DE19537923A1 - Method of generating correction values for user of satellite navigation system - Google Patents

Abstract

The method involves using at least five monitoring stations which are synchronised wrt. time and whose positions are known. Signals from receivable satellites are received in all receiver stations and correction values for the user and satellite positions are derived from the known receiver station positions. The signals are also received by the user. The derived positions are compared with positions indicated by the satellites and an error range determined for the comparisons. For satellites whose indicated positions lie outside the error range an identifier is transmitted to the user.

Description

The invention relates to a method for generating Correction values for a user of a satellite Naviga tion system according to the preamble of claim 1.

The invention is particularly applicable to the Americas niche satellite navigation system GPS ("Global Position ing system "), which is also GPS-NAVSTAR (" Navigation System by Timing And Ranging ") several navigation satellites, currently approximately four and twenty, on predeterminable known earth orbits. Everyone Satellite now transmits periodically at known times score a coded broadcast signal that for every Sa  telliten is a known identifier that characterizes this contains. Every user, e.g. B. on board an aircraft or ship or land vehicle, can now in principle his whereabouts (position), which is divided by three spatial Coordinates is marked, determine that using a satellite navigation receiver in the essentially at the same time, using one-way runtime measurement, the distance to at least three different satellites is measured. This navigation procedure requires

• - That the user (and thus the navigation receiver) in the exact (three-dimensional) position of the Satelli ten knows, at least the positions of those Satelli ten whose transmission signals are evaluated, and
• - That the user (and thus the navigation receiver) so how the satellites always use the same time system, because only then can accurate one-way runtime measurements be made be performed.

These requirements are now particularly important for GPS-NAV STAR takes the following measures:

• - From the operator of the satellites, currently the america Ministry of Defense, is (Satel liten-) headquarters a highly precise so-called system time fixed, for example by means of a so-called atomic atom ren.
• - Each satellite also contains a highly precise one Atomic clock for setting a (satellite) on-board time.
• - The system time and on-board time of a satellite are linked by a (time) indicator that the central for  each satellite is determined individually, and that ever the satellite at predeterminable time intervals, e.g. B. all four hours, transmitted and stored there.
• - From the head office at predeterminable time intervals, e.g. B. also every four hours, for each satellite its so-called ephemeris data, which refer to the Sy stem time related and which the position of Sa include tellites, identified; these are drawn to the transmitted satellite and stored there.
• - The user knows the system time or ideally owns at least one of the system times dependent user time, but ver with the system time is attachable; the latter can be achieved through Emp capture and evaluation of the transmission signals at least one other satellites.

Is now with the user (user recipient) his user time using one of the types mentioned with the system time ge couples, so can at least three satellites Identifiers and associated ephemeris data determined and get saved. Furthermore, from the user for the satellite one-way runtime measurements are made and determined the distances to the satellites will. From the ephemeris data from the satellites and the The measured distance is then the position of the user (User recipient) can be determined.

It can be seen that such a navigation procedure among other things from the agreement and the reliability operator and satellites. Because  system time and / or ephemeris da and / or the (time) characteristics of the satellites visible (systematic) and / or unintentional (random) changed, especially in the case of civil use of the GPS-NAVSTAR incorrect navigation through a Users (user recipients) take place. Such a faulty one Navigation is particularly annoying when only GPS satellite navigation is available and no redundancy, e.g. B. by means of gyro navigation.

Such disturbances can be at least partially corrected are used when using the DGPS ("Differential Global Po sitioning system) navigation system. It is as possible a fixed reference station near the user available. This knows its exact (three-dimensional) bottom sition and also determines the GPS position (position due to the GPS satellite navigation). By a ver the GPS position with the exact position Position correction values determined. These are then the Communicated users, e.g. B. over a radio channel. The user (User recipient) takes this position correction into account then when determining its (user) position based on the GPS satellites carried out by the user navigation. With such a DGPS navigation can before random errors are corrected, z. B. on atmospheric disturbances and / or multipath propagation based on the one-way runtime measurement.

The invention has for its object a genus to specify a procedure that is reliable and systematically in addition to random errors errors can be detected and depending on the  correction errors or at least Mel and the degree of usability Be made available to users.

This problem is solved by the in the characteristic Part of claim 1 specified features. Advantage sticky refinements and / or further training are the further claims removable.

A first advantage of the invention is that all satellites available for a specifiable area monitored and their transmission signals evaluated will.

A second advantage is that a possible mistake can be recognized immediately on a satellite, d. H. even before the operator detects this error and on it indicates.

A third advantage is that navigation ge according to the invention becomes independent in a wide range from the settings of the satellites by the operator.

Further advantages result from the following Be spelling.

The invention is based on the knowledge that the Satelli ten navigation system GPS-NAVSTAR mainly for mili tary applications is designed and therefore currently in Order of the United States Department of Defense is driven. However, they are expressly civilian applications  allowed. In such applications, however, some must high accuracy and high reliability achieved be, for example, with a GPS navigation Airplane approaching landing with poor optical visibility conditions. This high accuracy as well as reliable are present in the GPS system but for civilian users through deliberate manipulation tion of the data so far reduced that civilian users for high accuracy and reliability requirements Must take additional measures, such as the so-called apply the DGPS method. In particular, it must be excluded that accidental and / or systema incorrect settings on at least one satellite incorrect navigation by a civilian user to lead. Such systematic misalignments that are does not affect the operator's military applications from a military point of view, to ir at least temporarily to a military enemy rite. This would inevitably also result in a civilian groove zer irritated. Such systematic errors are in for example, more or less slightly incorrect provided ephemeris data and / or (time) identifiers of the Onboard time of a satellite with respect to the system time that are not accessible to a civilian user.

The invention is illustrated below using an example of explains how to use GPS-NAVSTAR.

In this example it is assumed that a user for his position determination corresponds to a coordinate system based on WGS 72 ("Word Geodetic System 1972").  

For a three-dimensional position determination ei of the user (user receiver) using GPS-NAVSTAR So at least four GPS satellites are needed, namely three Positioning satellites using the disposable device distance measurement and a satellite to determine a loading train at system time. GPS NAVSTAR are currently approximate twenty four working orbiting satellites lanes used so that also by a possible out case of a satellite it is always guaranteed that at least five satellites for positioning can be used. For example, falls during egg ner determination of one of the four satellites, so is always at least in the reception area of a user receiver At least one other satellite is available, with which the Po position determination can be continued.

Below is the letter i, with i = 1, 2, 3. . . to about 24, the unique number of a satellite in the GPS NAVSTAR system. The ephemeris data of the satellite i deliver in connection with the generally known (Kepler formula for the satellite orbit at any time TP the position of the satellite i with respect to the GPS system time, which is also called P-time. Therefore in the following which the letter P uses to refer to the Point out P time.

In Cartesian coordinates (X, Y, Z coordinates) of the WGS 72 is the position (Xi, Yi, Zi) of the satellite i to Time TP can be represented by the formulas:

Xi (TP = (Hi (TP)) sin (βi (TP)) cos (Γi (TP)) (1.1)

Yi (TP = (Hi (TP)) sin (βi (TP)) sin (Γi (TP)) (1.2)

Zi (TP = (Hi (TP)) cos (βi (TP)) (1.3)

Mean (for satellite i in WGS 72 at the moment point TP)

Hi (TP) = distance from the center of the WGS 72 earth ellipsoid,
βi (TP) = northern latitude,
Γi (TP) = east longitude.

It is now assumed that the i existing clock, which delivers a bi-time, regarding the P-time proceeds by the amount DTBi (rate deviation), see above that the time TP can be represented according to the formula

TP = TBi - DTBi (1.4),

where TBi be a predeterminable time in the bi-time points.

To a user N who has the coordinates XN, YN, ZN owns, are from the satellite i its ephemeris the data and its path deviations DTBi communicated so like an average signal speed Cmi in which the state of the earth's atmosphere is taken into account. This Information from satellite i is transmitted to user N. by means of a 50 Hz modulation of the satellite i ordered PRN codes ("Pseudo Random Noise"), which are in the form of the so-called C / A PRN code also for civilian users of the GPS system is accessible. By demodulation in one The user coordinates are the current coordinates Xi (TP), Yi (TP), Zi (TP) of the satellite i at the time TP can be determined, for example also at the time TP = TSPi, where TSPi is a (transmission) time with respect to the  P-time, denotes at which one of the satellites i characteristic place called a timestamp is output in the continuous C / A PRN code stream is sent. The formula applies

TSPi = TSBi - DTBi (1.5),

where TSBi refers to the (send) time of the time stamp which means bi-time (satellite time).

A user receiver contains a user watch, e.g. Legs Quartz watch with at least good short-term stability, which is initially not linked to the system time (P time). It is now assumed that the user clock is moving around the initially unknown amount DTN with respect to the P time. The from satellite i at time TSBi (satellite time) The timestamp of the C / A PRN code is sent out by the groove Receivers received at the time TENi (user time) The runtime DTLi of time sought can be derived from this tag from the satellite i to the user receiver according to the formula

DTLi = (TENi - DTN) - (TSBi - DTBi) (1.6),

only the amount DTN is unknown.

The user receiver (user) stands at four observed Satellites (i = 1 to 4) are four equations with four Unknowns are available, from which the position of the groove can be determined. In Cartesian coordinates of the WGS 72 these are the equations

(XN - Xi) ² + (YN - Yi) ² + (ZN - Zi) ² = (DTMi - DTN) ² · Cmi² (1.7)

With

DTMi = TENi - TSBi + DTBi and i = 1 to 4 (1.8)

But if a satellite doesn't fail completely, it does changes its orbit due to external events an incorrect shift due to an internal partial failure Practice the on-board time (bi-time) compared to the GPS-NAVSTAR-Sy time (P time) then a long time passes span until the error is received from the GPS-NAVSTAR center and via neighboring satellites or via the GPS Information Center (GPSIC) is notified that this Satellite has been blocked for use. During that time span will be the users who are currently receiving the signals from the use faulty satellites to determine position, with non-delimitable errors in your own position determination faced.

In addition, the United States in principle cannot be prevented from using the satellites in military or to instruct civil conflict cases to submit their C / A codes change to make the system unusable. For the civilian users, this case corresponds to a total broken GPS system. There are no corrections to the ge measured position information of the user using the GPS-Sy possible.

Furthermore, the operator can change the C / A-PRN- Code his messages, e.g. For example: ephemeris dates to which Deliberately change users so that a possible counter  ner who ge the GPS system for enemy operations against the operator, at least briefly misguided becomes. The same is done for a civilian user, e.g. B. select rend of a flight approach landing mentioned above stuff. If such misleading is not done in time, he knows, it can be a catastrophic one Damage. Such misleading changes that can also be called systematic errors, are possible on

• - The ephemeris data for the every satellite i as well
• - The time shifts in the clock of each individual Saturday tellites versus the (central) system time, d. H. the Time shifts of the time stamps in the sent Si gnalen.

Such random and / or systematic errors will be recognized in the method according to the invention and corrected that in a particularly interesting Ge offers, e.g. B. in the vicinity of a major airport or even within an entire country, e.g. B. Germany, one of the GPS-NAVSTAR (operator) center completely independent control center is established. This is with at least five control receiving stations, preferably stationary ground stations, coupled. At every control The receiving station is its three-dimensional position knows, e.g. B. from geodetic measurements by laser measurement devices. Each control receiving station is to receive the sent signals from all GPS satellites. The control center and all associated with this Kon troll receiving stations are synchronized in time, i. H. everywhere there is a common control time, which also K-  Time is called, available. This has one at first unknown time lead DTK regarding the P-time. With such an arrangement, time will be consecutive Correction values, which also include the value zero, he averages and communicated to users, e.g. B. via a radio stretch between the control station and the user.

For the mentioned timestamp at the (send) time TSPi (P-time) from the satellite i is located the associated (send) time TSKi in the control time (K time) at

TSKi = TSBi - DTBi + DTK (1.9).

In the Cartesian coordinate system of the WGS 72 has one Control receiving station j a location with the Koordi naten XKj, YKj, ZKj. The control receiving station j emp catches one at time TSPi (P time) from the satellite i sent time stamp at the time TEKÿ (K time) where where the letter E stands for "reception". In the P time is this is the time TEPÿ according to the formula

TEPÿ = TEKÿ - DTK (1.10).

The transit time DTLÿ of a signal, for. B. the time stamp Si gnals, from the satellite i to the control receiving station tion j then results according to the formula

DTLÿ = TEPÿ - TSPi (1.11).

This results in the formula according to formula (1.6)

DTLÿ = (TEKÿ - DTK) - (TSBi - DTBi) (1.12).

In this formula (1.12), the lead DTK is initially unused knows. The size (TEKÿ - TSBi) is measured (one-way run time measurement), and the value DTBi is obtained from the satellite i sent.

Both the communication from Satelli can be incorrect about his ephemeris dates as well as his messages compared to the rate deviation of the satellite clock the GPS system time (P time), d. H. about the temporal ver shift DTBi contained in the transmission signal of satellite i time mark compared to the P time. In the case of an unung Planned (random) error is generally just a single satellite affected by the bug. Will be there gen manipulated, d. H. deliberate (systematic) mistakes generated, several of such manipulations Satellites may be affected, e.g. B. those in one predeterminable period of time in a predeterminable area should lead to faulty navigation.

A user with such a possible manipulation tion calculates, must then take place for its position the correct (error-free) four records of the form

Xi (TSPi), Yi (TSPi), Zi (TSPi) and TSPi

the flawed four records of the form

Xim (TSPim), Yim (TSPim), Zim (TSPim) and TSPim

evaluate, the letter m for "communicated and possible erroneously erroneous and / or manipulated ".

For a faulty gear deviation DTBim in a Sa telliten i applies the formula

DTBi = DTBim - DDTi (2.1)

With

DTBi = actual gear deviation
DDTi = manipulated additional value for the gait deviation.

If the satellite i sends a gear deviation DTBim that by the manipulated additional value DDTi is greater than that actual clock deviation DTBi of own clock from the P-time, then the runtime DTLÿ of the Si is determined gnals (time stamp) from the satellite i to the control Receiving station j using formulas (1.12) and (2.1)

DTLÿ = (TEKÿ - DTK) - (TSBi - DTBim + DDTi) (3.1);

it follows

DTLÿ = TEKÿ - TSBi + DTBim - DTK - DDTi (3.2).

CRi is the actual mean signal speed for one from the satellite i to the control receiving station tion transmitted signal (e.g. the time stamp), then it the distance Rÿ (TSPi) of the satellite i is averaged the control receiving station j according to the formula

Rÿ (TSPi) = DTLÿ · CRi.

By means of the Pythagorean Theorem follows the set of initial equations

(XKj - Xi (TSPi)) ² + (YKj - Yi (TSPi)) ² + (ZKj - Zi (TSPi)) 2 - DTLÿ · CRi) ² = 0 (3.3).

Put one to simplify the spelling

Xi = Xi (TSPi)
Yi = Yi (TSPi)
Zi = Zi (TSPi),

and putting equation (3.2) in equation (3.3), see the formula results

(XKj - Xi) ² + (YKj - Yi) ² + (ZKj - Zi) ² - (TEKÿ - TSBi + DTBim - DTK - DDTi) ² · CRi² = 0 (3.4).

With the abbreviations

DTRÿ = TEKÿ - TSBi + DTBim (3.5)

for the registered time difference and

DTVi = DTK + DDTi (3.6)

for the sum of the shifts you finally get the formula

(XKj - Xi) ² + (YKj - Yi) ² + (ZKj - Zi) ² - (DTRÿ - DTVi) ² · CRi² = 0 (3.7).

In this formula, Xi, Yi, Zi, DTVi and CRi are unknown, so five sizes.  

These are determined by the simultaneous observation of the satellite i from five control receiving stations j, with j = 1 to 5. In the associated control center therefore five equations can be evaluated for each satellite i according to the formulas

(XK1 - Xi) ² + (YK1 - Yi) ² + (ZK1 - Zi) ² - (DTRi1 - DTVi) ² · CRi² = 0

(XK2 - Xi) ² + (YK2 - Yi) ² + (ZK2 - Zi) ² - (DTRi2 - DTVi) ² · CRi² = 0

(XK3 - Xi) ² + (YK3 - Yi) ² + (ZK3 - Zi) ² - (DTRi3 - DTVi) ² · CRi² = 0

(XK4 - Xi) ² + (YK4 - Yi) ² + (ZK4 - Zi) ² - (DTRi4 - DTVi) ² · CRi² = 0

(XK5 - Xi) ² + (YK5 - Yi) ² + (ZK5 - Zi) ² - (DTRi5 - DTVi) ² · CRi² = 0 (3.8)

An evaluation of this system of equations for determination of the five unknown sizes is possible, e.g. B. by means of be known calculations with determinants or data processing MAPLE V (the University of Waterloo, USA). As a result, the sizes Xi, Li, Zi, DTVi and CRi.

CRi is the current average signal speed from i-th satellite to the control stations and can from now on as a better value instead of the vacuum speed of light continue to be used.  

Agree the determined coordinates Xi, Yi and Zi with the Koordi calculated from the ephemeris data provided naten at time TSPi (this is in the K time of time point TSKi) within the error limits, whereby applies

TSKi = TEKÿ + DTVi - DTRÿ,

then the satellite works properly.

If this applies to all observed satellites, then it works the GPS system is faultless.

If the coordinates are determined for a satellite Xi, Yi and Zi with the ephemeris from the communicated calculated coordinates at the time TSPi outside the error limits, then the satellite will not work perfect. This applies to one of the observable satellites liten, this is from the control center for the Use blocked.

Too many satellites are blocked. H. are not anymore enough fault-free satellites can be observed, then, for a sufficient number of satellites, one Be the actual ephemeris data of Sa telliten by Gauß compensation calculation (in conjunction with the general formulas for the satellite orbit) in the Control center determined, if not already on others How the exact ephemeris data were determined.  

For all these satellites is compared by comparison shared ephemeris data with the determined checked whether they only differ in the reference time (system time).

If this is the case, the determined time difference DDTi registered as correction value for the lead DTBim and communicated to users; these can use the satellite continue to use this correction.

If this is not the case, then the communicated Ephemeris data is blocked, and the self-determined ephemeris data (for the P time, the is the K time minus DTVi) for further use by the users communicated.

The control receiving stations also check changes sided whether the DGPS method due to the incorrect data is impaired. If this is the case to a significant extent, then this will be communicated to the users of DGPS.

The invention is not based on the example described limited, but applicable to others, at for example on all satellite systems, for example that Russian satellite system GLONASS, in which a one-way runtime measurement is possible. It is also possible control so-called pseudo-satellites. These are local stations that send satellite signals.

In addition, coordinate systems are different from the one mentioned WGS 72 can be used, for example the coordinate system WGS 84 or the so-called "Potsdam system". Between the  Conversion formulas are known for example the so-called Molodensky formulas.

It is also possible to use an existing GPS reference stations used for the DGPS process, to be used as control receiving stations. Because this GPS reference stations, for example in the area of major airports already have one Arrangement for the reception and evaluation of satellite signals gnalen.

Claims (8)

1. A method for generating correction values for a user of a satellite navigation system, wherein

• a control receiving station with a known position is used,
• at least signals from the satellites that are also used by the user are received in the control receiving station,
• - In the control receiving station from the received Si signals and the known position, a correction value is formed and
• the correction value is transmitted to the user, characterized in that
• that at least five control receiving stations, which are synchronized with respect to time, are used,
• that signals are received from receivable satellites in all control receiving stations and the positions of these satellites are determined from the known positions of the control receiving stations,
• - that the positions determined are compared with those positions which are indicated by the satellite,
• - That an error range is determined for the comparison and
• - That for satellites whose reported position is outside the error range, a label is made, which is transmitted to the user.

2. The method according to claim 1, characterized in that used for navigation satellites of the GPS system will. 3. The method according to claim 1 or claim 2, characterized ge indicates that all control receiving stations ge common time (K time) to the system time (P time) of Sa telliten is coupled. 4. The method according to any one of the preceding claims characterized in that with every receivable Satelli the time offset sent between the on-board time (Bi-time) of the satellite and the system time (P-time) ver It is compared with the corresponding measured time Offset. 5. The method according to any one of the preceding claims characterized in that by means of the control reception possible errors from the signals from the satellites  the data relevant for the navigation of the user and that the errors are communicated to the user the. 6. The method according to any one of the preceding claims, since characterized in that for a satellite that misses sends out learnable data, the corresponding errors to the Users are transmitted and that the satellite under Be consideration of the errors used by the user becomes. 7. The method according to any one of the preceding claims characterized in that with several satellites whose transmitted data are incorrect, by the control emp intercept stations the associated error-free data and that the error-free data and / or on it based correction values are transmitted to the user. 8. The method according to any one of the preceding claims characterized in that at least one satellite, whose sent position data are incorrect, the wrong ler-free position data using a compensation calculation according to Gauss.