Doppler-based cellular navigation system

Abstract

A vehicle having a Doppler-based cellular navigation system is provided. The vehicle includes a radio frequency (RF) antenna, an RF receiver in communication with the RF antenna, a memory, and a controller. The memory includes a land-based RF transmitter database having land-based RF transmitter location information. The controller is in communication with the RF receiver and the memory. The controller is configured to monitor a Doppler shift in an RF signal received from the land-based RF transmitter. The controller is further configured to determine location information when the controller detects that the Doppler shift is zero in the received RF signal. The controller is further configured to implement the determined location information while navigating the vehicle.

Description

Background Art

[0001] A kind of navigation system currently used is the Global Navigation Satellite System (GNSS). GNSS determines position information using satellite signals sent from multiple satellites, which are received at the receiver of the vehicle. According to each satellite signal, the distance to the satellite that sent the signal is determined. A common way to determine the distance is by sending clock and satellite position information in the associated signal. Using multiple distance determinations, the positioning system of the vehicle can determine the position of the vehicle. GNSS generally provides high-precision position and time information worldwide. However, there are some limitations in the current GNSS. These limitations include multipath signals (especially when operating in an urban environment), sunspots and solar flares that may potentially interfere with satellite signals or even damage satellites, interference / deception of satellite signals, deliberate degradation or confusion, and satellite failures that may cause intermittent coverage when relocating spare satellites. Therefore, it is desirable to have another navigation system that is available when GNSS is damaged.

[0002] Another common type of navigation system used is an inertial navigation system (INS). An INS provides relative measurements given an initial reference. Relative measurements can be used to determine position, orientation, and velocity information. However, relative measurements are subject to drift errors over time. Therefore, it is desirable to have a complementary system that can correct for drift errors in the relative measurements of an INS.

[0003] For the reasons stated above and other reasons stated below which will become apparent to those skilled in the art upon reading and understanding the present specification, there is a need in the art for an effective and efficient navigation system that can supplement another type of navigation system when needed. Summary of the invention

[0004] The following summary of the invention is made by way of example and not by way of limitation. The purpose of providing the summary of the invention is merely to help the reader understand some aspects of the subject matter. The embodiment provides a Doppler-based cellular navigation system to generate position information. The position information can be used for navigation of a vehicle. In addition, in one example, when position information from other navigation systems is not available, the position information from the Doppler-based cellular navigation system can be used, or can be used to supplement the position information from other navigation systems.

[0005] In one embodiment, a vehicle having a Doppler-based cellular navigation system is provided. The vehicle includes a radio frequency (RF) antenna, an RF receiver in communication with the RF antenna, a memory, and a controller. The memory includes a land-based RF transmitter database having location information of land-based RF transmitters. The controller communicates with the RF receiver and the memory. The controller is configured to monitor Doppler shift in the RF signal received from the land-based RF transmitter. The controller is also configured to determine the location information when the controller detects that the Doppler shift is zero in the received RF signal. The controller is also configured to implement the determined location information when navigating the vehicle.

[0006] In another embodiment, a method for determining the position of a vehicle using a Doppler-based cellular navigation system is provided. The method includes identifying a land-based radio frequency (RF) transmitter on a path of travel of the vehicle using a land-based radio frequency (RF) transmitter database; monitoring a Doppler shift in a signal received from the identified land-based RF transmitter as the vehicle continues in the path of travel; determining a closest position of the vehicle to the land-based RF transmitter when the Doppler shift reaches zero; and determining the position of the vehicle based at least in part on the determined closest position to the land-based RF transmitter.

[0007] In yet another embodiment, a method for determining a position of a vehicle using a Doppler-based cellular navigation system includes: monitoring radio frequency (RF) signals using an RF receiver; identifying discrete frequency bands used by the detected RF signals; identifying a land-based RF transmitter based on the identified discrete frequency bands; obtaining land-based RF transmitter information about the identified land-based RF transmitter from a land-based RF transmitter database; monitoring Doppler shift in the detected RF signal; and determining position information of the vehicle at least relative to the identified land-based RF transmitter based at least on the obtained land-based RF transmitter information and when the monitored Doppler shift reaches zero. BRIEF DESCRIPTION OF THE DRAWINGS

[0008] The present invention may be more readily understood and further advantages and uses of the present invention will become more apparent when considered in light of the detailed description and the following drawings, in which:

[0009] Figure 1 is an illustration of a vehicle with a Doppler cellular navigation system traveling along a travel path including satellite and cellular coverage areas according to an exemplary aspect;

[0010] Figure 2 is a block diagram of a vehicle including a position determination system according to an exemplary aspect;

[0011] Figure 3A is a graph of power versus distance for radio frequency signals used in cellular communications;

[0012] Figure 3B Two different vehicle travel paths are shown, which will be Figure 3A Similar power-versus-distance results are provided in the Power-versus-Distance graph of ;

[0013] Figure 4 A vehicle is shown travelling within a transmission zone (coverage area) provided by a land-based RF transmitter;

[0014] Figure 5A Three potential travel paths of a vehicle relative to a land-based RF transmitter are shown;

[0015] Figure 5B Shown with Figure 5A A graph of Doppler shift predictions associated with three potential travel paths for a ground-based RF transmitter;

[0016] Fig. 6A The vehicle angle relative to the ground-based RF transmitter is shown;

[0017] Figure 6B shows the vehicle angle relative to a ground-based RF transmitter applied in 3D space;

[0018] Figure 7 Identifying a possible location of a vehicle using RF signals from a ground-based RF transmitter is shown;

[0019] Figure 8 shows an angular distance plot for calculating angular distance relative to a terrestrial RF transmitter according to an exemplary aspect; and

[0020] Fig. 9 is a flow chart illustrating a method of determining location information using Doppler shift according to an exemplary aspect.

[0021] As is common practice, the various features described are not necessarily drawn to scale, but rather are used to emphasize specific features relevant to the present invention. Reference characters denote similar elements throughout the drawings and text. DETAILED DESCRIPTION

[0022] In the following specific embodiments, reference is made to the accompanying drawings, which form a part of the specific embodiments, and in these drawings, specific embodiments that can implement the present invention are shown by way of illustration. These embodiments are described in sufficient detail to enable those skilled in the art to implement the present invention, and it should be understood that other embodiments can be utilized and can be changed without departing from the spirit and scope of the present invention. Therefore, the following specific embodiments are not restrictive, and the scope of the present invention is limited only by the claims and their equivalents.

[0023] Embodiments of the present invention provide a Doppler-based cellular navigation system. A vehicle can use its own Doppler-based navigation system for location information when location information is not available from other navigation systems, or to supplement the location information of other navigation systems. The Doppler-based cellular navigation system is not inhibited by disabling another navigation system such as GNSS. Further embodiments provide a Doppler-based cellular navigation system that is not limited to multiple users, can be used as a backup, requires a minimal amount of dedicated infrastructure (ground infrastructure is already available), and can operate in all weather conditions.

[0024] A wireless signal, such as a radio frequency (RF) signal used in a cellular communication network, is emitted from a point source that decays as the inverse of the square when observing the signal in the far field. Near-field antenna designs can provide significant signal gain relative to a dipole (omnidirectional antenna). In applications such as mobile base stations that include land-based RF transmitters, antenna designs can be more directional, which is one reason why land-based RF transmitters include antennas arranged in a circular array. Antennas used on land-based RF transmitters can have a transmission range of 120 degrees (or less, such as 15 antennas per tower) depending on design and performance characteristics. In addition, these antennas can be angled so that a certain percentage of the transmitted energy does not exceed the horizontal plane where the antenna is installed (most cellular mobile users are on the ground and below the local antenna plane). Fortunately, due to the diffraction, reflection and antenna transmission characteristics of the signal, part of the signal reaches above the horizontal plane and reaches a large distance. For example, they can reach 45 miles or more. Although the maximum distance in general practice can theoretically be 45 miles, this distance can be reduced to minimize interference with other nearby towers. The spread of global mobile technology provides a potentially useful source of technical data. Examples of useful information that can be obtained from mobile technology by monitoring RF signals include, but are not limited to, aircraft airspeed, signal strength, cellular frequency band channels, and locations of fixed, ground-based RF transmitters.

[0025] See also Figure 1 , shows a vehicle 100 (in this example, an aircraft) configured to determine navigation information including the vehicle's location based at least in part on satellite signals from satellites 102-1 through 102-n and radio frequency (RF) signals radiated from antennas on ground-based RF transmitters 104-1 through 104-n. The ground-based RF transmitters 104-1 through 104-n may be mounted on cellular towers or attached to other fixed locations. Figure 2 A block diagram of components of a vehicle 100 is shown that includes, at least in part, a position determination system 200 for determining position information for navigation. In this example, the vehicle's positioning system 200 includes a controller 202 and a memory 210.

[0026] Generally, the controller 202 may include any one or more of a processor, a microprocessor, a digital signal processor (DSP), an application specific integrated circuit (ASIC), a field programmable gate array (FPGA), or an equivalent discrete or integrated logic circuit. In some example embodiments, the controller 202 may include multiple components, such as any combination of one or more microprocessors, one or more controllers, one or more DSPs, one or more ASICs, one or more FPGAs, and other discrete or integrated logic circuits. The functions attributed to the controller 202 herein may be embodied as software, firmware, hardware, or any combination thereof. The controller 202 may be a part of a system controller or a component controller. The memory 210 may include computer-readable operating instructions that provide positioning functions when executed by the controller 202. Such positioning functions may include the functions of the Doppler-based cellular navigation system 201 described below. The computer-readable instructions may be encoded in the memory 210. Memory 210 is a suitable non-transitory storage medium, including any volatile, nonvolatile, magnetic, optical, or electrical medium, such as, but not limited to, random access memory (RAM), read-only memory (ROM), nonvolatile RAM (NVRAM), electrically erasable programmable ROM (EEPROM), flash memory, or any other storage medium.

[0027] The vehicle position determination system 200 also includes a global navigation satellite system (GNSS) receiver 208 and an associated GNSS antenna 203, an inertial navigation system (INS) 206, and an RF receiver 204 with an associated RF antenna 205. The GNSS receiver is configured to receive satellite signals from the satellites 102-1 to 102-n via the GNSS antenna 203 and determine distance information to each associated satellite 102-1 to 102-n. The distance information is used to determine the position information of the vehicle 100. The controller 202 communicates with the GNSS receiver 208.

[0028] The INS 206 is also in communication with the memory 202. The INS 206 provides relative measurements given an initial reference. The controller 202 can use the relative measurements to determine the position, orientation, and speed of the vehicle 100. However, these relative measurements can accumulate drift errors over time.

[0029] The Doppler-based cellular navigation system 201 includes at least an RF receiver 204, a controller 202, and a memory 210. In other examples, the Doppler-based cellular navigation system 201 includes all of the components in the position determination system 200. The RF receiver 204 is further in communication with the memory 202. The RF receiver 204 receives RF signals from the ground-based RF transmitters 104-1 to 104-n via the RF antenna 205 and transmits the received RF signals to the controller 202. If the RF receiver 204 has sufficient sensitivity, the frequency offset (i.e., Doppler shift) can be detected. As described in detail below, the controller 202 uses the Doppler shift in determining the position information.

[0030] The memory 210 may include a land-based RF transmitter database 212. The land-based RF transmitter database 212 may include identification and location information associated with the land-based RF transmitters 104-1 to 104-n. The controller 202 uses the identification and location information of the land-based RF transmitters 104-1 to 104-n in determining the location information of the vehicle 100. In one embodiment, the controller 202 is configured to add land-based RF transmitter information that is not already in the land-based RF transmitter database 212 (when the land-based RF transmitter information is detected), which can then be transmitted to a remote location that compiles the land-based RF transmitter database 212 and distributes the land-based RF transmitter database 212 to other vehicles.

[0031] In this example, the controller 202 of the position determination system 200 is also in communication with the communication system 214 and the vehicle control system 216. The communication system 214 can be used to transmit the determined position information of the vehicle 100 and the detected ground-based RF transmitters 104-1 to 104-n to a remote location. In one example, the vehicle control system 216 is used to at least partially control the operation of the vehicle 100 including the direction of travel. In addition, in one example, the controller 202 controls the operation of the vehicle control system 216 based at least in part on the determined position information.

[0032] In one example, when satellite signals from satellites 102-1 to 102-n are unavailable (in a non-satellite signal coverage period) or inaccurate for navigation, controller 202 uses position information derived from signals from ground-based RF transmitters 104-1 to 104-n. In other embodiments, controller 202 supplements position information determined using one of satellite signals and inertial signals from INS 206 with position information determined by received RF signals from ground-based RF transmitters 104-1 to 104-n. In yet another embodiment, signals from ground-based RF transmitters 104-1 to 104-n are used to determine position information for vehicle 100. The Doppler-based cellular navigation system 201 described herein may be applied to any type of mobile vehicle, including but not limited to any type of aircraft, including unmanned aerial vehicles, and any land- and water-based vehicles.

[0033] according to FIG. 3A to FIG. 8 Further describing the use of RF signals from the land-based RF transmitters 104-1 to 104-n to find location information. Measurement of the signal strength (RSSI) of the RF signal can provide a relative distance measurement to the land-based RF transmitter. Therefore, the vehicle 100 that detects the RF signal generated by the transmitter and transmitted by the antenna at the land-based RF transmitter can determine the relative distance to the land-based RF transmitter.

[0034] Embodiments of RF receiver 204 monitor RF signals used in cellular wireless bands, such as those used in Global System for Mobile Communications (GSM), Code Division Multiple Access (CDMA), and Long Term Evolution (LTE) wireless technologies. As the relative distance to a land-based RF transmitter (generally referenced by 104) decreases, the measured signal strength increases. This Figure 3A As the vehicle 100 moves closer to the ground-based RF transmitter 104, the signal power 302 increases until it reaches its maximum power strength (which is the closest distance 303 of the vehicle to the ground-based RF transmitter 104). As the vehicle 100 moves away from the ground-based RF transmitter 104, the signal strength decreases, as also shown in FIG. Figure 3A The power versus distance graph 300 is shown.

[0035] However, the distance information to the ground-based RF transmitter derived from the detected signal strength is generally not sufficient to resolve any useful location information. Figure 3BAs shown in , based solely on the strength information, you cannot distinguish between different vehicle paths 304 and 306 associated with the land-based RF transmitter 104, as both of them will provide similar signal strength readings. In addition, the distance information is only related to the specific land-based RF transmitter that transmitted the RF signal. In addition, different land-based RF transmitters may have different power outputs, so the distance may scale differently depending on the RF signals from different land-based RF transmitters.

[0036] See also Figure 4 , the signal strength may provide a probability area 402 within the transmission area 400 (coverage area) of the ground-based RF transmitter 104. Although the probability area 402 provides a data point, the data point is not sufficient to definitively locate an aircraft or other vehicle relative to the ground-based RF transmitter 104. However, the data point may operate similarly to an automatic direction finder (ADF) antenna found on some conventional aircraft and used for navigation purposes. The signal strength measurement essentially provides the slant distance to the ground-based RF transmitter, which may be on a radio tower. This provides a useful value for determining the relative distance to the ground-based RF transmitter.

[0037] Embodiments use the Doppler shift in the receiver RF signal from the ground-based RF transmitter 104 in determining location information. The Doppler shift is the change in the observed frequency of a signal when one of the source of the signal or the observer of the signal moves relative to the other of the source or the observer. Generally, as the observer approaches the source, the signal waves emitted by the source propagating toward the observer are observed to be compressed, which causes the observed frequency to increase, while the signal waves observed by the observer propagating away from the signal source are observed to be stretched, which causes the observed frequency to decrease.

[0038] The measurement of Doppler shift is critical for relatively moving targets because the Doppler shift is proportional to the angle and speed at which the target is moving toward it. The Doppler shift is given by the following formula f d =(2vcosθ / λ). Therefore, the Doppler frequency shift f d It is equal to twice the object (vehicle) moving speed v multiplied by the relative approach angle of the object to the signal transmitter divided by the frequency λ of the transmitted signal. Therefore, the Doppler shift changes based on the relative approach angle to the transmitter (emitter).

[0039] Figure 5A A first travel path 502 of the vehicle 100 , a second travel path 504 of the vehicle 100 , and a third travel path 506 of the vehicle 100 relative to the ground-based RF transmitter 104 are shown. Figure 5BCalculated Doppler shifts associated with a first travel path 502, a second travel path 504, and a third travel path 506 are shown. The first travel path 502 is coaxial with the ground-based RF transmitter 104 and results in Figure 5B 5. In this example, the second travel path 504 is 1 km off-axis and provides a second Doppler shift prediction 524, and the third travel path 506 is 2 km off-axis and results in a third Doppler shift 526. Figure 5A and Figure 5B As shown, as the reference frame (the path of travel of vehicle 100) travels off-axis, the Doppler shift changes. As the off-axis distance to the receiver changes, the perceived Doppler shift is smoother the farther away, and more "squished" together the closer.

[0040] The velocity used to determine in the example can provide north / south (N / S) and east / west (E / W) velocity vectors. For example, in avionics applications, an inertial reference system (IRS) and / or a flight management system (FMS) may be used to provide velocity vectors. The velocity vectors may be combined using simple arithmetic.

[0041] The embodiment uses a cellular ground station to locate the position of a vehicle. A cellular ground station is generally referred to herein as a land-based RF transmitter 104, which includes one or more antennas to radiate RF signals. Several different methods can be used in the example to determine the position using the radiated RF signal. The method requires the movement of the vehicle relative to the land-based RF transmitter 104. The first method involves using a single land-based RF transmitter and using the frequency to determine the position line and using the rate of change of the Doppler shift to measure the distance to the land-based RF transmitter. This option is a simpler specific implementation, but only provides intermittent updates, where inertial navigation is used between updates. The second example uses multiple land-based RF transmitters 104. In this example, the distance and / or azimuth to the land-based RF transmitter is determined, and the intersection of the distance and / or azimuth is used to determine the vehicle position. Multiple land-based RF transmitter 104 examples provide more frequent updates, but will result in a more complex receiver with the ability to simultaneously monitor multiple frequencies from different land-based RF transmitters.

[0042] In a first example using one land-based RF transmitter, as the vehicle 100 travels past the land-based RF transmitter 104, the receive frequency at the vehicle 100 will change from being greater than the transmit frequency at the land-based RF transmitter 104 to being less than the transmit frequency at the land-based RF transmitter 104 due to the Doppler effect. Given a reasonably accurate ground track or even heading from the aircraft's inertial system, in the avionics example, when the receive frequency at the vehicle 100 is equal to the transmit frequency from the land-based RF transmitter 104 (zero Doppler shift at this point), the position of the land-based RF transmitter relative to the aircraft will be at a position perpendicular to the vehicle's path of travel. At this perpendicular point, the vehicle 100 is closest to the land-based RF transmitter 104 that is transmitting the RF signal. As the vehicle passes the land-based RF transmitter 104, the rate of change of the receive frequency will be proportional to the distance from the land-based RF transmitter. This isolates the possible positions into two positions, one on either side of the ground station. Inertial information from an inertial system (such as the INS 206 described above) can then be used to determine which of these is correct. Because this approach only obtains position updates when a ground-based RF transmitter passes by, it will be necessary to use an inertial system to provide navigation between position updates. In the avionics example, the range measurement would be a slant range that includes not only the lateral displacement but also the altitude of the aircraft. The theoretical range estimate accuracy could be on the order of about 10 wavelengths. At cellular frequencies, this would be on the order of about 10 feet.

[0043] Since the Doppler shift is proportional to the relative velocity and angle to the ground-based RF transmitter 104 (base station), it is possible to derive or infer Fig. 6A The vehicle relative angle θ of the ground-based RF transmitter 104 is shown. This can be done knowing the expected frequency band and channel in the RF signal being received. According to the International Telecommunication Union (ITU) and the European Telecommunications Standards Institute (ETSI), the channel must operate at a fixed frequency. The flight speed V of the aircraft in the known avionics example a In this case, the relative angle θ can be determined using the following basic formula:

[0044]

[0045] like Fig. 6A As shown, the above applications of Doppler shift are discussed in a two-dimensional (2D) plane. Determining Doppler shift in 2D can be applied to vehicles that are at low vertical separations relative to the ground-based RF transmitter 104 or that are traversing terrain. However, for aircraft flying at very high altitudes relative to the ground-based RF transmitter 104, Doppler shift analysis can be applied in three-dimensional (3D) space. Applications in 3D Figure 6B606 is shown in . When applied in 3D space, additional considerations need to be taken into account, such as the horizontal plane of the velocity vector components 602 and 604 are driven by the inertial system. In order to obtain the true velocity in 3D space, a combination of the NS, EW and vertical velocity components 606 needs to be combined. This information may already be available in the avionics system of the aircraft. This information can be collected from the bus from digital data communications between avionics systems using communication standards such as Aeronautical Radio Corporation (ARINC) 429. The resulting basic formula from 2D space can still be applied, but now the angle theta (θ) provided is at a "tilt" angle and therefore needs to be solved.

[0046] In an embodiment, the RF receiver 204 is designed to receive a wideband of applicable signals. In one example, the controller 202 uses the RF receiver 204 to track and monitor a specific channel based on the operating instructions stored in the memory 210. Channels in similar signal strength patterns can be considered to be co-located and on the same land-based RF transmitter. In one example, the controller 202 is configured to determine the best three available non-co-located signals based on the operating instructions. The approximate location of the land-based RF transmitter is known and identifiable. In one example, this is to utilize the information in the land-based RF transmitter database 212. The land-based RF transmitter database 212 can include identification and location information related to the land-based RF transmitters 104-1 to 104-n. The identification of the land-based RF transmitter 104 can be carried out from the frequency band in which it broadcasts its RF signal.

[0047] In one example, the location of the vehicle 100 may be determined by the controller 202 through triangulation. Furthermore, with the additional knowledge of the Doppler shift, the location may be determined using only two known ground-based RF transmitters 104. Figure 7 An example of this is shown. Figure 7Two possible locations of the vehicle 100 at positions 702 and 702' at the intersection of the signal coverage area 704 of the land-based RF transmitter 104-1 and the signal coverage area 706 of the land-based RF transmitter 104-2 using triangulation at known signal strengths are shown. To determine the correct position 702 or 702, the embodiment uses Doppler shift analysis as described above. At position 702, the closest distance to the land-based RF transmitter 104-1 is indicated by the first direction indicator 703-1, and the closest distance to the land-based RF transmitter 104-2 is indicated by the second direction indicator 703-2. The closest distance of the vehicle 100 to the land-based RF transmitter indicates the direction in which the RF signal radiated from the antenna of the land-based RF transmitter travels to reach the antenna of the vehicle 100. The direction of travel of the vehicle 100 is further shown by the first vector 705. As shown, the vehicle 100 is at position 702 facing the second land-based RF transmitter 104-2 in the direction close to the first vector 705, at which time the RF receiver 204 will measure the frequency of acceleration from the RF signal from the second land-based RF transmitter 104-2. Another RF receiver 204 of the vehicle 100 at position 702 is at its closest point to the land-based RF transmitter 104-1. At this time, the Doppler shift will change from the frequency of acceleration to the frequency of slowing down relative to the RF signal transmitted from the first land-based RF transmitter 104-1.

[0048] The vehicle 100 at position 702' has not yet reached its closest point to the second land-based RF transmitter 104-2, so the RF receiver 204 is now measuring the frequency of acceleration from the RF signal generated by the second land-based RF transmitter 104-2. At this time, the vehicle 100 at another RF receiver 204 at position 702' has passed its closest point to the land-based RF transmitter 104-1. At this time, the Doppler shift will be measured at the RF receiver 204 at a slower frequency based on the RF signal transmitted from the first land-based RF transmitter 104-1. Based on the Doppler shift information, the controller 102 can determine which position 702 or 702' the vehicle is actually located at.

[0049] In an embodiment, the position determination is repeated with two known land-based RF transmitters to create a derived position table for the vehicle 100. In another embodiment, the positions of the determined land-based RF transmitters are collected and stored in a database 212 that can be disseminated to other vehicles.

[0050] For general positioning determination in avionics applications, relative distances to ground-based RF transmitters and relative orientation are determined. With these values, it is possible to derive the relative position of the aircraft. In one example, the calculated distance is converted into a horizontal distance. This can be done using the approximate location of the cellular tower, the known ground height associated with the ground-based RF transmitter 104 (from the database 212), and the altitude information of the vehicle 100. With this information, the vertical component can be calculated, and with the vertical component, the horizontal component can be determined. Therefore, the calculated distance to the ground-based RF transmitter 104 will result in the distance and orientation from the ground-based RF transmitter 104 to the vehicle 100. In addition, in avionics applications, in the case where the aircraft is not flying straight and level and there are horizontal and vertical components for the Doppler shift, the relative vertical angle from the ground-based RF transmitter 104 to the vehicle 100 can be used to provide a horizontal orientation.

[0051] As described above, the RF cellular communication signals from the cellular base station are used because the land-based RF transmitters operate in discrete frequency bands with multiple discrete channels per frequency band. Examples of frequency bands include 698MHz-806MHz (700MHz band), 806MHz-849MHz / 851MHz-896MHz (800MHz band), 1850MHz-1910MHz / 1930MHz-1990MHz (PCS band), 1710MHz-1755MHz / 2110MHz-2155MHz (AWS band). Across these frequency bands, channels may operate with different bandwidths depending on the signal-to-noise ratio (SNR) from the mobile device to the base station of the cellular network provider. For example, channels 12 and 13 may be included in the 700MHz band. In this example, the effective Doppler shift in this frequency range is approximately 652Hz. With an RF receiver such as a software defined radio (SDR) receiver, it is feasible to be able to track and collect enough data points to be able to resolve the individual channels and their respective Doppler shifts.

[0052] In cases where the Doppler shift is minimal relative to the observed frequency range, it may be necessary to collect a large amount of data and perform appropriate statistical models to provide relatively accurate position data. For example, the angular distance relative to a ground-based RF transmitter can be calculated using Figure 8 Angular distance graph 800 shown in FIG. Angular distance graph 800 provides some position uncertainty information, but with enough data, the expected distribution of angles is Gaussian. One example uses a + / - 1 sigma value for distribution. The more data points used, the better the accuracy of the measurement.

[0053] See also Fig. 9, a method for determining position information using Doppler shift is shown in flowchart 900. Flowchart 900 is provided as a series of sequential blocks. However, in other examples, the sequence can occur in a different order or even in parallel. Therefore, the present invention is not limited to the sequence of blocks listed in flowchart 900.

[0054] At block 902, the vehicle 100 monitors for RF signals transmitted from a land-based RF transmitter. In one example, the controller 202 monitors for RF signals detected by the RF receiver 204. Additionally, in one example, the nearest land-based RF transmitter is monitored. At block 904, a determination is made as to whether an RF signal has been detected. If an RF signal has not been detected at block 904, the process continues to monitor for RF signals at block 902. If an RF signal is detected at block 904, a discrete frequency band of the detected RF signal is identified at block 906.

[0055] At block 908, it is determined whether a ground-based RF transmitter is known based at least in part on the discrete frequency band. In one example, this is accomplished by the controller 202 accessing the database 212 to see if the detected discrete frequency band is associated with a stored ground-based RF transmitter within the area of ​​travel. In one example, if an association with a ground-based RF transmitter is known, information about the ground-based RF transmitter is collected from the database 212 at block 912. The location information may include the location of the ground-based RF transmitter and, if on a cellular tower, the altitude of the ground-based RF transmitter.

[0056] At block 914, the Doppler shift of the received RF signal is monitored. At block 916, it is determined whether the Doppler shift has reached zero. If the Doppler shift has not reached zero at block 916, the process continues to monitor the Doppler shift at block 914. Once the Doppler shift reaches zero, as described above, position information associated with the vehicle and the land-based RF transmitter 104 is determined at block 918. As described above, if there is more than one RF signal from more than one land-based RF transmitter, more position information about the location of the vehicle 100 will be able to be determined. Still other systems such as GPS and INS may be used to determine position information.

[0057] If it is determined that the ground-based RF transmitter 104 is unknown, the collected location information about the detected ground-based RF transmitter 104 may be stored in the ground-based RF transmitter database 212. This information may include location information determined by Doppler shift and / or location information determined from other navigation systems of the vehicle, such as GPS and INS, and discrete frequencies used by the ground-based RF transmitter database 212. The discovered ground-based RF transmitter location information and associated discrete frequencies may be distributed (or shared) to a remote location at block 924. This information may then be collected and distributed to users using a Doppler-based cellular navigation system.

[0058] At block 920, the position determined by the Doppler-based cellular navigation system 201 of the vehicle 100 is then implemented. As described above, it can be used as a standalone system in the navigation of the vehicle 100, or it can be used to supplement another navigation system such as GPS or INS. An example of supplementing another navigation system is to help correct for drift in the INS and provide position information when not enough GPS satellite signals are received at the GNSS receiver 208. The process continues at block 902 to monitor the RF signal.

[0059] As described in the example embodiments above, in the example, Doppler measurements are combined with data from INS 206 to calculate the navigation position. In an alternative embodiment, an inverse may be performed, wherein data from the Doppler sensor is used to correct the navigation position generated by INS 206. As described above, inertial navigation systems are subject to drift errors that accumulate over time. Doppler position measurements can be used to estimate and correct drift errors in INS 206. For example, many inertial navigation systems are implemented using Kalman filters to calculate their positions. Measurements from Doppler-based cellular navigation systems can be used as input to position error estimates in the Kalman filter of INS 206, and thereby correct the inherent drift of the Doppler-based cellular navigation system position solution. The basic method of determining Doppler position using cellular RF signals will remain unchanged in this alternative example embodiment.

[0060] Example Implementation

[0061] Embodiment 1 includes a Doppler-based cellular navigation system. The system includes a radio frequency (RF) antenna, an RF receiver in communication with the RF antenna, a memory, and a controller. The memory includes a land-based RF transmitter database having location information of land-based RF transmitters. The controller communicates with the RF receiver and the memory. The controller is configured to monitor Doppler shift in RF signals received from the land-based RF transmitter. The controller is also configured to determine location information associated with a vehicle when the controller detects that the Doppler shift in the received RF signal is zero. The controller is also configured to implement the determined location information in a navigation vehicle.

[0062] Embodiment 2 includes the system of embodiment 1, wherein the controller is configured to determine location information associated with the vehicle by identifying discrete frequency bands associated with received RF signals and looking up location information of land-based RF transmitters associated with the discrete frequency bands in a land-based RF transmitter database.

[0063] Embodiment 3 includes the system of any of embodiments 1 to 2, further comprising at least one other navigation system. The controller is configured to supplement the position information from the at least one other navigation system with the determined position information from the Doppler-based cellular navigation system.

[0064] Embodiment 4 includes the system of embodiment 3, wherein the at least one other navigation system is a global navigation satellite system (GNSS), and position information determined by the Doppler based cellular navigation system is used during periods of no satellite signal coverage.

[0065] Embodiment 5 includes the system of embodiment 4, wherein the GNSS includes a GNSS receiver in communication with the GNSS antenna. The controller is in communication with the GNSS receiver.

[0066] Embodiment 6 includes the system of embodiment 3, wherein the at least one other navigation system is an inertial navigation system (INS), and the position information determined by the Doppler-based cellular navigation system is used to correct drift in the INS measurements.

[0067] Embodiment 7 includes the system of any one of embodiments 1 to 6, further comprising a communication system in communication with the controller. The controller is configured to cause the communication system to transmit location information of the detected ground-based RF transmitter to a remote location.

[0068] Embodiment 8 includes the system of embodiment 7, wherein the transmitted location information includes at least a frequency of an RF signal generated by the detected ground-based RF transmitter and a location of the detected ground-based RF transmitter.

[0069] Embodiment 9 includes the system of any one of embodiments 1 to 8, further comprising a vehicle control system in communication with the controller. The vehicle control system is configured to control navigation of the vehicle based at least in part on the determined position information when the controller detects a Doppler shift of zero in the received RF signal.

[0070] Embodiment 10 includes a method for determining the position of a vehicle using a Doppler-based cellular navigation system. The method includes identifying a land-based radio frequency (RF) transmitter on a path of travel of the vehicle using a land-based radio frequency (RF) transmitter database; monitoring a Doppler shift in a signal received from the identified land-based RF transmitter as the vehicle continues in the path of travel; determining a closest position of the vehicle to the land-based RF transmitter when the Doppler shift reaches zero; and determining the position of the vehicle based at least in part on the determined closest position to the land-based RF transmitter.

[0071] Embodiment 11 includes the method of embodiment 10, further comprising increasing the determined position accuracy of the vehicle by measuring signals received from a plurality of ground-based RF transmitters.

[0072] Embodiment 12 includes the method of any one of Embodiments 10-11, wherein the ground-based RF transmitter is part of a cellular base station.

[0073] Embodiment 13 includes the method of any one of Embodiments 10 to 12, further comprising determining the inertially determined position of the vehicle at least in part using an inertial navigation system.

[0074] Embodiment 14 includes the method of embodiment 13, further comprising correcting drift in the inertial navigation system based at least in part on monitoring Doppler shift.

[0075] Embodiment 15 includes the method of any one of embodiments 10 to 14, wherein the position of the vehicle is determined by at least one of determining signal strength, determining a relative angle to a ground-based RF transmitter, and using a rate of change of Doppler shift.

[0076] Embodiment 16 includes a method according to any one of embodiments 10 to 15, the method also comprising collecting ground-based RF transmitter information of the vehicle as the vehicle traverses the travel path, the ground-based RF transmitter information comprising at least the frequency of the signal used by the ground-based RF transmitter and the location of the ground-based RF transmitter; and generating a ground-based RF transmitter database at least in part using the collected ground-based RF transmitter information.

[0077] Embodiment 17 includes the method according to embodiment 16, which further includes: sharing the collected ground-based RF transmitter information; generating a ground-based RF transmitter database at a remote location based at least in part on the shared collected ground-based RF transmitter information; and disseminating the ground-based RF transmitter database to other vehicles.

[0078] Embodiment 18 includes a method for determining the position of a vehicle using a Doppler-based cellular navigation system, the method comprising: monitoring a radio frequency (RF) signal using a radio frequency (RF) receiver; identifying a discrete frequency band used by the detected RF signal; identifying a land-based RF transmitter based on the identified discrete frequency band; obtaining land-based RF transmitter information about the identified land-based RF transmitter from a land-based RF transmitter database; monitoring a Doppler shift in the detected RF signal; and determining the position information of the vehicle at least relative to the identified land-based RF transmitter based at least on the obtained land-based RF transmitter information and when the monitored Doppler shift reaches zero.

[0079] Embodiment 19 includes the method according to embodiment 18, and the method also includes supplementing at least one navigation system based on the determined location information.

[0080] Embodiment 20 includes the method of any one of Embodiments 18-19, further comprising: increasing the accuracy of the determined position information of the vehicle by monitoring Doppler shift in a plurality of RF signals from a plurality of ground-based RF transmitters.

[0081] Although specific embodiments have been illustrated and described herein, one of ordinary skill in the art will recognize that any arrangement calculated to achieve the same purpose may be substituted for the specific embodiments shown. This application is intended to cover any modifications or variations of the present invention. Therefore, it is apparent that the present invention is limited only by the claims and their equivalents.

Claims

1. A Doppler-based cellular navigation system (201), the system (201) comprising: Radio frequency (RF) antenna; (204) an RF receiver (204) in communication with the RF antenna (204); a memory (210) comprising a ground-based RF transmitter database (212) having location information of ground-based RF transmitters; and A controller (202) is in communication with the RF receiver (204) and the memory (210), the controller (202) being configured to monitor Doppler shift in an RF signal received from a ground-based RF transmitter (104), the controller (2020) being further configured to determine position information when the controller (2020) detects that the Doppler shift in the received RF signal is zero, and the controller (202) being further configured to implement the determined position information in a navigation vehicle (100).

2. A method for determining the position of a vehicle (100) using a Doppler-based cellular navigation system (201), the method comprising: identifying the nearest land-based radio frequency (RF) transmitter (104) in the travel path of the vehicle (100) using a land-based radio frequency (RF) transmitter database (212); As the vehicle (100) continues in the path of travel, monitoring a Doppler shift in a signal received from the identified nearest ground-based RF transmitter (104); When the Doppler shift reaches zero, determining the closest position of the vehicle to the closest land-based RF transmitter (100); as well as The location of the vehicle (100) is determined based at least in part on the determined closest location to the nearest land-based RF transmitter (104).

3. A method for determining the position of a vehicle (100) using a Doppler-based cellular navigation system (201), the method comprising: monitoring a radio frequency (RF) signal with an RF receiver (204); identifying discrete frequency bands used by detected RF signals; identifying a ground-based RF transmitter based on the identified discrete frequency bands (104); obtaining ground-based RF transmitter information about the identified ground-based RF transmitter (104) from a ground-based RF transmitter database (212); monitoring a Doppler shift in the detected RF signal; as well as Based at least on the obtained land-based RF transmitter information and when the monitored Doppler shift reaches zero, position information of the vehicle (100) at least relative to the identified land-based RF transmitter (104) is determined.

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