Pedal navigation using leo signals and body-mounted sensors

Abstract

A navigation system includes a navigation radio and sensor mountable to a pedal subject. The navigation radio processes RF signals to derive successive range observables for one or more overhead assets such as low-earth orbit (LEO) satellites. A sensor is operable to generate output useful in computing successive positional dead reckoning (PDR) data under pedal motion. The radio includes navigation code operable to obtain a navigation solution including an absolute position solution and one or more of a velocity solution, time solution, and attitude solution based on the successive range observables, ephemerides for the corresponding LEO satellite, and the generated successive PDR data. A PDR component including pedal motion constraints is corrected by occasional LEO satellite ranging data to generate a highly-accurate pedal navigation solution in environments where GPS fails, such as in buildings, shopping malls, dense forests, deep open-pit mines, urban canyons, or in jammed signal environments.

1 . A pedal navigation method comprising:
 generating successive positional dead reckoning data including at least one of position data, velocity data, acceleration data, angular rate data, rotational angle data, and attitude data based on output from one or more sensors generated during pedal motion;   receiving, from one or more LEO satellites, RF signals at an RF antenna coupled to a navigation radio;   obtaining satellite ephemerides for the one or more LEO satellites;   deriving successive range observables for the one or more LEO satellites, based on the received RF signals;   computing a navigation solution including an absolute position solution based on the generated successive positional dead reckoning data, the derived successive range observables, and the obtained ephemerides.   
     
     
         2 . The navigation method of  claim 1 , wherein computing the navigation solution comprises computing a dead reckoning solution based on the generated successive positional dead reckoning data and correcting positional dead reckoning errors using the derived successive LEO satellite range observables. 
     
     
         3 . The navigation method of  claim 2 , wherein computing the dead reckoning solution includes employing one or more of the following motion constraints:
 that a foot is substantially stationary during contact with the ground;   that a foot is substantially non-rotating during contact with the ground;   that a foot is neither accelerating nor decelerating during contact with the ground;   that a pedal subject is moving on the ground;   that travel is limited to pedal velocities; and   that pedal travel is primarily forward travel.   
     
     
         4 . The navigation method of  claim 3 , wherein one or more of the employed motion constraints is employed as a soft constraint to determine when to omit sensor data collected during pedal motion that violates one or more of the employed motion constraints. 
     
     
         5 . The navigation method of  claim 1 , wherein computing the navigation solution comprises relating the derived successive range observables with state components of a dead reckoning solution calculated using the generated successive positional dead reckoning data. 
     
     
         6 . The navigation method of  claim 1 , further comprising establishing an altitude pseudomeasurement for the navigation radio based on at least one of local terrain data, building schematics and an altimeter measurement and employing the altitude pseudomeasurement in computing the navigation solution. 
     
     
         7 . The navigation method of  claim 1 , further comprising establishing, using a magnetometer, one or more of a heading measurement, latitude measurement, and altitude measurement for the navigation radio and employing the one or more established measurements in computing the navigation solution. 
     
     
         8 . The navigation method of  claim 7 , wherein the one or more established measurements is at least partly established as one or more of:
 a projection of a measured magnetic field in a local tangent plane;   a projection of the measured magnetic field on a local nadir vector; and the strength of a measured magnetic field.   
     
     
         9 . The navigation method of  claim 1 , further comprising initializing the navigation radio with an initial navigation solution prior to generating the successive positional dead reckoning data. 
     
     
         10 . The navigation method of  claim 9 , wherein the initial navigation solution is based on at least one of a satellite signal, pseudolite signal, UAV signal, terrestrial reference station signal, and user-entered location data. 
     
     
         11 . The navigation method of  claim 1 , further comprising determining, using the output from the one or more sensors, when a foot is in contact with the ground. 
     
     
         12 . The navigation method of  claim 11 , wherein generating the successive positional dead reckoning data is based, at least in part, on the determining when a foot is in contact with the ground. 
     
     
         13 . The navigation method of  claim 1 , further comprising correcting sensor bias estimates and gravity subtraction errors accumulated in generating the successive positional dead reckoning data. 
     
     
         14 . The navigation method of  claim 1 , wherein the derived successive range observables include at least one of a pseudorange measurement, carrier phase measurement, and a Carrier Doppler shift frequency measurement. 
     
     
         15 . The navigation method of  claim 14 , wherein the range observables are derived from an iGPS Iridium Advanced Waveform signal. 
     
     
         16 . A pedal navigation system comprising:
 at least one sensor mountable on a pedal subject and operable to generate one or more outputs useful in computing successive dead reckoning data including at least one of position data, velocity data, acceleration data, angular rate data, rotational angle data, and attitude data;   a navigation radio couplable to the sensor, the navigation radio comprising:
 an RF antenna operable to receive RF signals from one or more LEO satellites; 
 an RF front end operable to downconvert and digitize the RF signals; 
 a digital processor operable to derive successive range observables from the downcoverted RF signals for the one or more LEO satellites; 
 a navigation code stored in media and including instructions executable on the digital processor to compute a navigation solution including an absolute position solution based on the computed successive dead reckoning data, the derived successive range observables, and ephemerides for the one or more LEO satellites. 
   
     
     
         17 . The navigation system of  claim 16 , wherein the sensor comprises a six-degrees of freedom inertial measurement unit (IMU) including three orthogonal rate gyros and three orthogonal accelerometers. 
     
     
         18 . The navigation system of  claim 17 , further comprising a three-axis magnetometer substantially fixed relative to a coordinate frame of the IMU and operable to provide at least one of heading data, latitude data, and altitude data to the navigation radio. 
     
     
         19 . A pedal navigation system comprising:
 a navigation radio;   a sensor mounted to a pedal subject and coupled to the navigation radio, the sensor operable to generate one or more outputs useful in computing successive dead reckoning data including at least one of positional data, velocity data, acceleration data, angular rate data, rotational angle data, orientation data, and attitude data;   an RF antenna electrically coupled to the navigation radio and operable to receive RF signals from one or more moving overhead assets;   an RF front end operable to downconvert and digitize the RF signals to produce digital IF signals;   a digital processor operable to compute successive dead reckoning solutions based on the successive dead reckoning data, and to compute successive range observables from the digital IF signals for the one or more moving overhead assets at a frequency substantially corresponding to the computation of the successive dead reckoning solutions and wherein the one or more moving overhead assets is travelling so as to generate appreciable geometric variation in the successive range observables;   a navigation code stored in media and including instructions executable on the digital processor to calculate a navigation solution including an absolute position solution based on the successive dead reckoning solutions and the successive range observables.   
     
     
         20 . The navigation system of  claim 19 , wherein the pedal subject comprises one of a pedestrian, a mounted rider, legged animal and a legged robot. 
     
     
         21 . The navigation system of  claim 19 , wherein the navigation code is configured to employ one or more of the following motion constraints:
 that a foot is substantially stationary during contact with the ground;   that a foot is substantially non-rotating during contact with the ground;   that a foot is neither accelerating nor decelerating during contact with the ground;   that a pedal subject is moving near the ground;   that travel is limited to pedal velocities; and   that pedal travel is primarily forward travel.   
     
     
         22 . The navigation system of  claim 19 , further comprising at least one or more of a magnetometer, altimeter, multi-antenna array, sun sensor, and digital compass coupled to the navigation radio and wherein the navigation code is configured to correct one or more navigation solution states using data generated from outputs of the one or more of a magnetometer, altimeter, multi-antenna array, sun sensor, and digital compass. 
     
     
         23 . The navigation system of  claim 19 , wherein the navigation code is configured to calculate the navigation solution employing an altitude pseudomeasurement based on at least one of terrain map data, building schematic data, an altimeter measurement and user-provided location data. 
     
     
         24 . The navigation system of  claim 19 , wherein the navigation code comprises an extended Kalman filter employing a measurement model, dynamics model and a state vector definition wherein the state vector definition includes a navigation radio position, a navigation radio velocity, a navigation radio clock offset, a sensor rate-gyro bias, a sensor accelerometer bias; and a navigation radio attitude estimate; and wherein the measurement model defines a relationship between the state vector and each of the range observables and sensor measurements. 
     
     
         25 . The navigation system of  claim 19 , wherein the navigation solution further includes at least one of a velocity solution, time solution, and attitude solution. 
     
     
         26 . The navigation system of  claim 19 , further comprising an ultra-stable oscillator. 
     
     
         27 . A pedal navigation method comprising:
 calculating successive positional dead reckoning solutions based on successively sampled positional dead reckoning data including at least one of velocity data, acceleration data, angular rate data, rotational angle data, orientation data, and attitude data based on output from one or more sensors generated during pedal motion;   receiving, at an RF antenna coupled to a navigation radio, RF signals broadcast from one or more overhead assets;   deriving successive range observables for the corresponding one or more overhead assets based on the received RF signals, wherein the one or more overhead assets is travelling so as to generate appreciable geometric variation relative to the RF antenna in the successive range observables; and   computing a navigation solution including an absolute position based on the successive calculated positional dead reckoning solutions and the derived successive range observables.   
     
     
         28 . The pedal navigation method of  claim 27 , further comprising determining from the generated sensor output when a foot has impacted the ground. 
     
     
         29 . The pedal navigation method of  claim 27 , further comprising determining from the generated sensor output a frequency of a repeating pedal motion. 
     
     
         30 . The pedal method of  claim 27 , wherein the navigation solution further includes at least one of a velocity solution, time solution, and attitude solution.