Base station-free RTK GNSS positioning

Abstract

The techniques described herein leverage MCMF capabilities to provide a local RTK solution for mobile devices, in which an initial highly accurate location determination for the mobile device can be leveraged to generate RTK corrections that can be used to make subsequent highly accurate location determinations without requiring measurement information from an RTK base station. The RTK corrections can be applied to GNSS measurements taken by the mobile device over an extended period of time while retaining the ability to provide a highly accurate location determination for the mobile device. Additional corrections can also be obtained and applied to the RTK corrections to extend this period even further.

Description

[Technical Field]

[0001] The present invention relates generally to the field of satellite-based positioning, and more particularly to error correction of Global Navigation Satellite System (GNSS) terms for more accurate position determination. [Background technology]

[0002] High-precision positioning can provide significant value to a variety of modern applications for mobile devices. For example, for autonomous driving applications, it is not only useful to have meter-level positioning to determine which lane of the road a vehicle is located in, but it is even more useful to have sub-meter-level positioning to determine where the vehicle is located within the lane. Consumer-grade GNSS receivers now offer high-quality carrier-phase measurements with multi-constellation, multi-frequency (MCMF) capabilities. Summary of the Invention [Means for solving the problem]

[0003] Real-time kinematic (RTK) corrections can enable global navigation satellite system (GNSS) receivers to provide more accurate positioning. As described in more detail herein, this more accurate positioning is enabled by using carrier-based ranging based on the carriers of GNSS signals, along with measurement information from base stations that enables differential correction of errors from various service sources. The techniques described herein leverage multi-constellation, multi-frequency (MCMF) capabilities to provide a local RTK solution for mobile devices, in which an initial, highly accurate location determination for a mobile device can be leveraged to generate RTK corrections, which can be used to make subsequent, highly accurate location determinations without requiring measurement information from an RTK base station. This RTK correction can be applied to GNSS measurements taken by the mobile device over an extended period of time while retaining the ability to provide a highly accurate location determination for the mobile device. To extend this period of time even longer, additional corrections may be obtained and applied to the RTK corrections. It may further be noted that while the correction techniques described herein are described as “RTK corrections,” embodiments are not so limited. Similar techniques may be employed to employ differential corrections at one or more subsequent locations based on the initial location.

[0004] An exemplary method of RTK positioning of a mobile device according to the present specification includes acquiring a first GNSS measurement at a first time, the first GNSS measurement including an ionospheric-free carrier phase coupling at a first location of the mobile device, and determining a correction term based at least in part on the first GNSS measurement and the first location. The method further includes acquiring a second GNSS measurement at a second time, the second GNSS measurement including an ionospheric-free carrier phase coupling at a second location of the mobile device. The method also includes determining a second location of the mobile device at the second time based at least in part on the second GNSS measurement and the correction term. In one exemplary mobile device, the steps may be performed by a processor (e.g., a digital signal processor or an application processor) within the mobile device. The processor may receive measurements from a GNSS receiver within or otherwise in communication with the mobile device. In other examples, all of the functionality may be incorporated into a GNSS receiver that outputs the determined mobile device location to another component of the mobile device, such as a processor (e.g., a digital signal processor or an application processor), memory, or display.

[0005] An example mobile device according to the present disclosure comprises a memory and one or more processing units communicatively coupled to the memory and communicatively coupled to or configured to execute a GNSS receiver. The one or more processing units are configured to: acquire, via the GNSS receiver, a first GNSS measurement at a first time, the first GNSS measurement including an ionospheric-free carrier phase coupling at a first location of the mobile device; and generate a correction term based at least in part on the first GNSS measurement and the first location. The one or more processing units are additionally configured to acquire, via the GNSS receiver, a second GNSS measurement at a second time, the second GNSS measurement including an ionospheric-free carrier phase coupling at a second location of the mobile device. The one or more processing units are also configured to determine a second location of the mobile device at the second time based at least in part on the second GNSS measurement and the correction term.

[0006] An example device according to the present specification comprises means for obtaining a first GNSS measurement at a first time, the first GNSS measurement including an ionospheric-free carrier phase coupling at a first location of a mobile device, and means for generating a correction term based at least in part on the first GNSS measurement and the first location. The device further comprises means for obtaining a second GNSS measurement at a second time, the second GNSS measurement including an ionospheric-free carrier phase coupling at a second location of the mobile device. The device also comprises means for determining a second location of the mobile device at the second time based at least in part on the second GNSS measurement and the correction term.

[0007] An example non-transitory computer-readable medium according to the present specification has instructions thereon for RTK positioning of a mobile device, the instructions, when executed by one or more processing units, causing the one or more processing units to obtain a first GNSS measurement at a first time, the first GNSS measurement including an ionospheric-free carrier phase coupling at a first location of the mobile device, and generate a correction term based at least in part on the first GNSS measurement and the first location. The instructions, when executed by the one or more processing units, further cause the one or more processing units to obtain a second GNSS measurement at a second time, the second GNSS measurement including an ionospheric-free carrier phase coupling at the second location of the mobile device. The instructions, when executed by the one or more processing units, also cause the one or more processing units to determine a location of the mobile device at the second time based at least in part on the second GNSS measurement and the correction term. [Brief explanation of the drawings]

[0008] [Figure 1] 1 is an illustration of an overhead view of a vehicle traveling through an intersection. [Figure 2] 1 is an illustration of an overhead view of a vehicle traveling through an intersection. [Figure 3] 1 is a simplified diagram of a conventional RTK system using a base station. [Figure 4] 1 is a flowchart of an embodiment of a method for applying RTK GNSS corrections without using an RTK base station. [Figure 5A] 1 is an illustration of a timeline showing when RTK measurement information is received by a rover station from a base station according to a conventional RTK position estimation technique. [Figure 5B] 5B is a timeline illustration similar to FIG. 5A, but showing how RTK correction intervals can be significantly extended using embodiments provided herein. [Figure 6]1 is a graph of simulated results in which the position error relative to the initial position (at time 0) is plotted over time. [Figure 7] 1 is a flow diagram of a method for RTK positioning of a mobile device, according to one embodiment. [Figure 8] FIG. 2 is a block diagram of various hardware and software components of a rover station, according to one embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0009] According to some example implementations, like reference symbols in various drawings indicate like elements. Additionally, multiple instances of an element may be indicated by the first digit of that element followed by a letter or hyphen and a second digit. For example, multiple instances of element 110 may be indicated as 110-1, 110-2, 110-3, etc., or as 110a, 110b, 110c, etc. When referring to such an element using only the first digit, any instance of that element should be understood (e.g., element 110 in the previous example would refer to elements 110-1, 110-2, and 110-3 or elements 110a, 110b, and 110c).

[0010] Several exemplary embodiments are now described with reference to the accompanying drawings, which form a part of this specification. Specific embodiments in which one or more aspects of the present disclosure may be implemented are described below, but other embodiments may be used, and various changes may be made without departing from the spirit of the scope of the present disclosure or the appended claims.

[0011] As used herein, the terms "position" and "location" are used interchangeably. Additionally, the terms "position fix," "position fix," "location estimate," and the like are also used interchangeably herein with respect to GNSS-based positioning to refer to the estimated position of a mobile device, rover station, or other device equipped with a GNSS receiver.

[0012] Highly accurate location determination for consumer electronics can be important in a wide variety of applications. Figures 1 and 2 show one such example: autonomous driving.

[0013] FIG. 1 illustrates an overhead view of a vehicle 110 traveling through an intersection 120. In this example, the vehicle 110 travels from a first location 130 to a second location 140 along a travel path 150. However, an estimated travel path 160 using conventional GNSS location determination techniques would place the vehicle 110 in a different lane or even off the road. This is because the accuracy of conventional GNSS position determination can include errors of several meters, which may be insufficient for the needs of autonomous driving. For example, autonomous driving level L2 and above often requires decimeter-level accuracy. Conventional GNSS alone cannot guarantee this level of accuracy. While GNSS can sometimes provide very accurate positions at a given location, it cannot guarantee such accuracy, even for a few seconds, especially when the vehicle is moving. An autonomous vehicle following the travel path 150 within only a short travel distance may have experienced multiple accidents.

[0014] Figure 2 is an overhead view illustration of the same conditions as Figure 1. However, rather than using conventional GNSS as in the example of Figure 1, RTK positioning with GNSS is used, providing real-time high precision positioning that provides an estimated path of travel 170 that is more closely aligned with the actual path of travel 150. As can be seen, RTK positioning can provide position determination within decimeter or even centimeter accuracy, and thus can be used in autonomous driving and other applications.

[0015] RTK positioning is a GNSS-based positioning technique that uses carrier-based ranging by determining the number of carrier cycles between GNSS satellites and a rover station. RTK positioning may involve calculations to remove various errors (e.g., satellite clock and orbit, ionospheric and tropospheric delays, phase windup, solid-earth tides, ocean loading, and / or site displacement including polar tides) through differential corrections made using observations from a highly accurate GNSS receiver at a reference location and assuming the observations have virtually the same errors. As shown in FIG. 3, conventional RTK systems employ one or more “base stations” to determine these differential corrections. However, in conventional RTK, the RTK correction information provided to the rover station (e.g., a mobile device) must be frequently refreshed to maintain accuracy. Traditionally, this refresh rate is typically once per second, rarely once every few seconds or more.

[0016] 3 is a simplified diagram of a conventional RTK system 300. As mentioned, the RTK system 300 enables highly accurate GNSS position fixes for the rover station 310 by using GNSS receivers in both the rover station 310 and the base station 320 that receive RF signals 330 from satellite vehicles (SVs) 340 from one or more GNSS constellations (e.g., Global Positioning System (GPS), Galileo (GAL), Global Navigation Satellite System (GLONASS), Beidou, etc.). As mentioned above, the type of rover station 310 used may vary depending on the application and may include any of various types of mobile devices that can access GNSS positioning data, such as mobile devices equipped with GNSS receivers. Such mobile devices may include, for example, consumer electronics or other mobile consumer devices, such as mobile phones, tablets, laptops, wearable devices, vehicles, etc.

[0017] To perform a conventional GNSS position fix, the rover station 310 can use code-based positioning to determine the range of each of the SVs 340 based on determined delays in the generated pseudo-random binary sequence received in the RF signal 330. The rover station 310 can use ephemeris (or navigation) data for the SVs 340 to more precisely calculate the location of each SV 340 at a particular moment. Using the range and location information for the SVs 340, the rover station 310 can then determine a position fix for that location. This position fix may be determined, for example, by a standalone positioning engine (SPE) executed by one or more processors in the rover station 310. However, the resulting accuracy of the position fix for the rover station 310 is subject to errors caused by the orbit and clock of the SVs 340, ionospheric and tropospheric delays, and other phenomena. As shown in FIG. 1, this can result in an accuracy on the order of a few meters, which may not be desirable for many applications.

[0018] Conventional RTK positioning can provide a high-precision solution by using carrier-based ranging based on the carrier of the RF signal 330 and using the base station 320 to make similar observations from a reference location, which can be used to make differential corrections for errors from various error sources. The base station 320 includes a fixed GNSS receiver that uses the carrier-based ranging and known location to provide RTK measurement information (also known as “RTK service data”). The RTK measurement information is communicated to the rover station 310, for example, via a data communications network 350, and used by the rover station 310 as correction information to reduce errors (e.g., orbit and clock errors, ionospheric delays, tropospheric delays, etc.) as described above by comparing the RTK measurement information with SV 340 measurements made by the rover station 310 to determine a precise position fix for the rover station 310. This position fix may be determined, for example, by a Precise Positioning Engine (PPE) executed by one or more processors in the rover station 310. More specifically, in addition to the information provided to the SPE, the PPE may use RTK measurement information and additional correction information, such as tropospheric and ionospheric, to provide highly accurate carrier-based position fixes. Several GNSS techniques, such as Differential GNSS (DGNSS), Real Time Kinematic (RTK), and PPP, can be employed in the PPE.

[0019] As mentioned, to maintain the accuracy of the position fix for the rover station 310, the rover station 310 may need to frequently receive updated RTK measurement information from the base station 320. For example, RTK measurement information may be provided to the rover station 310 once per second. This can be problematic for at least three reasons. First, at any given time, there may be a large number of rover stations 310 (e.g., tens, hundreds, thousands, or more), and thus the RTK system 300 may consume the bandwidth of the base station 320 for positioning overhead data rather than carrying user data for the data communications network 350. Second, RTK services often require payment each time RTK measurement information is provided to the rover station 310. Thus, obtaining and maintaining a high-precision position fix for the rover station 310 can become costly over time. Third, the rover station 310 loses the ability to make highly accurate RTK position estimates in the event of a data outage that prevents it from providing RTK measurement information to the rover station 310.

[0020] According to embodiments provided herein, RTK measurement information and subsequent differential error corrections can be derived from measurements taken by the rover station 310 itself, rather than by the base station 320. That is, by leveraging measurements taken by the rover station 310 at an initial location (e.g., the first location 130 in FIG. 2 ) where the position fix (which may be based on RTK measurement information from the base station 320) is highly accurate, differential corrections can be applied later to maintain highly accurate position estimates (e.g., the estimated travel path 170) for the rover station 310 over extended periods of time without requiring additional RTK measurement information from the base station 320. Among other benefits, this can significantly reduce network bandwidth and costs. In some embodiments, for example, rather than receiving RTK measurement information every second, the rover station 310 can go 1200 seconds (20 minutes) or more without requiring additional RTK measurement information. Depending on desired functionality, some embodiments may obtain RTK measurements at additional or alternative intervals (e.g., every 10 minutes, 15 minutes, 25 minutes, or 30 minutes). (Additional information on this point is provided herein with respect to Figures 5A and 5B.) In these embodiments, the rover station 310 can effectively generate and use its own RTK corrections, such as by leveraging ionospheric-free carrier phase coupling from measurements taken with an MCMF GNSS receiver.

[0021] 4 is a flowchart of one embodiment of a method for applying RTK GNSS corrections without the use of a base station, the functions of which are described mathematically. The functions in each of the blocks shown in FIG. 4 may be performed by hardware and / or software components of the rover station 310. (Exemplary hardware and software components of the rover station 310 are shown in FIG. 8 and described in more detail below.) It may be noted that while the embodiment shown in FIG. 4 and described below includes certain terms and equations, alternative embodiments may use alternative terms and / or equations.

[0022] In block 410, an initial measurement is taken at a start time, t0. The techniques for high-accuracy location estimation for the rover station 310 provided herein are aided by a highly accurate initial location estimate. Accuracy may be maintained relative to the accuracy of the initial location estimate. Thus, the rover station 310 may perform the functions in block 410 after an accurate initial location estimate is created. This initial location estimate may be based, for example, on RTK positioning data after convergence / ambiguity correction. (Other applications may not require convergence / ambiguity correction if position accuracy after time t0 relative to the position at time t0 is desired, rather than absolute position accuracy.) The rover station 310 need not be static at the start time t0 and may be moving.

[0023] The measurement at the start time (t0) (shown in block 410) can be expressed as: ∇Φ IF,t0 =(∇ρ IF,t0 +∇LOS t0 *dX t0 +(∇Trop IF,t0 +∇MAP t0 *dWet t0 ) +∇dSat t0 +∇N IF,t0 (1) where the variables in the formula are defined as follows: ∇ - single difference operator between satellites Φ IF - Ionosphere-free carrier phase coupling (e.g., from a combination of GPS L1, L2, and L5 carriers, GAL E1, E5A, E5B, and E6 carriers, and / or BDS B1I, B1C, B2A, B2B, and B3 carriers) ρ - the calculated geometry extent LOS - Satellite Line of Sight Vector dX - the position error to be estimated Trop - Tropospheric delay calculated using the model MAP - Tropospheric moist component mapping function Wet - The wet tropospheric zenith delay error to be estimated. Sat - satellite orbit and clock composite error N - Inaccuracy term for ionospheric free carrier phase coupling

[0024] In this embodiment, ionospheric errors may not need to be considered in equation (1) because they can be reduced using the ionospheric rejection function of the MCMF GNSS receiver in the rover station 310. More specifically, when GNSS signals pass through the ionosphere, ionospheric refraction occurs. However, the first-order contribution (99.9%) of the error resulting from this refraction is inversely proportional to the square of the signal frequency. Therefore, when at least two signals with different frequencies from the same satellite are available, this first-order contribution is a linear combination of the signals, i.e., the ionospheric-free carrier-phase combination Φ IF These signals can be removed in an MCMF receiver that can detect them by making measurements using ionospheric delays. (Similar ionospheric-free coupling is valid for pseudorange measurements.) In this way, an MCMF GNSS receiver can make measurements of multiple RF signals 330 transmitted on different frequencies that account for ionospheric delays (e.g., GPS L1 and L5 frequencies, GAL E1 and E5A frequencies, BDS B1I and B2A frequencies, etc.). However, alternative embodiments may utilize receivers that do not provide ionosphere-free observations in this regard, and instead account for ionospheric-related errors by estimating the ionospheric delay at a starting time t0 and then estimating the ionospheric delay at time t1.

[0025] In block 420, an RTK correction term corresponding to the start time (t0) is determined. The rover station 310 can derive an RTK correction term for use in maintaining high precision positioning based on the measurements of block 410 at the start time t0. As shown in block 420, the RTK correction term at the start time (t0) can be expressed as: ∇Corr IF,t0 =∇LOS t0 *dX t0 +∇MAP t0 *dWet t0 +∇dSat t0 +∇N IF,t0 (2)

[0026] In block 430, the rover station 310 can then take measurements at the "current time" (ti), which can be expressed as: ∇Φ IF,ti =(∇ρ IF,ti +∇LOS ti *dXti) +(∇Trop IF,ti +∇MAP ti *dWet ti )+∇dSat ti +∇N IF,ti (3)

[0027] The rover station 310 can then apply corrections to the measurements in block 430 by differentiating the terms in equations (2) and (3). The location at the current time, ti, is relative to the location at the start time, t0 (which may occur after convergence / inaccuracy correction), so the same inaccuracy terms can be used in both equations (2) and (3). Thus, ∇N IF,ti =∇N IF,t0 This gives us the following: and ∇dSat ti ≒∇dSat t0 , so that the resulting measurement at the current time ti after the correction has been applied can be expressed as follows, as shown in block 440 of FIG. ∇Φ IF,ti =∇ρ IF,ti+∇LOS ti *(dX ti -dX t0 )+(∇LOS ti -∇LOS t0 )*dX t0 +∇Trop IF,ti +∇MAP ti *(dWet ti -dWet t0 ) +(∇MAP ti -∇MAP t0 )*dWet t0 (4)

[0028] Using this corrected measurement of equation (4), the location of the rover station 310 is estimated by a location / position estimator using GNSS positioning techniques. The location / position estimator may be part of a positioning engine (e.g., PPE) and may use estimation techniques such as by using an extended Kalman filter (EKF), weighted least squares (WLS), a hatch filter, a particle filter, etc. That is, the location / position estimator can be used to estimate the position of the rover station 310 at a current time t i relative to the position of the rover station 310 at a start time t0. (dX ti -dX t0 ) (5)

[0029] In block 450, the rover station 310 determines whether new RTK corrections are needed. If not, the method may proceed to block 460, where time advances (ti = ti + 1), and the operations shown in blocks 430-460 may continue to repeat until it is determined that new RTK corrections are needed, at which point the process includes obtaining a new high-precision position estimate, as shown in block 470. This high-precision position estimate may be used as a new reference point, and the process may begin again at block 410. The determination in block 450 of whether new RTK corrections are needed may be based on any of a variety of factors, which are described in more detail below. According to some embodiments, the frequency at which new measurements and position estimates are made (e.g., how often the functions shown in blocks 430-460 repeat) may match the frequency at which conventional RTK measurement information is retrieved (e.g., once per second). Other embodiments may perform this function more or less frequently, depending on the desired functionality. It may also be noted that embodiments may implement the process shown in FIG. 4 differently. For example, according to some embodiments, measurements taken at a starting time t0 (shown in block 410) may be made to obtain an initial highly accurate position estimate rather than a position estimate taken later.

[0030] By computing its own correction terms, the rover station 310 can maintain high accuracy for long periods of time after convergence (e.g., repeating the functions shown in blocks 430-460) without requiring RTK measurement information from the base station or other means of high-accuracy position estimation (which may be performed in block 470). Figures 5A and 5B are illustrations that help visually convey this concept.

[0031] FIG. 5A is an illustration of a timeline representing the times at which RTK measurement information, such as RTK service data, is received by the rover station 310 from the base station 320 according to a conventional RTK position estimation technique. These times are represented by arrows 510. The time before convergence / inaccuracy correction and the time after convergence / inaccuracy correction are also shown. The boundary between these times represents the time at which the inaccuracy term (e.g., the term N in Equation (1)) is determined. As one skilled in the art will appreciate, determining the inaccuracy term, which represents the carrier phase inaccuracy (an integer), enables carrier-based ranging and results in a high-precision estimate for the rover station 310. That is, the time period after convergence / inaccuracy correction is the time during which a high-precision RTK position estimate is maintained by continuing to receive RTK measurement information from the base station 320. As can be seen, the period at which RTK measurement information is received from the base station 320, labeled the RTK correction interval 520, is the same both before and after convergence. Conventionally, the RTK correction interval 520 is 1 second.

[0032] FIG. 5B is an illustrative timeline similar to FIG. 5A but showing how the RTK correction interval 520 can be significantly extended using embodiments provided herein, such as the method shown in FIG. 4. That is, for embodiments utilizing RTK measurement information received from a base station 320 to determine an initial high-precision position estimate, reception of the RTK measurement information before convergence / inaccuracy correction may proceed normally, with the standard RTK correction interval 520 for determination of the initial position estimate. However, once the initial position estimate is obtained after convergence / inaccuracy correction, additional RTK correction information may not be needed for some time, thereby significantly extending the RTK correction interval 520. In some embodiments, additional RTK measurement information may be received after convergence / inaccuracy correction before increasing the RTK correction interval 520.

[0033] FIG. 6 is a graph of simulated results, for example, plotting position error over time relative to an initial position (at time 0). The simulation, in which the rover station 310 used its own RTK corrections without using RTK measurement information from the base station 320, lasted 1200 seconds (20 minutes). The North error 610 remained below approximately 0.5 dm, the East error 620 remained below 1 dm, and the Up error 630 remained below approximately 1.5 dm. Thus, the accuracy is significantly improved over conventional GNSS (e.g., as shown in FIG. 1 ) and can be equal to or similar to the accuracy provided in a conventional RTK positioning environment using RTK measurement information from a base station in the manner shown in FIG. 5A . Thus, the accuracy is significantly improved over conventional GNSS (e.g., as shown in FIG. 1 ) and can be equal to or similar to the accuracy provided in a conventional RTK positioning environment using RTK measurement information from a base station in the manner shown in FIG. 5A . Thus, the embodiments provided herein can be used in high precision applications such as autonomous driving (e.g., as shown in FIG. 2), but achieve high precision without consuming bandwidth within the limited resources of a base station, and achieve high precision with better resiliency by not relying on base station communications.

[0034] The significant increase in the convergence / inaccuracy-corrected RTK correction interval 520 (e.g., by 1200 times in the example shown in the simulation results of FIG. 6 ) enabled by the embodiments described herein provides various advantages over conventional RTK positioning. The significant reduction in bandwidth can, for example, enable the RTK system 300 to provide RTK measurement information to a much larger number of rover stations 310 using the same or less bandwidth. This can also mean significantly reduced operating costs for the rover stations 310 if payment for RTK measurement information from the base station 320 is required. The technique can also be utilized when there is a data outage in the RTK system 300 that prevents communication of RTK measurement information from the base station 320 to the rover station 310.

[0035] Again, conventional RTK measurement information from the base station 320 may be used to determine an initial high-precision position estimate (as shown in FIG. 5B ), but this initial position estimate need not be an RTK position estimate. That is, the initial position estimate may be generated using techniques in addition to or instead of RTK positioning. For example, precise point positioning (PPP) may be used, which uses a network of global base stations to determine GNSS satellite orbits and clock corrections that provide a high-precision position estimate for the rover station 310.

[0036] In some embodiments, additional corrections may be obtained to extend the post-convergence / inaccuracy-corrected RTK correction interval 520 without the need for a new high-precision position estimate or additional RTK measurements from the base station. That is, with respect to FIG. 4 , a correction may be applied in block 430 (to the corrected measurements of equation (4)) to extend the length of time that the functions of blocks 430-460 can repeat before a new RTK correction is required in block 450.

[0037] For example, one correction that may be used to extend the RTK corrections may be a correction for the orbit clock error, ∇dSat. Over an extended period of time (e.g., a long RTK correction interval 520), an approximation of the orbit clock error (∇dSat ti ≒∇dSat t0) may cause the corrected measurements (Equation (4)) to become inaccurate over time. Therefore, according to some embodiments, the mobile device may extend the RTK correction interval 520 by obtaining orbital clock error corrections from a Space-Based Augmentation System (SBAS) and / or other sources. By extending the RTK correction interval in this manner, embodiments can further reduce the need for RTK measurement information from the base station 320. Similarly, corrections may be made for additional or alternative errors accounted for in the corrected measurements (Equation (4)), which may be provided by other sources, including other rover stations 310 (e.g., via peer-to-peer (P2P) communications), Internet of Things (IoT) devices, cellular devices (e.g., via Long Term Evolution (LTE), Fifth Generation New Radio (5G NR)), etc. Additionally or alternatively, embodiments may further implement inter-satellite single differencing so that further consideration of receiver clocks, GNSS inter- / intra-frequency biases and constellation biases, and / or receiver phase center variation effects is not required. In some embodiments, the rover station 310 may have settings that allow a user or application to extend the RTK correction interval 520 using these types of error correction techniques.

[0038] Returning to the function of block 450 of FIG. 4, the determination of whether new RTK corrections are needed may be made using any of a variety of techniques. In some embodiments, a timer may be set so that the correction interval 520 does not exceed a certain amount of time. In some embodiments, this may be based on whether additional correction information is received, accuracy requirements, and / or other factors. For example, the orbit clock error (∇dSat) may be assumed to increase by a certain amount over a certain period of time. Thus, given the accuracy requirements of a particular application, embodiments may determine whether new RTK corrections are needed based on a threshold amount of time. If the accuracy requirements for a given application require the rover station 310's position estimate to be accurate to within 15 cm and the orbit clock error is assumed to increase by a maximum of 5 cm every 5 minutes, it may be determined (at block 450 of FIG. 4) that new RTK corrections are needed if 15 minutes have passed since the initial position estimate.

[0039] Additionally or alternatively, the determination of whether new RTK corrections are needed may be based on whether the position error estimate exceeds a certain threshold. The Horizontal Estimated Position Error (HEPE) is an accuracy value generated, for example, by the positioning engine of the rover station 310. Thus, some embodiments may determine (at block 450 of FIG. 4) that new RTK corrections are needed if the HEPE value exceeds a certain accuracy threshold. Again, this value may be application dependent. Thus, for example, if an application requires accuracy of less than 20 cm, new RTK corrections may be obtained if the HEPE value is 20 cm or greater.

[0040] Additionally or alternatively, embodiments may employ other factors in determining whether new RTK corrections are needed. Environmental factors may be considered. For example, a high-traffic environment in an autonomous vehicle application may require higher accuracy than, for example, a low-traffic environment. Additionally or alternatively, the availability and / or accuracy of other sensors may be considered. For example, if an autonomous vehicle's camera or LIDAR is damaged or unavailable, higher accuracy may be needed. Thus, time and / or accuracy thresholds may be reduced to help ensure that new RTK corrections are acquired in a manner that maintains highly accurate RTK position estimates.

[0041] FIG. 7 is a flow diagram of a method 700 of RTK positioning of a mobile device according to one embodiment. Method 700 may utilize the techniques described above and thus may be considered one implementation of the previously described process shown in FIG. 4. Alternative embodiments may differ in functionality by combining, separating, or otherwise varying the functions described in the blocks shown in FIG. 7. Here, the mobile device may comprise a rover station 310 as used in the above-described embodiment. Thus, means for performing the functions of one or more of the blocks shown in FIG. 7 may comprise hardware and / or software components of the rover station 310, such as the components shown in FIG. 8 and described below.

[0042] In block 710, the function includes obtaining a first GNSS measurement at a first time, the first GNSS measurement including an ionosphere-free carrier phase combination at a first location of the mobile device. As described above, the ionosphere-free carrier phase combination may be obtained using a combination of two or more frequencies, including (but not limited to) GPS L1, L2, and L5 carriers, GAL E1, E5A, E5B, and E6 carriers, and / or BDS B1I, B1C, B2A, B2B, and B3 carriers. Additionally, as shown in the example of equation (1), this first measurement may include various variables that can be used to generate correction terms. As stated, subsequent location determinations are relative to this initial location. Accordingly, some embodiments may further include determining a high-precision location determination for this first location. This may include using RTK positioning based on information received from a base station. That is, in some embodiments, the method 700 further includes determining the first location based at least in part on the RTK measurement information received from the base station, although other forms of high precision location determination, such as PPP, may also be used.

[0043] The means for performing the functions in block 710 may include one or more software and / or hardware components of the rover station 310, such as the bus 805, the processing unit 810, the wireless communication interface 830, the memory 860, the GNSS receiver 880, and / or other software and / or hardware components of the rover station 310, as shown in FIG. 8 and described in more detail below.

[0044] In block 720, the function includes determining a correction term based at least in part on the first GNSS measurement and the first location. As previously described with respect to equation (2) and the function in block 420 of FIG. 4, this correction term may include a variable from the ionospheric free carrier phase coupling used for differential correction of a subsequent ionospheric free carrier phase coupling. It may be noted that the correction term may not be explicitly generated. Instead, the correction term may be implicitly generated when at least some portion of the ionospheric free carrier phase coupling taken at a first time is for differential correction of an ionospheric free carrier phase coupling taken at a subsequent time. Referring to FIG. 4 , for example, rather than taking a two-step approach of (1) explicitly generating a correction term in block 420 and (2) applying the correction term to a subsequent measurement in block 430, an embodiment may use the correction term implicitly by taking a one-step approach of applying a measurement taken at a subsequent time ti in a manner that generates and applies the correction term in a single step (combining the functions of blocks 420 and 430).

[0045] The means for performing the functions in block 720 may include one or more software and / or hardware components of the rover station 310, such as the bus 805, the processing unit 810, the memory 860, and / or other software and / or hardware components shown in FIG. 8 and described in more detail below.

[0046] The function in block 730 includes obtaining a second GNSS measurement at a second time, the second GNSS measurement including an ionospheric-free carrier phase coupling at a second location of the mobile device. As one skilled in the art will appreciate, the uncertainty terms, N, can be solved at the first location (e.g., at or before the first time) to determine an accurate location estimate. Once solved, they can enable subsequent accurate location estimates. Thus, in some cases, the ionospheric-free carrier phase couplings for the first GNSS measurement and the second GNSS measurement may have the same uncertainty terms. In other cases, the terms may be similar (e.g., have values ​​within 10%, 20%, or 30%), but not necessarily the same. Solving the uncertainty terms can enable the convergence shown in FIGS. 5A and 5B.

[0047] The means for performing the functions in block 730 may include one or more software and / or hardware components of the rover station 310, such as the bus 805, the processing unit 810, the wireless communication interface 830, the memory 860, the GNSS receiver 880, and / or other software and / or hardware components shown in FIG. 8 and described in more detail below.

[0048] At block 740, the function includes determining a second location of the mobile device at a second time based at least in part on the second GNSS measurement and the correction term. As shown in FIG. 4, this process may involve applying the correction term to the ionosphere-free carrier phase combination of the second GNSS measurement (e.g., as shown in equations (2)-(4) above and the function of block 430) and using a location / position estimator (e.g., an EKF, a WLS, a Hatch filter, or a particle filter) to estimate the location of the mobile device.

[0049] The means for performing the functions in block 740 may include one or more software and / or hardware components of the rover station 310, such as the bus 805, the processing unit 810, the memory 860, and / or other software and / or hardware components shown in FIG. 8 and described in more detail below.

[0050] As mentioned, embodiments may employ additional techniques for obtaining and applying corrections from sources other than an RTK service. For example, in some embodiments, method 700 may further include performing inter-satellite single differencing to obtain one or more corrections for one or more errors related to the receiver clock, GNSS inter- / intra-frequency bias and constellation bias, or receiver phase center variation effects, or any combination thereof. In such cases, generating the correction terms may be further based at least in part on the one or more corrections. Additionally or alternatively, method 700 may further include obtaining correction data from a source that is not an RTK service, where the correction data includes data enabling orbit correction, clock correction, or both (e.g., satellite orbit and clock composite error), and generating the correction terms may be further based at least in part on the correction data. In particular, the correction data may include data indicative of satellite and / or clock changes from a first time (e.g., t0) to a second time (e.g., t i). As previously mentioned, the source that is not an RTK service may include another mobile device, an IoT device, or other device capable of relaying correction data to the mobile device. In some embodiments, the correction data may come from an SBAS service.

[0051] As indicated by the function depicted in block 450 of FIG. 4 , embodiments may further determine whether a new RTK correction is needed before applying the correction term to subsequent measurements. Thus, according to some embodiments, method 700 may further include determining whether a horizontal position estimation error (HEPE) value exceeds a threshold at a third time, and, in response to determining that the HEPE value exceeds the threshold, (1) requesting RTK measurement information from a base station, and (2) determining a location of the mobile device using the RTK measurement information. As previously indicated, embodiments may additionally or alternatively employ similar functionality using a time threshold and / or a distance threshold. That is, according to some embodiments, method 700 may further include determining whether a threshold amount of time has elapsed since the first time, and, in response to determining that the threshold amount of time has elapsed since the first time, (1) requesting RTK measurement information from a base station, and (2) determining a location of the mobile device using the RTK measurement information. Additionally or alternatively, method 700 may further include determining whether the mobile device has moved a threshold distance since the first time, and in response to determining that the mobile device has moved the threshold distance since the first time, (1) requesting RTK measurement information from a base station, and (2) determining a location of the mobile device using the RTK measurement information.

[0052] Further, as indicated by the functional loop represented by blocks 430-460 in Figure 4, the RTK corrections may be iteratively applied to subsequent measurements. Accordingly, some embodiments of method 700 may further include, for each additional time among one or more additional times following the second time, taking a new respective GNSS measurement at each additional time, wherein each new GNSS measurement includes an ionospheric-free carrier phase coupling, and the ionospheric-free carrier phase coupling for the first GNSS measurement and each new GNSS measurement has the same uncertainty term. A location of the mobile device at each additional time may then be determined based at least in part on the new respective GNSS measurement and the RTK correction term.

[0053] As previously mentioned, the use of a correction term as described herein can be beneficial in the event of an outage of RTK measurement data. According to some embodiments, the function may respond to a determination that RTK measurement information is unavailable. This determination may be made, for example, by the mobile device and may be based on an explicit indication of the unavailability of RTK measurement information sent to the mobile device (e.g., an RTK service provider). Additionally or alternatively, the determination may be based on the mobile device failing to receive expected or requested RTK measurement information from the RTK service provider. (Some embodiments may implement a threshold amount of failed attempts / requests before determining the unavailability of RTK measurement information.)

[0054] Depending on the desired functionality, the mobile device may respond to an outage of RTK measurement data in different ways. For example, according to some embodiments, the mobile device may determine a correction term (e.g., perform the function at block 720) in response to determining unavailability of RTK measurement information. In alternative embodiments, the mobile device may maintain an ongoing correction term (e.g., determine a correction term each time the RTK-based location of the mobile device is determined) and utilize the correction term when RTK measurement information is unavailable. Thus, according to these embodiments, method 700 may include determining unavailability of RTK measurement information and, in response to determining unavailability of RTK measurement information, determining to base a determination of a second location of the mobile device at least in part on the correction term. Again, alternative embodiments may not necessarily be limited to RTK measurement information or outages and may perform similar functions in the event of similar data outages.

[0055] FIG. 8 is a block diagram of various hardware and software components of a rover station 310, according to one embodiment. These components may be utilized as described above (e.g., in connection with FIGS. 1-7). For example, the rover station 310 may perform one or more of the actions of the rover station 310 illustrated in FIGS. 4 and 7 and / or the functions of the method 700 illustrated in FIG. 7. Note that FIG. 8 is intended only to provide a generalized illustration of the various components, any or all of which may be utilized as appropriate. As previously mentioned, the rover station 310 may vary in form and function and may ultimately comprise any GNSS-enabled device, including vehicles, commercial and consumer electronic devices, surveying equipment, and the like. Thus, in some instances, the components illustrated by FIG. 8 may be localized in a single physical device and / or distributed among various networked devices that may be disposed in different physical locations (e.g., different locations on a vehicle).

[0056] The rover station 310 is shown comprising hardware elements that may be electrically coupled (or otherwise in communication as appropriate) via a bus 805. The hardware elements may include a processing unit 810, which may include, but is not limited to, one or more general-purpose processors, one or more special-purpose processors (such as digital signal processing (DSP) chips, graphics processing units (GPUs), application-specific integrated circuits (ASICs)), and / or other processing structures or means. As shown in FIG. 8, some embodiments may have a separate digital signal processor (DSP) 820 depending on the desired functionality. Location determination and / or other decisions based on wireless communications may be performed in the processing unit 810 and / or in a wireless communications interface 830 (described below). The rover station 310 may also include one or more input devices 870, which may include, but are not limited to, a keyboard, touchscreen, touchpad, microphone, buttons, dials, switches, etc., and one or more output devices 815, which may include, but are not limited to, a display, light-emitting diodes (LEDs), speakers, etc. As will be appreciated, the types of input device 870 and output device 815 may depend on the type of rover station 310 in which the input device 870 and output device 815 are integrated.

[0057] The rover station 310 may also include a wireless communication interface 830, which may include, but is not limited to, a modem, a network card, an infrared communication device, a wireless communication device, and / or a chipset (such as a Bluetooth® device, an IEEE 802.11 device, an IEEE 802.15.4 device, a Wi-Fi device, a WiMAX™ device, a wide area network (WAN) device, and / or various cellular devices), etc., which may enable the rover station 310 to communicate over the networks described above with respect to FIG. 1. The wireless communication interface 830 may enable data and signaling to be communicated (e.g., sent and received) with the network, for example, via a WAN access point, a cellular base station and / or other access node type, and / or other network components, computer systems, and / or any other electronic devices described herein. Communication may be performed via one or more wireless communication antennas 832 that transmit and / or receive wireless signals 834. Antenna 832 may comprise one or more individual antennas, one or more antenna arrays, or any combination.

[0058] Depending on the desired functionality, the wireless communication interface 830 may comprise a separate transceiver, a separate receiver and transmitter, or any combination of transceivers, transmitters, and / or receivers for communicating with base stations and other terrestrial transceivers, such as wireless devices and access points. The rover station 310 may communicate with different data networks, which may include various network types. For example, a wireless wide area network (WWAN) may be a code division multiple access (CDMA) network, a time division multiple access (TDMA) network, a frequency division multiple access (FDMA) network, an orthogonal frequency division multiple access (OFDMA) network, a single-carrier frequency division multiple access (SC-FDMA) network, a WiMAX™ (IEEE 802.16) network, etc. A CDMA network may implement one or more radio access technologies (RATs), such as CDMA2000, Wideband CDMA (WCDMA), etc. Cdma2000 includes the IS-95 standard, the IS-2000 standard, and / or the IS-856 standard. A TDMA network may implement GSM, Digital Advanced Mobile Phone System (D-AMPS), or some other RAT. An OFDMA network may employ LTE™, LTE™ Advanced, 5G NR, etc. 5G NR, Long Term Evolution (LTE™), LTE Advanced, GSM, and WCDMA are described in documents from the 3rd Generation Partnership Project (3GPP®). Cdma2000® is described in documents from an organization named “3rd Generation Partnership Project 2” (3GPP2). 3GPP® and 3GPP2 documents are publicly available. The wireless local area network (WLAN) may also be an IEEE 802.11x network, and the wireless personal area network (WPAN) may be a Bluetooth network, an IEEE 802.15x, or some other type of network.The techniques described herein may also be used for any combination of WWAN, WLAN, and / or WPAN.

[0059] The rover station 310 may further include sensors 840. The sensors 840 may comprise, but are not limited to, one or more inertial and / or other sensors (e.g., accelerometers, gyroscopes, cameras, magnetometers, altimeters, microphones, proximity sensors, light sensors, barometers, etc.), some of which may, in some cases, be used to complement and / or facilitate the location determinations described herein.

[0060] An embodiment of the rover station 310 may also include a GNSS receiver 880 capable of receiving signals 884 from one or more GNSS satellites (e.g., SV340) as described herein using an antenna 882 (which may be the same as antenna 832). The GNSS receiver 880 can use conventional techniques to extract the position of the rover station 310 from the GNSS SVs (e.g., SV340 in FIG. 3 ) of a GNSS system, such as GPS, GAL, Global Navigation Satellite System (GLONASS), Quasi-Zenith Satellite System (QZSS) over Japan, Indian Regional Navigation Satellite System (IRNSS) over India, or Beidou Navigation Satellite System (BDS) over China. Additionally, the GNSS receiver 880 may be used with various augmentation systems (e.g., SBAS) that may be associated with or otherwise enabled for use with one or more global and / or regional navigation satellite systems, such as, for example, Wide Area Augmentation System (WAAS), European Geostationary Navigation Overlay Service (EGNOS), Multi-Function Satellite Augmentation System (MSAS), and Geo-Augmented Navigation System (GAGAN).

[0061] It may be noted that while the GNSS receiver 880 is shown in FIG. 8 as a separate component having a separate antenna 882, embodiments are not so limited. As used herein, the term “GNSS receiver” may include hardware and / or software components configured to acquire GNSS measurements (measurements from GNSS satellites). Thus, in some embodiments, the GNSS receiver may comprise a measurement engine (as software) executed by one or more processing units, such as the processing unit 810, the DSP 820, and / or a processing unit within the wireless communication interface 830 (e.g., in a modem). The GNSS receiver may also optionally include a positioning engine (e.g., the SPE or PPE mentioned above) that can use the GNSS measurements from the measurement engine to determine the position of the GNSS receiver. The positioning engine may also be executed by one or more processing units, such as the processing unit 810 or the DSP 820. The processing unit that executes the positioning engine may be the same as or different from the processing unit that executes the measurement engine.

[0062] The rover station 310 may further include and / or be in communication with memory 860. Memory 860 may include machine-readable or computer-readable media, which may include, but are not limited to, local and / or network-accessible storage, disk drives, drive arrays, optical storage devices, solid-state storage devices such as random access memory (RAM) and / or read-only memory (ROM) that may be programmable, flash-updateable, etc. Such storage devices may be configured to implement any suitable data store, including, but not limited to, various file systems, database structures, etc.

[0063] The memory 860 of the rover station 310 may also comprise software elements (not shown in FIG. 8 ) including other code, such as an operating system, device drivers, executable libraries, and / or one or more application programs; such software elements may comprise computer programs provided by various embodiments and / or may be designed to implement methods and / or configure systems provided by other embodiments, as described herein. By way of example only, one or more procedures described with respect to the methods described above may be implemented as code and / or instructions in the memory 860 that are executable by the rover station 310 (and / or the processing unit 810 or DSP 820 within the rover station 310). In one aspect, such code and / or instructions can then be used to configure and / or adapt a general-purpose computer (or other device) to perform one or more operations in accordance with the described methods.

[0064] It will be apparent to those skilled in the art that substantial modifications may be made according to particular requirements. For example, customized hardware may be used and / or particular elements may be implemented in hardware, software (including portable software such as applets), or both. Furthermore, connection to other computing devices, such as network input / output devices, may be employed.

[0065] With reference to the accompanying figures, components that may include memory may also include non-transitory machine-readable media. As used herein, the terms "machine-readable medium" and "computer-readable medium" refer to any storage medium that participates in providing data that causes a machine to operate in a specific manner. In the embodiments provided above, various machine-readable media may participate in providing instructions / code to a processing unit and / or other device for execution. Additionally or alternatively, machine-readable media may be used to store and / or transport such instructions / code. In many implementations, computer-readable media are physical and / or tangible storage media. Such media may take many forms, including, but not limited to, non-volatile media, volatile media, and transmission media. Common forms of computer-readable media include, for example, magnetic media and / or optical media, any other physical media with a pattern of holes, RAM, programmable ROM (PROM), erasable PROM (EPROM), FLASH-EPROM, any other memory chip or cartridge, a carrier wave as described below, or any other medium from which instructions and / or code can be read by a computer.

[0066] The methods, systems, and devices described herein are examples. Various embodiments may omit, substitute, or add various procedures or components, as appropriate. For example, features described with respect to some embodiments may be combined in various other embodiments. Different aspects and elements of the embodiments may be combined in a similar manner. Various components of the diagrams provided herein may be embodied in hardware and / or software. Also, technology evolves, and thus many of the elements are examples that do not limit the scope of the disclosure to those specific examples.

[0067] It has proven convenient at times, principally for reasons of common usage, to refer to such signals as bits, information, values, elements, symbols, characters, variables, terms, numbers, numerical values, or the like. It should be understood, however, that all of these or similar terms are to be associated with appropriate physical quantities and are merely convenient labels. Unless otherwise expressly indicated, and as is apparent from the above description, it should be understood that throughout this specification, descriptions utilizing terms such as "processing," "calculating," "computing," "determining," "generating," "ascertaining," "identifying," "associating," "measuring," "performing," and the like refer to the actions or processes of a particular apparatus, such as a special purpose computer or similar special purpose electronic computing device. Thus, in the context of this specification, a special purpose computer or similar special purpose electronic computing device or system is capable of manipulating or transforming signals that are commonly represented as physical electronic, electrical, or magnetic quantities within the memory, registers, or other information storage, transmission, or display devices of the special purpose computer or similar special purpose electronic computing device or system.

[0068] The terms "and" and "or" as used herein may include a variety of meanings that are expected to depend, at least in part, on the context in which such terms are used. In general, when "or" is used to associate a list, such as A, B, or C, it is intended to mean A, B, and C, which are used herein in an inclusive sense, as well as A, B, or C, which are used herein in an exclusive sense. Additionally, as used herein, the term "one or more" may be used to describe any feature, structure, or characteristic in singular, or it may be used to describe any combination of features, structures, or characteristics. However, it should be noted that this is merely an illustrative example, and claimed subject matter is not limited to this example. Furthermore, the term "at least one of," when used to associate a list, such as A, B, or C, may be interpreted to mean any combination of A, B, and / or C, such as A, AB, AA, AAB, AABBCCC, etc.

[0069] While several embodiments have been described, various modifications, alternative configurations, and equivalents may be used without departing from the spirit of the present disclosure. For example, the above elements may simply be components of a larger system, where other rules may take precedence over or otherwise modify the application of the various embodiments. Also, some steps may be undertaken before, during, or after the above elements are considered. Therefore, the above description does not limit the scope of the present disclosure.

[0070] In view of this specification, embodiments may include different combinations of features. Example implementations are described in the following numbered clauses. Clause 1. A method of real-time kinematic (RTK) positioning of a mobile device, the method comprising: acquiring a first Global Navigation Satellite System (GNSS) measurement at a first time, the first GNSS measurement including an ionospheric-free carrier phase coupling at a first location of the mobile device; determining a correction term based at least in part on the first GNSS measurement and the first location; acquiring a second GNSS measurement at a second time, the second GNSS measurement including an ionospheric-free carrier phase coupling at a second location of the mobile device; and determining a second location of the mobile device at the second time based at least in part on the second GNSS measurement and the correction term. Clause 2. The method of clause 1, wherein the ionospheric free carrier phase coupling for the first GNSS measurement and the ionospheric free carrier phase coupling for the second GNSS measurement have the same uncertainty term. Clause 3. The method of any of clauses 1-2, wherein the step of determining a second location of the mobile device at a second time is performed without receiving RTK measurement information at a time subsequent to the first time. Clause 4. The method of any of clauses 1-3, further comprising performing inter-satellite single differencing to obtain one or more corrections for one or more errors related to the receiver clock, GNSS inter- / intra-frequency bias and constellation bias, or receiver phase center variation effects, or any combination thereof, and wherein generating the correction terms is further based at least in part on the one or more corrections. Clause 5. The method of any of clauses 1-4, further comprising obtaining correction data from a source that is not an RTK service, the correction data including data enabling orbit correction, clock correction, or both, and wherein generating correction terms is further based at least in part on the correction data. Clause 6. The method of clause 5, where the source is not an RTK service, including another mobile device. Clause 7. The method of any of clauses 1-6, further comprising: determining whether a horizontal position estimation error (HEPE) value exceeds a threshold at a third time; and, in response to determining that the HEPE value exceeds the threshold, requesting RTK measurement information from a base station; and determining a location of the mobile device using the RTK measurement information. Clause 8. The method of any of clauses 1-7, further comprising: determining whether a threshold amount of time has elapsed since the first time; and, in response to determining that the threshold amount of time has elapsed since the first time, requesting RTK measurement information from a base station; and determining a location of the mobile device using the RTK measurement information. Clause 9. The method of any of clauses 1-8, further comprising the steps of: determining whether the mobile device has moved a threshold distance since a first time; and, in response to determining that the mobile device has moved the threshold distance since the first time, requesting RTK measurement information from a base station; and determining a location of the mobile device using the RTK measurement information. Clause 10. The method of any of clauses 1-9, further comprising determining the first location based at least in part on RTK measurement information received from the base station. Clause 11. The method of any of clauses 1-10, further comprising: for each additional time among one or more additional times following the second time, taking a new respective GNSS measurement at each additional time, wherein each new GNSS measurement includes an ionospheric-free carrier phase coupling, and the ionospheric-free carrier phase coupling for the first GNSS measurement and each new GNSS measurement has the same uncertainty term; and determining a location of the mobile device at each additional time based at least in part on the new respective GNSS measurement and the correction term. Clause 12. The method of any of clauses 1 to 11, further comprising the step of determining unavailability of RTK measurement information, wherein the step of determining the correction term is responsive to the step of determining unavailability of RTK measurement information. Clause 13. The method of any of clauses 1-12, further comprising: determining unavailability of RTK measurement information; and, in response to determining unavailability of the RTK measurement information, determining that a determination of a second location of the mobile device is based at least in part on a correction term. Clause 14. A mobile device comprising: a memory; and one or more processing units communicatively coupled to the memory and further communicatively coupled to a Global Navigation Satellite System (GNSS) receiver or configured to implement a GNSS receiver, wherein the one or more processing units are configured to perform the method of any of clauses 1 to 13. Clause 15. A device comprising means for carrying out the method of any of clauses 1 to 13. Clause 16. A non-transitory computer-readable medium having instructions thereon for real-time kinematic (RTK) positioning of a mobile device, the instructions, when executed by one or more processing units, causing the one or more processing units to perform the method of any of clauses 1-13. [Explanation of symbols]

[0071] 110 vehicles 120 Intersection 130 First Location 140 Second Location 150 Travel Route 160 Estimated movement route 170 Estimated movement route 300 RTK System 310 Rover Station 320 base station 330 RF signal 340 Satellite Vehicle (SV), SV 350 Data Communication Network 510 Arrow 520 RTK correction interval 610 North error 620 East error 630 Up error 700 methods 805 Bus 810 Processing Unit 815 output devices 820 Digital Signal Processor (DSP), DSP 830 Wireless Communication Interface 832 Wireless communication antennas, antennas 834 Wireless Signal 840 Sensors 860 memory 870 Input Devices 880 GNSS receiver 882 antenna, individual antenna 884 signal

Claims

1. 1. A method for real-time kinematic (RTK) positioning of a mobile device, comprising: acquiring a first Global Navigation Satellite System (GNSS) measurement at a first time, the first GNSS measurement comprising an ionosphere-free carrier phase coupling at a first location of the mobile device; determining RTK corrections based at least in part on the first GNSS measurement and the first location; acquiring a second GNSS measurement at a second time, the second GNSS measurement including an ionosphere-free carrier phase coupling at a second location of the mobile device; determining the second location of the mobile device at the second time based at least in part on the second GNSS measurement and the RTK correction; determining whether a threshold is exceeded at a third time subsequent to the second time; In response to determining that the threshold is exceeded, requesting first RTK measurement information from a first base station and determining a third location of the mobile device using the first RTK measurement information after the first RTK measurement information is received; and determining that the threshold is exceeded includes: i) determining whether a horizontal position estimation error (HEPE) value exceeds a threshold; or ii) determining whether a threshold amount of time has elapsed since the first time; or iii) determining whether the mobile device has moved a threshold distance since the first time; A method comprising:

2. The method of claim 1 , wherein the ionospheric free carrier phase coupling for the first GNSS measurement and the ionospheric free carrier phase coupling for the second GNSS measurement have the same uncertainty term.

3. 2. The method of claim 1, wherein the step of determining the second location of the mobile device at the second time is performed without receiving second RTK measurement information at a time subsequent to the first time and prior to the second time.

4. 10. The method of claim 1, further comprising performing inter-satellite single differencing to obtain one or more corrections for one or more errors related to a receiver clock, GNSS inter- / intra-frequency bias and constellation bias, or receiver phase center variation effects, or any combination thereof, and wherein determining the RTK correction terms is further based at least in part on the one or more corrections.

5. further comprising obtaining correction data from a source that is not an RTK service; the correction data includes data enabling orbit correction, clock correction, or both; determining the RTK correction term further based at least in part on the correction data; The method of claim 1.

6. A mobile device, Memory and and one or more processing units communicatively coupled to the memory and further communicatively coupled to or configured to execute a Global Navigation Satellite System (GNSS) receiver, the one or more processing units comprising: acquiring, via the GNSS receiver, a first GNSS measurement at a first time, the first GNSS measurement including an ionosphere-free carrier phase coupling at a first location of the mobile device; determining real time kinematic (RTK) correction terms based at least in part on the first GNSS measurement and the first location; acquiring, via the GNSS receiver, a second GNSS measurement at a second time, the second GNSS measurement including an ionosphere-free carrier phase coupling at a second location of the mobile device; determining the second location of the mobile device at the second time based at least in part on the second GNSS measurement and the RTK correction; determining whether a threshold is exceeded at a third time subsequent to the second time; In response to determining that the threshold is exceeded, requesting first RTK measurement information from a first base station, and determining a third location of the mobile device using the first RTK measurement information after the first RTK measurement information is received; configured to: determining that the threshold is exceeded at the third time; i) determining whether a horizontal position estimation error (HEPE) value exceeds a threshold; or ii) determining whether a threshold amount of time has elapsed since the first time; or iii) determining whether the mobile device has moved a threshold distance since the first time; Mobile devices.

7. 7. The mobile device of claim 6, wherein the one or more processing units are further configured to obtain the second GNSS measurement such that the ionosphere-free carrier phase coupling for the first GNSS measurement and the ionosphere-free carrier phase coupling for the second GNSS measurement have the same uncertainty term.

8. 7. The mobile device of claim 6, wherein the one or more processing units are further configured to determine the second location of the mobile device at the second time without receiving second RTK measurement information at a time subsequent to the first time and prior to the second time.

9. The mobile device of claim 6 , further comprising the GNSS receiver.

10. 7. The mobile device of claim 6, wherein the one or more processing units are further configured to perform inter-satellite single differencing to obtain one or more corrections for one or more errors related to a receiver clock, GNSS inter- / intra-frequency bias and constellation bias, or receiver phase center variation effects, or any combination thereof, and wherein the one or more processing units are configured to determine the RTK correction terms based at least in part on the one or more corrections.

11. further comprising a wireless communication interface, wherein the one or more processing units are configured to obtain correction data from a source that is not an RTK service via the wireless communication interface; the correction data includes data enabling orbit correction, clock correction, or both; the one or more processing units are configured to determine the RTK correction terms based at least in part on the correction data. The mobile device of claim 6 .

12. The mobile device of claim 11 , wherein the one or more processing units are configured to obtain the correction data from another mobile device.

13. 7. The mobile device of claim 6, wherein the one or more processing units are further configured to determine the first location based at least in part on second RTK measurement information received from the first base station or a second base station.

14. the one or more processing units, for each additional time period of one or more additional time periods following the second time period, obtaining a new respective GNSS measurement at each additional time, wherein i) the new respective GNSS measurement comprises an ionospheric-free carrier phase coupling, and ii) the ionospheric-free carrier phase coupling for the first GNSS measurement and the new respective GNSS measurement have the same uncertainty term; determining a location of the mobile device at each additional time based at least in part on each new GNSS measurement and the RTK correction; and The mobile device of claim 6 , further configured to:

15. 10. A non-transitory computer-readable storage medium having instructions thereon for real-time kinematic (RTK) positioning of a mobile device, the instructions, when executed by one or more processing units, causing the one or more processing units to perform the method of claim 1.

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