. GPS and dead reckoning conditions are always estimated to determine whether a transition to combined mode or GPS alone mode provides better results. For example, if the last mode is the GPS only mode 603, the increased multipath environment or the decrease in navigation satellites is a good reason to move to the combined mode 602.

  Similarly, if the current mode is combined mode 602, the condition is always estimated to determine whether the transition to GPS only mode 603 provides better results. If the current mode is dead reckoning single mode 601 and more than two satellites are available, a transition to either GPS single mode 603 or combined mode 602 occurs. For short pauses where the dead-reckoning error integral is small, the transition is to composite mode 602. However, for longer rest periods, the GPS-only mode 603 is likely to be temporarily selected to quickly snap to an unbiased position estimate. However, only a small number of fixes in the GPS only mode 603 is necessary to restore the best accuracy. In general, the fix mode returns to the composite mode 602 unless the number of navigation satellites is large and the estimated multipath error is not small compared to the estimated calibration accuracy.

  The information update rate is as fast as 1 Hz and provides a “super coupling” characteristic that is used to describe a GPS and inertial navigation integrated system. Dead reckoning and GPS information are combined in a main position / velocity Kalman filter. Dead reckoning measurements of delta range and delta heading are directly combined with GPS Doppler and pseudorange measurements.

  It provides the characteristics of the “tight” coupled approach of GPS and inertial navigation combined system 100, and GPS and dead reckoning position and velocity estimates are calculated independently and then share information to help each other It works better than the “loose” coupled solution combined in the position / velocity region without.

  Continuous calibration continues when in combined mode with parallel calibration methodology. Independent speed and course estimators are used for continuous calibration reference of CAN calibration parameters, regardless of whether the position is calculated in GPS single mode or combined mode.

  Three position modes 601-603 are used instead of only two. The basic DR input data has one step quantization (eg, 5.6 cm for a 17 inch wheel with 48 steps). Some sensors skip outputting ticks at low speed. Pause periods, wheel slips, and missed CANbus packets may occur. Blunder checking and filtering can be applied to correct most errors prior to use, but cannot be used for calibration.

  The synchronization of the wheel rotation increment time may change depending on the load of the CANbus 130 and the host CPU. Wheel increments are biased against banked roads. Tires can vary in size with respect to temperature, speed, and age. Dead reckoning detection and processing varies from manufacturer to manufacturer and thus has different error characteristics. Furthermore, the accuracy of dead reckoning strongly depends on the quality of the calibration. Even a 1 degree course calibration error may be integrated into a large position error for a given sufficient distance of movement. Position based on dead reckoning is essentially an integral of the derivative (delta heading and delta range). Thus, the integration will have an unknown integration constant or error from the true delta position. Thus, dead reckoning wheel rotation step integration is always biased and dead reckoning navigation cannot provide absolute positioning capability.

  GPS sensors have a completely different set of advantages and disadvantages. GPS carrier phase observation can measure better than 5% of the carrier wavelength (0.05 * 0.19 m <1 cm). They average the Doppler of 50 phase measurements per second from the 50 Hz phase lock loop to reduce the carrier phase standard deviation to 1 mm / sec. The integration of the GPS carrier frequency is much more accurate than trying to integrate the wheel rotation increments. The GPS pseudo-random code phase provides an absolute position. The code phase wavelength is 293 m, but can be measured with an accuracy of 1 m in the absence of multipath interference. The vulnerability in urban areas is that GPS suffers from multipath and pure reflection.

  Given the advantages and disadvantages of dead reckoning sensors and GPS sensors, the GPS only mode 603 is used to recover the fastest from a pause in GPS signal reception that imposes a longer period of operation in the dead reckoning mode 601. Dead reckoning mode 601 cannot measure an absolute error and can measure only a position change. Thus, any combination of dead reckoning data simply slows recovery from GPS pauses. The GPS only mode 603 is used to determine the best absolute accuracy when the GPS situation is favorable without compounding the integration bias from dead reckoning and CANbus data errors such as wheel slip and quantization errors. Is done.

  The GPS only mode 603 is used to provide a more robust solution across multiple dead reckoning systems. The implementation of each manufacturer's CAN bus is slightly different and varies with the various types of vehicles sold worldwide. Since the composite mode 602 is used only when the GPS error is larger than the dead reckoning error, maximizing the use of the GPS single mode 603 hides the difference.

  Composite mode 602 is used to stabilize the GPS-based position solution in the presence of high multipath or high horizontal accuracy reduction (HDOP) due to few usable navigation satellites. Composite mode 602 is used to maintain high GPS accuracy when entering a dense urban canyon.

  The relative weight of the combined mode 602 relative to the GPS only mode 603 balances between the absolute accuracy of the GPS solution and dead reckoning accuracy. This advantage can change in as little as a second.

  In general, in the outdoor state, the best navigation performance is due to the GPS only mode 603, and the GPS carrier phase measurement is more accurate than the wheel sensor. In urban situations, the best navigation performance is due to the composite mode 602 because the effects of multipath and reflected noise exceed those of dead reckoning noise.

  GPS chipsets and modules without an in-vehicle processor are classified as measurement platforms (MP) and provide data to the host processor through a serial UART connection. The host CPU executes navigation software that calculates position and course information. Such navigation software hosts independent of compatibility with a wide variety of other host platforms including other commonly available microprocessors such as ARM, Strong ARM, Pentium®, SH Mobile, Samsung, etc. An operating system. Modules and chipsets with onboard processors are categorized as position, velocity, and time (PVT) solutions and provide sufficient navigation capabilities in standard NMEA or dedicated formats. The navigation software is embedded in a module or chipset.

  FIG. 7 represents an embodiment of the ultra-tightly coupled dead reckoning subsystem of the present invention, referenced here by the general reference numeral 700. FIG. 7 further shows details of some possible implementations of the items shown in FIGS. 1, 2 (a), 2 (b) and 3. 2 (a) and 2 (b) distinguish between implementations of functional element parts in hardware or software, where the functional interrelationship is represented in FIG.

  An orbiting navigation satellite 702 transmits a microwave signal that is received by a navigation measurement platform (MP) 704 (eg, the eRide (San Francisco, Calif., OPUS-III nanoRide GPS module with serial output)). And demodulated. The MP 704 includes a 32-channel radio frequency (RF) receiver, baseband, and SAW filtering stage. The MP 704 can be a two-channel real-time differential GPS with a geostationary satellite-type satellite navigation augmentation system (SBAS). These connect through the hardware interface 706 and provide a time report 708, a fix trigger 710, and a Doppler and pseudo range report 712.

  In the PVT-type implementation illustrated in FIG. 2 (b), CANbus 130 data is brought in by CANbus driver 714 and UART 716, time stamped at device 718, and converted at device 720. An application programming interface (API) 722 inputs CANbus data. Instead, in the MP type illustrated in FIG. 2A, CANbus information having an appropriate time stamp is provided by the host application 724.

The CAN buffer 726 processes new wheel step data and buffers it for several seconds. _Here, C L, _{C R} is the number of increments accumulated in CANbus packets for each of the left and right wheels over a 100 msec. The number of wheel ticks is generated by taking the difference between the current CANbus packet and the previous CANbus packet because the content of the CANbus packet is an accumulated number. This data is used by dead reckoning (DR) propagation processor 730 to produce estimates of delta-range, delta-heading, and delta-heading-sum. The The DR propagation processor 730 forms a DR error model 732.

DR calibration apparatus _734, A _L, includes A R, _{B L,} and a Kalman filter for _{B R.} The A _L and A _R calibration parameters represent the delta-heading / tick difference for the left and right wheels (for example, units of minutes / tick = angle * 60 / tick). B _L, B _R is a calibration parameter of the delta-range / tick for left and right wheels (e.g., units of mm / tick). The course offset is a calibration parameter that translates the total delta course to a known course reference.

  The Kalman filter 736 handles delta range and delta course, and composite mode propagation from position, velocity, parameter B, delta range and course D, and time. Mode selection process 738 is detailed in FIG. 6 as process 600 and is represented as selector 314 in FIG.

  Data processing 742 provides the position solution encoded in the NMEA navigation message. Calibration status message 744 and NMEA message are connected to output API 746. In the PVT 250 implementation of FIG. 5, the NMEA navigation message and the calibration status message are output by UART 747. Otherwise, in the MP200 type implementation of FIG. 5, the NMEA navigation message and calibration status message are output to the host computer application 724 through the software interface.

  The application time offset calculation is provided in an offset calculation process 748 to CANbus data time, and a GPS receiver internal timer is further required for proper dead reckoning mode. This requires a 1 millisecond precision timestamp to receive both CANbus packet data and a callback function to read the CAN timer. However, offset calibration is automatic and proceeds from receipt of the first CAN data packet. This necessary calibration step does not prevent entering dead reckoning mode with the first CANbus data packet after a valid calibration.

  GPS receiver 104 or 302, and 700 communications are defined in the NMEA specification. Most computer programs that provide real-time location information understand and expect that their data will be in NMEA format. This data includes the complete position, velocity, and time (PVT) solution computed by the GPS receiver. The NMEA sends a line of data called a “sentence” that is completely self-contained and unrelated to other sentences. There is a standard statement for each device category, and there is also the ability to define dedicated statements used by individual companies. All standard sentences have a two-letter prefix that defines the device that uses the sentence pattern. In the GPS receiver, the prefix is GP. The prefix character is followed by three consecutive characters that define the content of the sentence. NMEA allows hardware manufacturers to define their own sentences that begin with the letter P and are followed by three characters that identify the manufacturer. For example, Garmin's sentence begins with PGRM and Magellan's sentence begins with PMGN.

  Each sentence can begin with a “$”, end with a carriage return sequence, and be 80 or fewer characters of visible text (in addition to a line terminator). Data is contained within this single line with data items separated by commas. The data itself is simply ASCII text and can extend across multiple sentences in some specialized examples, but is usually contained entirely in one variable length sentence. Data may vary in the amount of accuracy included in the message. For example, the time may be indicated as a fraction of a second, or the position may be indicated with 3 or 4 digits after the decimal point. Programs that read data should simply use commas to determine field boundaries and are independent of column position. There is provision for a checksum at the end of each sentence, which may be checked by the unit reading the data. The checksum field consists of one “*” and two hexadecimal numbers representing an 8-bit exclusive OR between all characters, but does not include “$” and “*”. A checksum is necessary for some sentences.

  Although there have been some changes to the above standards, the only ones that may be encountered with the use of GPS are 1.5 and 2.0 to 2.3. These simply specify a number of different sentence constructs, which may be specific to the needs of a particular device. Thus, the GPS may need to be changed to suit the connected device. Some GPSs provide the ability to compose a customized set of sentences, while other GPSs can provide a fixed set of options. Many GPS receivers simply output a fixed set of sentences that cannot be changed by the user. The current version standard is 3.01. The inventor has no specific information about this version, but the inventor is unaware of any GPS product that requires adaptation to this version.

  NMEA consists of a sentence and its first word, called the data type, defines the remaining interpretation of the sentence. Each data type has its own specific interpretation and is defined in the NMEA standard. The $ GPGGA statement provides essential fix data. Other sentences may repeat some of the same information but also provide new data. A device or program that reads the data can focus on the data sentences that it is interested in, but simply ignores other sentences that are not of interest. In the NMEA standard, there is no command that indicates that the GPS should do something else. Instead, each receiver simply sends all the data and expects many to be ignored. Some receivers have instructions in the unit that can select a subset of all sentences to send, and in some cases individual sentences. There is no way to indicate to the unit whether the sentence has been read correctly or to request to resend some data that is not available. Instead, the receiving unit simply checks the checksum and ignores the data if it thinks the checksum is bad and the data will be transmitted again later.

  Dead reckoning fix is reported by GPS receiver 104 or 302, and 700 in both ASCII format NMEA strings as well as functional API. Dead reckoning fix is indicated in NMEA format in the $ GPGGA string by a fix indicator value of 6. The GPS fix value is 1. Dead reckoning fix is reported by value in the functional API. Dead reckoning also provides a speed estimate by dividing the delta range by a known observation period. Both of these parameters are visible in the NMEA $ GPRMC string and also the functional API. These fields report only dead reckoning fix after valid calibration is achieved.

The calibration status can be seen in the string. Dead reckoning debug messages are available in standard NMEA format useful for detailed monitoring of dead reckoning calibration progress and status. For example, see Table VI. It is output from the core library with standard NMEA output, but the message must be sought and then sent to an output port or file.

  There is no end time associated with any saved calibration. As soon as GPS / dead reckoning is enabled by command and a CANbus packet is available, a new calibration starts. The status level of the last calibration is not affected by the calibration epoch.

Knowing the physical parameters for the vehicle 110 allows the initial calibration to enter the calibration algorithm through the API 722. The A and B parameters are initialized in accordance with the left and right radii (R ₁ , R _r ), the number of rotations per revolution (CPR), and the track width (TW). Dead reckoning mode 601 is not possible until the first GPS fix is made at a sufficient speed, so that a good course offset can be established.

  API 722 provides a manufacturing method for initializing system 700 and speeding it up as calibration becomes available, and API 722 and output API 746 allow functional system inspection of CANbus packet processing 726 and 730.

  Since the same application thread is used at the beginning of each session, data indicating which source of CANbus data is used is typically provided by the host CPU application for each GPS session. In many cases, this involves sending physical parameters. It is assumed that the physical parameters entered by the manufacturer cannot be as accurate as anything estimated during operation by the running GPS receiver 104 or 302.

  Accurate calibration requires knowing the physical parameters very accurately. Even small apparent effects of tire pressure can significantly affect the actual wheel radius and vary between day and night. For this reason, factory physical parameters should only be loaded when a previous run of GPS calibrated data has been cleared. This means that the previous GPS-based calibration is not overwritten with factory parameters through the API.

  In most manufacturing cases, it is expected that the manufacturer will not know the actual wheel radius with sufficient accuracy to provide reliable dead reckoning. For example, the tire pressure may not be full or the pressure on each wheel may not be equal.

  If the user wants to be able to use it quickly and can provide high-precision calibration, GPS will be available, and dead reckoning can be used as soon as the vehicle 110 is moved. If the manufacturer can purely provide a reasonably accurate calibration (within a few percent), the accuracy penalty is small before a full GPS-based calibration installs itself. This is the case for airbag deployment applications, where the availability of dead reckoning is initially more important than sufficient accuracy.

  In the low-accuracy factory mode, the physical parameters are used as calibration initial conditions and classified as accurate inside, but the calibration reliability observable from the outside is set to zero. Dead reckoning is available after GPS-based calibration improves the initial parameters and completes the normal calibration process. This mode is selected to speed up calibration and not allow dead reckoning until GPS calibration is complete. The time to effective dead reckoning calibration is faster than if no starting value was provided.

  Laboratory testing mode provides functional verification of software and systems and is used for laboratory testing. Before and after the inspection is completed to avoid problems in other factory modes, the previous executable is deleted. Dead reckoning is immediately available without any additional calibration. The starting course always starts from 0 and requires a starting position. The location can be installed via a location input API after sending physical parameter instructions or by obtaining a GPS fix.

  Inspection vehicle calibration can be transferred to a family of similar vehicles, where immediate dead reckoning is a higher priority than having initial accuracy. If dead reckoning is needed immediately and it is not possible to calibrate each vehicle individually in the factory, a single vehicle is selected as the representative of the family of vehicles. It is configured for factory default mode. Initial calibration is not required and the test driver can run a calibration suite to accumulate GPS-based calibrations. PERDCR, 11 NMEA messages such as Table VI are enabled and recorded during calibration performed on the storage computer. The NMEA file is retrieved from the storage computer and the A and B calibration parameters are extracted from the final PERDCR, 11 string. The physical parameters are estimated from the calibration parameters. The physical parameters are loaded at the factory during installation and the factory high-precision calibration function is selected. The host CPU application is configured to read physical parameters from a file, or they are hard coded into the host CPU application. The vehicle family can then observe rapid dead reckoning as soon as the initial GPS fix is obtained at a sufficient speed (eg, 25 km / h or more).

Simple mathematics is used to estimate physical parameters from calibration parameters. The estimated calibration parameters are easily retrieved from the dedicated NMEA string PERDCR, 11. The calibration parameters observed in PERDCR, 11 have the following units and sizes.
A _L = R _l / CPR / TW * 360 * 60 (minutes / tick);
A _R = R _r / CPR / TW * 360 * 60 (minutes / tick);
B _L = R _l / CPR * PI * 1000 (millimeters / tick);
B _R = R _r / CPR * PI * 1000 (millimeters / tick)
The estimated calibration parameter from PERDCR, 11 is defined by:
A _L '= estimate of true A _L ;
A _R '= estimate of true A _R ;
B _L '= estimate of true B _L ；
B _R '= estimate of true B _R
The physical parameter (TW) of the track width is estimated by the following equation.
TWl '= B _L ' / A _L '* (360 * 60) / (PI * 1000) (meters);
TWr '= B _R ' / A _R '* (360 * 60) / (PI * 1000) (meters)

The calibration algorithm ensures that the B / A ratio for both wheels is the same. Either left or right wheel parameters can be used. Another approach is to average these two estimates, resulting in:
TW 'estimate = (TWl' + TWr ') / 2
Unfortunately, the wheel radii (R _l , R _r ) cannot be separated from the number of revolutions per revolution (CPR). These parameters are always combined as in the above formula. Each vehicle manufacturer supplies CPR in a set of physical parameters. In this case, the wheel radius is estimated as follows.
R _l = B _L '* CPR / PI / 1000;
R _r = B _L '* CPR / PI / 1000

Embodiments of the real-time calibration method of the present invention have three steps: (1) compare the delta range with GPS speed and estimate B _L and _BR parameters; (2) B parameters given compares delta heading and changes in the GPS course, estimates the a _L and a _R parameters; and (3) gives a and B parameters, used as an absolute reference for the GPS course can estimate the course offset Is done.

  Before the dead reckoning fix can be computed, there must be: (a) a valid calibration of parameters A and B, course offset, (b) a valid position, and (3) Input of CANbus data packet with synchronized time stamp.

  The GPS receiver 104 or 302 does not require an estimate of GPS time in order to operate the dead reckoning single mode 601. This allows the “parking mode” to proceed even if the GPS receiver 104 or 302 is not providing time information. A valid calibration as represented by previous run data 750 in FIG. 7 can be provided either from non-volatile memory data or input through an API.

  Dead reckoning calibration starts automatically, for example, as soon as any CANbus packet is received, without initialization from the API command. The time for available calibration depends on the availability of GPS data and the completion of straight ahead and turns including large course changes. The time to be calibrated is reduced by the higher speed. This is because more steps can be observed and the quantization effect is proportionally weakened.

  Calibration of the B parameter, wheel radius, and ratio requires either a straight segment or a straight run of the GPS receiver 104 or 302, where the course changes, such as figure 8 or straight run. Canceled. The minimum requirement is to run at least 5 such segments. Thereafter, the A calibration calculates the track width, and then proceeds to execute the turn. Right angle turning is better than at least 5 circles. The course offset can then be calibrated after parameter A and parameter B are obtained.

  Thus, the minimum requirement to collect and generate calibrations is to obtain at least 70 meters straight segments without significant acceleration, at least 5 right angle turns, and at least 3 meters per second for 5 seconds to obtain a course offset. It is a straight line segment. Such an example has an undesirable signal level of 34 dBHz.

  Wheel rotation step sensors 120, 122, 124, and 126 (FIG. 1) are generally Hall-type devices, such as a digital clock step as the wheel rotates and the magnetic bumps pass through the detector. Create electrical nicks. The number of ticks generated for one revolution of the wheel ranges from 48 ticks for Peugeot cars to 98 ticks for Mercedes cars.

  The original string of wheel rotation ticks produced by the sensor is continuous, but CANbus 130 must inevitably bundle the wheel ticks into 1-10 millisecond data packets for multiplexing. . Secondary processing groups these shorter packets into longer packets that each span 100 milliseconds (eg, 10 Hz rate). These 10 Hz CAN wheel rotation step packets are accessible by external applications through a protective gateway between the secure life safety network and the external application network.

  The CANbus 130 has a processor (CPU) with a system clock that is used to generate a sampling range of wheel rotation ticks. Such CPU clocks are generally not available externally for synchronization, so the time domain between 10 Hz packet generation and any GPS receiver clock must be handled asynchronously.

  In embodiments where the CANbus and GPS receiver clocks can be synchronized, carrier Doppler, code phase, and other GPS observations can be taken over the same time range. It is a good way to synchronize from master to slave with 1 pulse / second (1-PPS) pulse. Another embodiment uses the same clock or time difference or frequency difference circuit to observe the relative time or frequency difference between the two clock domains. Although the OPUS ™ baseband chip from eRide (San Francisco, Calif.) has such capabilities, its use dramatically complicates system integration.

  Synchronization of CANbus data is further complicated by the delay inherent in the transmission of packet messages over a network such as CANbus 130 and GPS receiver 104 or 302. Typically, the third CPU is physically connected to the CANbus 130 and converts from the CAN protocol to a dedicated protocol. This is because all manufacturers use different CAN message protocols and wheel rotation ticks. Such a CPU converts to a common format for the CAN input of the GPS receiver. There are three types of delays: (1) generated from the delay of the CANbus 130, (2) generated from the delay of the CAN format converter, and (3) the reception buffer included in the GPS receiver 104 or 302. Outbreak. The combination of these delays is called “CANbus jitter” and has an invariant part and a variable part.

  The combination of CANbus jitter and any time drift between the CANbus clock and the GPS clock creates a noise factor in the synchronization and processing of CAN and GPS data.

  Synchronization is obtained by stamping each CANbus packet as it arrives at the GPS receiver buffer through a universal asynchronous transceiver (UART) serial interrupt driver.

  The GPS receiver software running as the host CPU program must select which packet is closest in time to the GPS time range in order to use the CANbus data for both calibration and dead reckoning propagation. A typical range is 1 second. There are typically 10 packets with time tags within each GPS one second time range.

  In car experiments, the time tag shifted rapidly and in just a few minutes, it actually became 11 packets, indicating that the CANbus clock was running fast, or 9 packets and CANbus. Indicates that the clock has run slowly. Furthermore, CANbus jitter is seen to be responsible for 9 or 11 packet variations, typically with a 1 second acquisition operation.

  Such a problem has a simple solution. First, the offset between the start time of a noisy packet and the GPS range time is filtered to remove most jitter. The average difference is maintained. It is biased with a drift component, so the filter is configured to track changes. The original time tag with jitter is used to select packets that include both start and end intervals in the GPS time domain. The average difference is then used to define the portion of the packet that has a GPS fix time. The contribution of packets within the GPS interval is interpolated from the total number of packets.

  For example, in a packet having a GPS start time, a portion earlier than the GPS start time and the scheduled packet time is interpolated, leaving a portion generated after the GPS time by subtracting the average difference. Similarly, for packets that have data that occurred after the GPS end time, interpolation assumes the used portion and uses the average difference from the GPS end time to the scheduled packet start time. Remove any period after time. Other packets between these two boundary packets are used in their entirety.

  Such techniques are used for ticks from both the left and right wheel sensors 124 and 126 so that the interpolated wheel rotation ticks are adjusted to best match the corresponding GPS time interval. .

  The GPS start time and end time are different for each formula of delta range and delta course. In the delta range measurement, a GPS speed of 1 second or more is compared at the same interval with all wheel rotation increments. Since the GPS carrier tracking wavelength is 0.1904m, a 1 second integral of GPS speed is used, which is determined within a few degrees using a conventional phase-locked look method common to GPS-based speed determination. The On the other hand, the GPS code phase has a wavelength corresponding to one chip of 293 m. Therefore, the 1 second delta range from the code phase is too noisy for a short time calibration.

  Long time calibrations with GPS derived position solutions are possible, but they require extensive processing and memory.

  The preferred embodiment uses east and north speeds from the GPS speed solution as the main calibration source. The delta range from GPS is defined as the square root of the sum of the east speed squared and the north speed squared. The course is defined as the quadrant result of the inverse tangent (arc tangent) of the eastern speed divided by the northward speed. The east and north velocities include both positive and negative signs and magnitudes.

  The GPS east and north velocities themselves are estimated from GPS Doppler measurements. The Doppler measurement is the average of the carrier Doppler frequency divided by the measurement interval. The applicable time for the measurement is the center of the above range.

  In delta range calibration, wheel rotation increments are selected by start and end times that approximate the start and end times of GPS measurements.

  The speed fix is centered on a one second range defined by a time tracking state machine (TSM) measurement. The GPS fix course is applied to the center of the TSM range. Timing is assumed that the transition from GPS to DR does not cause time tag jumps.

  Left increment (TL) and right increment (TR) are defined as 1 second wheel increments. In the course, TL and TR have a time range from the center of the previous range to the center of the new range.

The coefficients are as follows.
A _L = RadiusLeft / CPR * TRACKWIDTH * degree * 60 (minutes / tick);
B _R = RadiusLeft / CPR * 1000 (millimeters / tick)

The one second delta course is as follows.
δh = A _L * TL-A _R * TR
And
A _L = A + dA
A _R = A-dA
δh = (A + dA) TL-(A-dA) TR
= A * [TL-TR] + dA * [TL + TR]
When DH = 0, the arc is closed for a while or is running straight, as judged from GPS measurements.

next,
A _L * TL = A _R * TR
A _L / A _R = TR / TL
α = A _L / A _R = (A + dA) / (A-dA)
Make (1-α) / (1 + α) and solve as
(1-α) / (1 + α) = -dA / A
Therefore, dA = -A (1-α) / (1 + α)

In the delta range, the wheel increment is defined as the increment of raw data over the same time frame as the TSM range.
δh = A * [TL-TR]-(1-α) / (1 + α) * [TL + TR]
= A * [(TL-TR)-(1-α) / (1 + α) * (TL + TR)]

The 1 second delta range is as follows.
dr = B _L * TR + B _R * TR
And
B _L = B + dB
B _R = B-dB
as a result,
dR = (B + dB) * TL + (B-dB) * TR
= B * (TL + TR) + dB * (TL-TR)

By the definition of _{B L} and _{B R} in the physical parameter,
B _L / B _R = A _L / A _R
Therefore,
dB = -B (1-α) / (1 + α)
dr = B * (TL + TR)-B (1-α) / (1 + α) * (TL-TR)
dr = B * [(TL + TR)-(1-α) / (1 + α) * (TL-TR)]
To calculate dead reckoning fix that propagates the position by 1 second from the previous fix time,
deltaN = dr * cos heading (delta-north);
deltaE = dr * sin heading (delta-east);
heading h (t _i ) = h0 + Σdh _n (n = 0, i)
It is.

_{A L, A R, B L} , and assuming that the estimated notarized calibration _{B R,}
1) To estimate α, find the segment of the orbit where + Σdh _n (n = 0, i) GPS is zero. In this case, the ratio of steps from right to left is defined as follows.
a. α = TR / TL
2) In order to estimate B, the same wheel increment is obtained from the estimated value of dr from GPS and the same observation range as the GPS range change observation range.
B = dr / [(TL + TR)-(1-α) / (1 + α) * (TL-TR)]
3) In order to estimate A, an estimated value of dh is obtained from GPS, and the CAN increment is obtained from the same observation range as the GPS course change observation range.
A = δh / [(TL-TR)-(1-α) / (1 + α) * (TL + TR)]
4) To estimate h0, if the GPS course is reliable, maintain the difference between the sum (dh) and the GPS course.

The DR, which is stable for a short time and unstable for a long time, is unstable for a short time, and stable for a long time, is obtained using point observation. These observations are each derived from velocity information that is an intermediate value of 0, but the integration is not stationary. In order to obtain a final calibration that is stationary, information from the GPS location is required.

For long time observation of dE and dN from GPS,
DE _gps = ΣdE _gps
DN _gps = ΣdN _gps
With a similar estimate formed from a short-calibrated DR,
DE _dr = ΣdE _dr
DN _dr = ΣdN _dr
It is. In a similar estimate formed from a short time calibrated DR, a total of 3 points is used, for example.
DE _dr = ΣdE _dr
= dr1 * sin (h0 + dh1) + dr2 * sin (h0 + dh2 + dh2) + dr3 * sin (do + dh1 + dh2 + dh3);
DN _dr = ΣdN _dr
= dr1 * cos (h0 + dh1) + dr2 * cos (h0 + dh2 + dh2) + dr3 * cos (do + dh1 + dh2 + dh3)
The estimates of A and B are assumed to be sufficiently accurate so that a first order Taylor series can be used.

Embodiments of the present invention compensate for the rotational step for the speed effect phenomenon represented by curve 800 in FIG. The low speed segment 801 below the low speed cut-off is an essentially flat line. The intermediate speed segment 802 between the low speed cutoff and the high speed cutoff follows a polynomial, 1 + c _1st (sS _L ) + c _2nd (sS _L ) ² . The high speed segment 303 exceeds the scale limit of the coefficient.

  Speed related effects result in a change in the difference in the number of left and right wheel ticks in rotation with respect to speed due to changes in wheel radius. In other words, the same rotation obtained at different speeds causes a difference in the number of ticks between the left and right wheels. The cause is wheel warping and vehicle suspension reaction.

  At higher speeds, a greater amount of turning energy, seen as wheel increment differences, occurs compared to lower speeds. Of course, the higher the speed, the more ticks per second, so the wheel must compensate for the apparent angular speed calculated from the rotational ticks.

The turn ticks that enter the individual basic delta course updates must be properly compensated, where:
delta Heading = A * turn ticks
It is. The rotational increment is routinely compensated based on the difference in wheel radius when going straight.
Delta heading = Aleft * WheelTicksLeft-Aright * WheelTicksRight
= A * (WheelTicksLeft-WheelTicksRight)-alpha * (WheelTicksLeft + WheelTicksRight)
= A * compensated turn ticks
= A * compTT
It is. Rotation not compensated for
turnTicks = left wheel ticks-right wheel ticks
It is. The low speed correction (1) for segment 801 relative to the wheel radius is
compensated turn ticks (1) compTT (1) = turn ticks-alpha * sum ticks;
alpha = 1-ratio / 1 + ratio
Where “ratio” is the filtered value of the right wheel increment divided by the left wheel increment when not turning.

The correction of the segment 802 to the speed effect CompTT (2) measures compTT (1) by the following polynomial.
1 + c _1st (s-S _L ) + c _2nd (s-S _L ) ²
This is a function of total increments,
here,
s = sum ticks
S _L = Below reference point low-speed cutoff, polynomial = 1
Above the fast cutoff, polynomial = coeffScale limit.

  In delta course calibration, the difference between two consecutive GPS course observations is used, as represented in FIG. The individual head time tag is the center of the GPS measurement range. Thus, the difference between the two GPS courses has an applicable time between the two time tags of the two GPS courses. For this reason, the wheel rotation increment used for the delta course is in a different time range than that for the delta range, and the delta range is the higher speed used to form each course individually, Or, depending on whether it is at a slower speed, it can either be 0.5 seconds ahead of the delta range range or it can be 0.5 seconds behind.

  In practice, the earlier (or slower) speed1 is used for the delta range. This is because there may be a delay in receiving all CANbus packets required to extend the speed2 interval, and speed2 is on the CAN communication line (eg, CAN to converter to GPS serial port). Because it requires more rapid data.

In general, the basic formula for rotating the left and right wheels uses a scale factor that simplifies each wheel.
DH = delta-heading = A _left * ticks left for DH-A _right * ticks right for DH;
DR = delta-range = B _left * ticks left for DR + B _left * ticks right for DR
further,
DR heading = initial heading from GPS + sum DH;
When
Delta East = DR sin (DR heading);
Delta North = DR cos (DR heading)
It is.

  Experiments show that parameter estimation is not as simple as it looks. Parameters A and B are no longer constant. They change with time. This is because the wheel radius changes with tire pressure, external temperature, speed, turning effect, vehicle load, passenger arrangement and number of people, tire wear, and the like. The solution described here models each parameter as a slowly varying parameter, each corresponding to a different time model.

  Although it is possible to solve all the parameters in the multivariable nonlinear system mathematical formula, it was found that the parameters can be independently calculated by a single variable mathematical system if they are performed in the correct order.

Instead of solving each of the left and right parameters for A and B,
A _right / A _left = B _left / B _right = r
The 1-second delta course is
δh = A _L * TL-A _R * TR;
And
A _L = A + dA;
A _R = A-dA;
δh = (A + dA) TL-(A-dA) TR;

= A * [TL-TR] + dA * [TL + TR];
And r = A _L / A _R = (A + dA) / (A-dA);
Once sorted,
dA = -A (1-r) / (1 + r)
It is. Therefore,
delta-heading = A * [(TL-TR)-(1-r) / (1 + r) * (TL + TR)]
= A * compTT
It is.

Here, the compensated rotational step energy is
compTT = (TL-TR)-(1-r) / (1 + r) * (TL + TR)
It is. Similarly, when solving the common B parameter,
delta-range = B * [(TL + TR)-(1-α) / (1 + α) * (TL-TR)]
= B * compST
It is. Where compST = compensated total increment.

  A simple formulation deals with the general case where the left and right wheels do not effectively have the same radius. The bias between the left and right wheel increments accumulates even when the vehicle 110 is traveling straight.

A simple way to estimate this parameter is to use the GPS receiver 104 or 302 to isolate driving conditions in which the vehicle 110 goes straight or makes a slight turn. Under this condition, the ratio “R” can be estimated as follows over a period in which any change in the GPS course from the start of integration to the end of integration is a small change in the GPS course.
R = sum ticks right / sum ticks left
That is, the start and end periods are considered when the absolute value of (headGPSstart-headGPS) is typically below a threshold of 1 °.

  The estimate of the delta course includes any true change in the course of the vehicle 110 that causes any GPS course error and accurate turning energy in the wheel rotation increment.

  In order to provide this and all common change states, the individual r estimates are blended with a single state Kalman filter. The noise model for each measurement reveals the reliability of the two GPS course estimates. The processing noise model for the Kalman filter is adjusted to provide how fast the ratio parameter can change.

  The processing noise is always set large when the vehicle 110 is stopped for a long time. This is because changes in vehicle load can significantly affect the tire radius. Uniformizing the processing noise to a steady state allows the ratio estimate to provide a change in condition every 5 minutes.

  When operating in urban canyons and / or very weak signal conditions, GPS course estimates may be unstable and unreliable. A very large noise model must be used. The deselection scheme is used to select out-of-range measurements from the corresponding Kalman filter that are too far from normal values.

  Such a ratio is always estimated when the vehicle 110 goes straight or the net course change cancels out to zero (eg, 15 ° right turn followed by 15 ° left turn). be able to. The ratio compensates for wheel radius differences and straightens the run. If a ratio of 1.0 is applied blindly, dead reckoning propagation can plan a route with a large curve even when actually traveling on a straight road.

Experience has shown that the terms A and A _left and A _right can deviate from reality during a turn, depending on how the suspension of the vehicle 110 operates. In general, more turning energy is observed that gives the impression of oversteering (ie, ground tracking shows more than a true course change).

  To compensate for this effect, a speed compensation parameter “C” is introduced here to further compensate for the rotational step already compensated by any actual difference in wheel radius. The general form of the C parameter is the value 0: 1. At low speed, the C parameter is near zero and at high speed it converges but does not reach one.

  The C parameter is more difficult to estimate. This is because it requires observation of turning conditions over the entire speed range possible for the vehicle 110. Therefore, a baseline or default model is used. The C parameter is frequently improved with another single state Kalman filter over the life of the vehicle 110.

  A typical form of the C parameter is a unit from zero speed to a baseline value called LowSpeedCutOff. The curve then decreases and becomes linear to the maximum speed at which the curve stays flat at a fixed lower value. The slope of the intermediate region is estimated in real time. The independent variable for simplifying the speed representation is the sum of the left and right wheel rotation increments, here called sumTicks.

The modeling formula for estimating the C parameter is
deltaHeading = A * (1 + C * (compST-LowSpeedCutOff)) * compTT
It is.

An estimate of the C parameter can be formed as follows.
C estimate = (deltaHeadingGPS-A * compTT) / (A * compTT * (compST-LowSpeedCutOff))
A baseline estimate of the A parameter is required, and the C parameter has no units.

  The A parameter converts a change in the wheel rotation increment between the left and right wheels into a course change. The course change is then integrated with an arbitrary constant to produce a total dead reckoning course. The computation of the A parameter requires collecting at least two GPS speed estimates that can obtain a delta course, and collecting compensated rotational step estimates corresponding to the same integration period. Therefore,

A-estimate = deltaHeadingGPS / (compTT * C)
It is. Here, the A estimate (A-estimate) is radians per rotation increment.

  Experiments show that the accuracy depends on the quality of the GPS course measurements. Software programming should have at least two ways to estimate the course. For example, the least square batch estimator estimates the east and north velocities from a set of GPS Doppler measurements obtained in one time interval, so it does not have a dynamic model and is therefore delayed under dynamics. Does not have. In another example, the estimator uses a navigational Kalman filter with a complex measurement error model for each GPS Doppler measurement and a complex model of how GPS speed and position change from epoch to epoch. I have. Under weak signal conditions with higher noise ratios, the Kalman filter provides less variability in east and north velocities.

  Another single state Kalman filter is used to blend together the time series of A estimates. Each A estimated value has a measurement error model based on an error model in the GPS course component. A processing noise model is included that sets a filter time constant that slowly adapts to changing tire conditions.

  The A estimate depends on two other parameters, the wheel radius ratio r, and the speed compensation model C. The A parameter is estimated continuously from the initial actual behavior and uses one value for the ratio and default model until the parameters can be estimated respectively.

In estimating parameter B, delta range parameter B is used to set the speed for dead reckoning. It converts the sum of left and right wheel rotation increments to dead reckoning speed. Parameter B is estimated using the GPS speed and the compensated total step measurement (compST) as follows:
B-estimate = GPS speed in one second / compST in one second
The B estimate is blended with a single state Kalman filter, where the measurement noise is a function of the GPS speed error estimate. The processing noise for the Kalman filter sets a time constant for how B varies with time. In general, tires compress and expand at various speeds and vehicle loads. Accordingly, the amount of processing noise to be included is set to have a time constant of about 5 minutes.

For the course offset O parameter, it is necessary to have an absolute course estimate from dead reckoning to estimate the change in dead reckoning position from a set of new left and right wheel rotation increments. This parameter is called DR_heading here.
DR_heading = heading offset + sum of all delta-headings

The course offset is set first when the first reliable GPS course becomes available (eg, as soon as the GPS receiver moves at a speed of several meters per second or more). To initialize
Heading offset = Heading from last fix
It is.

And to update
DR heading on first update = heading offset + deltaHEading1
It is. In the second update,
DR heading = heading offset + deltaHeading1 + deltaHeading2;
= heading offset + sum of all DR deltaHeadings;
= heading offset + sumDeltaHeading
It is.

If the sum of all such delta course estimates is complete, the course offset is a fixed constant and does not need to be updated. In practice, however, the heading offset may change fairly rapidly due to system noise and modeling failure. In order to continuously estimate the course offset in order to keep the course offset accurate, another signal state Kalman filter is required.
The heading offset estimate, O = GPS heading-sumDeltaHeading

  Then, it is blended with all the course offset estimated values corresponding to the measurement noise model based on the GPS course error estimated value. The time constant is set at about 5 minutes.

In summary, calibration proceeds as follows in Table VII.

  One embodiment of the present invention comprises a tightly coupled GPS and dead reckoning software application program for execution as a GPS application in a host computer. It is connected to receive measurements from a GPS measurement platform (MP) on a vehicle with wheels. For example, MP 704 (FIG. 7) on vehicle 110 (FIG. 1) with wheels 112, 114, 116, and 118. The tightly coupled GPS and dead reckoning software application program includes input processing for collecting time, fix triggers, Doppler, and pseudorange reports from the GPS measurement platform. The offset calculation process from GPS time to host computer time is used to align otherwise asynchronous data generated by the vehicle to GPS time. Least square snapshot estimates include position (P), velocity (V), calibration parameters for wheel radius and ratio (B), delta course and delta range (D), and individual new position fix and GPS system time Is calculated for the time based on The Kalman filter is included and configured for position (P), velocity (V), calibration parameters for wheel radius and ratio (B), delta course and delta range (D), and time, and Process and propagate dead reckoning delta range, delta heading, combined mode.

The continuous mode selection process selects operation in GPS only mode, dead reckoning navigation only mode, or a combined mode of both GPS and dead reckoning, depending on the availability of GPS solutions and wheel data calibration. The new fix computation process computes hardware pre-data and adjusts the GPS millisecond timer connected to the time offset computation process. The buffer processor collects time stamped CANbus data for wheel rotation ticks measured by the vehicle wheel transducer. Kalman filter dead reckoning calibration, A _L and A _R calibration parameters for delta-heading / tick difference between the left and right wheels, as well as, B _L and B _R Calibration for delta-range / tick of the left and right wheels Process the parameters as well as the course offset calibration parameters to translate the total delta course to a known course reference. Dead Reckoning Data Processor converts data from the buffer processor to the delta range, delta heading, and delta heading sum information for later processing by a Kalman filter and includes a dead reckoning error model . The application programming interface (API) outputs a new navigation fix.

Tightly coupled GPS and dead reckoning software application program operates in one of three modes including GPS receiver alone, DR computer alone, and combined mode including both GPS receiver and DR computer A selection process may further be included. Operation in the GPS receiver single mode occurs when a GPS fix is available, there are satellite vehicles that are available consistently enough, and more than two satellite vehicles are being tracked. Operation in DR computer single mode occurs when GPS fix is not available or when two or fewer satellite vehicles are being tracked. And operation in combined mode confirms from inspection that no more than two satellite vehicles are being tracked, or that there are no satellite vehicles available consistently, and that calibration is available. It happens when it is done. The new navigation fix is then output through the API.
[feedback]

  Embodiments of the present invention use road mapping to provide positioning feedback. It is assumed that the user's navigation system is moving on a vehicle and that the vehicle is traveling on the road. It is also assumed that this road mapping captures all road information, but it is not always correct due to new construction, repairs and detours. Also, this road mapping database is usually stored on a DVD disc and is typically updated only once a year, but the user does not purchase the latest version for a few years. Therefore, feedback must be adjusted to travel off-road.

  Time and position estimates can be provided as feedback to assist dead reckoning propagation during GPS expiration and outage. In order to make use of the estimated time and position, the feedback process must be initialized and data selection must be made before and during the GPS outage.

  In order to be usefully applied, feedback is made at even intervals (eg, every 5 seconds) or every second. The feedback arrives with a delay of at most 1 GPS epoch after the position is output. Feedback can arrive at any time until the next fix is processed. In practice, this means within 800 milliseconds of the previous output. Any feedback that arrives after 2 GPS epochs is of low value and is therefore discarded.

  In FIG. 10A, the time series 1000 receives feedback within one second after the corresponding fix. For example, fix x, fix x + 1, fix x + 2, fix x + 3, fix x + 4, fix x + 5, fix x + 6, after time, feedback x, feedback x + 1, feedback followed by x + 2, feedback x + 3, feedback x + 4, feedback x + 5, and so on.

  In FIG. 10B, the feedback time series 1050 arrives within 1-2 seconds from the corresponding fix. For example, fix x, fix x + 1. After the time of fix x + 2, fix x + 3, fix x + 4, fix x + 5, and fix x + 6, feedback x-1, feedback x, feedback x + 1, feedback x + 2, This is followed by feedback x + 3 and feedback x + 4.

The format of the feedback message is
PERDAPI, ETPOS, TIME, LAT, N / S, LON, E / W, HEAD, CHKS;
Where PERDAPI is the PERD application programming interface;
ETPOS is an estimated time / position sentence indicator;
TIME is the feedback time;
LAT is the feedback latitude;
N / S is north / south;
LON is the feedback longitude;
E / W is East / West;
HEAD is a feedback course;
CHKS is a checksum.

  FIG. 11 (a), FIG. 11 (b) and FIG. 12 represent a feedback implementation of an embodiment with two parts. The first part 1100 in FIG. 11 (a) and FIG. 11 (b) validates the information and updates the structure. Feedback statements that come in with information from the road mapping are enabled for receipt. The feedback structure is filled and includes both feedback information and the corresponding GPS receiver derived position / velocity / time (implicitly including speed and course). Data in the feedback structure (GPS and feedback information) is analyzed to determine whether it is suitable feedback data for use in DR propagation.

  Specifically, in FIG. 11 (a), as shown in FIG. 10 (a), the incoming feedback statement with information from the road mapping is tested in step 1102 and the feedback follows the fix within 1 second. Check if it is. If not, step 1104 tests to see if feedback follows the fix within 2 seconds, as shown in FIG. 10 (b). If Yes, step 1106 sets a flag indicating that the feedback input data is valid. If No, step 1108 sets a flag indicating that the feedback input data is not valid. Step 1110 sets an appropriate waiting time, computes latitude, longitude, and altitude (LLA) in decimal, fills the structure with feedback information, and fills the structure with related GPS fix information. The initial core library process is used to populate the feedback estimation time and position structure and update the feedback accuracy and validity rating. In the prototype, these two functions are called tpSetDrEtPosition and pfDrEtUpdateConf. The result of that information is used later in DR propagation.

  In FIG. 11 (b), step 1114 propagates the feedback position when the feedback is delayed and satisfies the position feedback estimation time and position structure. Step 1116 determines whether the input data flag has been set valid. If no, step 1118 disables any course adjustment. If yes, step 1120 is between the reference course and the feedback course, between the current feedback course and the previous feedback course, between the current reference (GPS) course and the previous reference course, and Calculate the difference between the position and the feedback position. Feedback and reference (GPS) successive course differences, as well as position and course differences between feedback and reference, are used as appropriate to set the rotation flag, good feedback flag, and bad feedback flag. Qualitatively, similar heading changes from feedback and GPS data and stable position differences should be to allow rotation and good feedback flags. A similar course change or unstable position difference sets a bad feedback flag.

  Step 1122 tests the good feedback flag, and if it is good, step 1124 raises the accuracy rating. Step 1126 tests the bad feedback flag, and if it is bad, step 1128 reduces the accuracy rating. If neither the good or bad feedback flag is raised, the accuracy rating is not affected. Step 1129 checks whether or not the failure feedback of the rotation flag is bad. If not, step 1130 updates the course adjustment. Otherwise, step 1118 disables any course adjustment.

  In FIG. 12, the second portion 1200 is provided for DR propagation. Appropriate estimation time and location structure is determined. Usually it is determined from the previous GPS / DR fix. If feedback is present and passes the aptitude test, the feedback estimation time and position structure is used. Some fixes follow normal DR propagation, and a valid feedback position is the sum of the jump to this position and the DR course followed by normal DR propagation again until the conditions for using the feedback structure are satisfied again. To guide the corrections made.

  The decision is made on which position structure to use for DR propagation, either the feedback position or the normal position from the previous fix. All GPS fixes use normal estimated time and location structures. The range is updated only during DR fix and reset to zero when not operating in DR mode.

  Specifically, step 1202 fetches the feedback location accuracy rating and updates the range since the last use of the feedback. Step 1204 determines whether the mileage since the last use of the feedback is sufficient, whether the position feedback has the lowest accuracy rating, whether the feedback position is not too old, and whether there is a course correction enabled Confirm whether or not. If all are confirmed, step 1208 corrects the DR course total by adjustment, and step 1210 uses the feedback estimation time and position structure for DR propagation. If not, step 1206 uses the normal estimated time and position structure for DR propagation.

  “A turn in progress” is defined as a change in the feedback course of more than 8 degrees or a change of the reference course of more than 8 degrees. Bad feedback is when the feedback and reference course exceeds the bad course limit and the turn is in progress, or the feedback and reference position is greater than 35m and the position uncertainty (posSigma) is less than 35m Or when the feedback and reference positions are separated by more than 50 m. Good feedback is defined as being in GPS mode, where the feedback and reference positions are separated by less than 20 meters, and the feedback and reference courses differ by less than 5 degrees. The bad course limit is 10 degrees plus 12% of course change (with 180 degrees as the upper limit). Bad feedback is not declared by course errors up to 32 degrees for very large turns. The maximum position accuracy rating is 12, and the rating threshold for its use is 6. The position and course are not updated more than once per 100 m in the DR trajectory.

［アルゴリズム］
Ｃ１を推定するためのモデル式は、
dh = A * (1 + C1 * (SumT - LowSpeedCutOff)) * dT
である。並べ替えると、
C1 = (dh - A * dT) / (A * dT * (SumT - LowSpeedCutOff))
である。ここで、
TL：左車輪刻み（Left wheel ticks）
TR：右車輪刻み（Right wheel ticks）
A：デルタ針路を演算するためのパラメータ
Ratio：「Ratio = TL / TR」の数式に対して推定される左右の車輪刻みの比
SumT：車輪刻みの合計は、「SumT = TL + TR」として定義される
dT：車輪刻みの差は、「dT = (TL - TR) + (1 - Ratio) / (1 + Ratio) * SumT」として定義される。 In summary, Table VIII describes parameters for wheel ticks in a CAN frame, and Table IX lists the speed compensation parameters set by the API.

[algorithm]
The model equation for estimating C1 is
dh = A * (1 + C1 * (SumT-LowSpeedCutOff)) * dT
It is. Once sorted,
C1 = (dh-A * dT) / (A * dT * (SumT-LowSpeedCutOff))
It is. here,
TL: Left wheel ticks
TR: Right wheel ticks
A: Parameters for calculating the delta course
Ratio: Ratio of left and right wheel increments estimated for the formula "Ratio = TL / TR"
SumT: Sum of wheel increments is defined as “SumT = TL + TR”
dT: Wheel tick difference is defined as “dT = (TL−TR) + (1−Ratio) / (1 + Ratio) * SumT”.

  FIG. 13 represents a server-based roadmap feedback system for the tightly coupled GPS and dead reckoning vehicle navigation embodiment of the present invention, referred to herein by the general reference numeral 1300. Server-based system 1300 includes at least one network server 1302 that can wirelessly communicate with at least one vehicle 1304 through wireless network 1306. The GPS navigation satellites 1308 are normally visible from the vehicle 1304, but may experience signal impairments caused by being in a parking lot, tunnel, etc. Wireless network 1306 includes, for example, conventional GSM mobile phone technology with dial-up wireless transceiver phones 1310 and 1312. Wireless transceiver telephone 1312 may experience signal impairments common to cellular telephone services.

  The roadmap database 1320 is accessible by a feedback server 1322 on a network (eg, the Internet). Such a roadmap database 1320 can include a map database service sold by Navtech, Inc. (Chicago, Illinois), etc., and is the latest public, private, accessible to subscriber-operated vehicles 1304. Display safe and safe road information. Subscriber authentication unit 1324 restricts real-time access to feedback server 1322 to authorized subscribers.

  If the vehicle 1304 does not enjoy the benefits provided by its roadmap software and display, the network server 1302 can be configured as shown in FIGS. 1, 3, 10, 11 (a), 11 (b), and FIG. As described above with reference to FIG. 12, the minimum map information required for feedback correction can be provided. The feedback allows GPS and dead reckoning mixed positions to be drift compensated each time the snap error exceeds a predetermined value. Without such feedback, the scope of map snapping is exceeded. The feedback used here corrects the position by integrating the previous drift correction and keeps the snapping range at a reasonable level. The ultimate goal is to always output a more accurate vehicle position.

  Limited immediate local area map information is downloaded from the roadmap database 1320 through the wireless network 1306 to the local prefetch database 1330. Since communication between the wireless network 1306 and the mobile wireless transceiver 1312 is frequent and in some cases increases signal impairment, the local look-ahead database 1330 is sufficient to continue a reasonable time and distance feedback operation. It is necessary to have the correct data. For example, a 5 minute vehicle movement at a local speed limit.

  The bandwidth capabilities of the wireless network 1306 and mobile wireless transceiver 1312 are severely limited, so the map information communicated and stored in the local look-ahead database 1330 eliminates all data that is not essential for feedback correction jobs. Should. Thus, the transmitted data is reduced to a simple vehicle position restriction consisting of intersecting line segments with no name or different color. Most road segments can be described by straight line segments having start and end coordinates.

  As described above, the dead-reckoning vehicle range and course solution are computed by dead reckoning unit 1332 with wheel sensor 1334. The GPS navigation position and velocity solution is provided by a GPS navigation receiver 1336 with an antenna 1338 that receives signals from GPS satellites 1308. Blending unit 1340 controls the interaction between dead reckoning unit 1332 and GPS navigation receiver 1336 as described above. In addition, it constrains the blend solution to match the results to the road segment data provided by the local look-ahead database 1330. Blending unit 1340 provides feedback and calibration to dead reckoning unit 1332 and GPS navigation receiver 1336 and also provides data for viewing navigation solutions and display 1342.

  While particular embodiments of the present invention have been described and illustrated, it is not intended to limit the invention. Modifications and changes will no doubt become apparent to those skilled in the art, and it is intended that the invention be limited only by the scope of the appended claims.

100-GPS and dead reckoning combination, 102-display, 104-GPS receiver, 106-antenna, 108-dead reckoning (DR) computer

Claims (10)

A GPS receiver mounted on a vehicle and subject to signal transmission obstacles from navigation satellites in orbit,
A DR computer coupled to the GPS receiver and providing range and course information computed by dead reckoning (DR) during the signal failure, wherein vehicle navigation solutions and assistance are through a screen display to the user Being continuously available,
A wheel notch sensor coupled to a DR computer and providing rotation data relating to rotation of individual wheels supporting the vehicle;
In a car navigation system comprising a road map database having road segment information matching the car navigation system,
A network server that provides road segment information from the roadmap database for limited areas requested by powered vehicles;
An estimate of the true radius of the individual wheels,
The estimate of the true radius of the individual wheels is the range change (ie, delta range) and course change (ie, delta course), the wheel step sensor from the wheel increment sensor to generate information about the operation of the vehicle. Combined with rotation data,
As a vehicle navigation solution, dead reckoning results are sometimes output alone, and absolute position information periodically obtained from the GPS receiver is propagated by the DR computer with delta range and delta course information,
Road segment information stored in the look-ahead database matches the vehicle navigation solution and is used to correct drift in dead reckoning propagation during GPS outage;
The GPS and dead reckoning mixed position is corrected for drift whenever the snapping error exceeds a predetermined value,
The vehicle navigation solution and assistance is continuously available through a screen display to the user, and periodically drifts from the road segment alone from the GPS receiver, alone by the DR computer, or by feedback correction. Derived from the composite provided by the GPS receiver and the DR computer, modified to
The map matching function is a car navigation system based on map segments provided by the server.   A computer program further comprising: selecting and deriving the vehicle navigation solution from the GPS receiver alone, from a DR computer alone, or from a composite provided by both the GPS receiver and the DR computer. Item 1. The car navigation system according to Item 1. A computer program that operates in one of three modes, including a GPS receiver alone, a DR computer alone, and a combined mode that includes both the GPS receiver and the DR computer;
Operation in the GPS receiver single mode occurs when a GPS fix is available, there is a satellite vehicle that is available sufficiently consistently, and more than two satellite vehicles are being tracked,
Operation in the DR computer single mode occurs when GPS fix is not available, or when two or fewer satellite vehicles are being tracked and calibration is available,
Operation in the combined mode has been verified from inspection that no more than two satellite vehicles are being tracked, or that there are no satellite vehicles available consistently, and that calibration is available. The car navigation system according to claim 1, which occurs in some cases. A programmable permanent stop bit;
A branch of the conditional program that immediately follows the start of the GPS measurement hardware, the conditional branch depends on the status of the programmable permanent stop bit, calibration is available, and When the programmable permanent stop bit is true, transfer control to the DR computer single mode, or if the programmable permanent stop bit is chaotic, a GPS fix is available 4. The car navigation system according to claim 3, further comprising: transferring control to the GPS single mode.   Further comprising automatic processing for continuous calibration of an estimate for each true radius of each of the individual wheels, the absolute position information periodically obtained from the GPS receiver provided by a wheel step sensor. The car navigation system according to claim 1, wherein the car navigation system is compared with the rotation data. A buffer and time stamp process for receiving a wheel rotation data packet received from a controller area network (CAN);
The car navigation system according to claim 1, further comprising a dead reckoning Kalman filter for estimating and calibrating the wheel step rotation data from the buffer and time stamp processing.   Further comprising an initialization value that is computed to approximate the true radius of each of the individual wheels and is used to provide an estimate of the delta range, delta course, and delta course total for the dead reckoning solution The car navigation system according to claim 1.   The car navigation system according to claim 1, further comprising speed effect compensation for adjusting an estimated value of the wheel radius. Tightly coupled GPS, dead reckoning navigation, and map matching navigation software application running as a GPS application in a host computer and connected to receive measurements from a GPS measurement platform (MP) on a wheeled vehicle A program,
Input processing to collect time, fix trigger, Doppler, and pseudo-range reports from a GPS measurement platform (MP) device mounted on a vehicle with wheels;
An offset calculation process from GPS time to host computer time, which is generated by the vehicle and aligns asynchronous data without GPS,
Position (P) based on each new position fix and GPS system time, velocity (V), calibration parameters for wheel radius and ratio (B), delta course and delta range (D), and least squares snap to time A shot estimator;
Configured for position (P), velocity (V), calibration parameters for wheel radius and ratio (B), delta course and delta range (D), and time, dead reckoning delta range, delta course, combined mode And a Kalman filter to handle propagation,
Depending on the availability of GPS solutions and wheel data calibration, continuous mode selection process operating in GPS only mode, dead reckoning alone mode, or a combination of both GPS and dead reckoning modes;
A new fix calculation process that calculates hardware pre-data and adjusts a GPS millisecond timer connected to the time offset calculation process;
A buffer process for collecting time-stamped CANbus data relating to wheel rotation ticks measured by a vehicle wheel transducer;
_{A L} and _{A R} calibration parameters for delta course / tick difference between the left and right wheels, and _{B L} and _{B R} calibration parameters for DeltaRange / tick of the left and right wheels, as well as heading the total delta course known Dead reckoning calibration Kalman filter that processes the course offset calibration parameter that translates to the reference,
Dead reckoning data processing including dead reckoning error model, converting the data from the buffer processing into delta range, delta course, and delta course total information for later processing by the Kalman filter;
Feedback position data processing in which drift is corrected each time the GPS and dead reckoning mixed position exceeds a predetermined value,
Road segment matching process for correcting drift in dead reckoning propagation during GPS outage with road segment information periodically downloaded from a network server to a local look-ahead database;
An application program comprising an application programming interface (API) that outputs a new navigation fix. A mode selection program that operates in one of three modes, including a GPS receiver alone, a DR computer alone, and a combined mode that includes both the GPS receiver and the DR computer;
Operation in the GPS receiver single mode occurs when a GPS fix is available, there is a satellite vehicle that is available sufficiently consistently, and more than two satellite vehicles are being tracked,
Operation in the DR computer single mode occurs when GPS fix is not available, or when two or fewer satellite vehicles are being tracked and calibration is available,
Operation in the combined mode has been verified from inspection that no more than two satellite vehicles are being tracked, or that there are no satellite vehicles available consistently, and that calibration is available. Occurs when
10. The tightly coupled GPS and dead reckoning software application program of claim 9, wherein a new navigation fix is subsequently output through the API.

Images