WO2005012937A1

WO2005012937A1 - Method for the satellite-based determination of the position of a user station, user station, device, and computer program

Info

Publication number: WO2005012937A1
Application number: PCT/EP2004/051281
Authority: WO
Inventors: Volker Sommer
Original assignee: Siemens Aktiengesellschaft
Priority date: 2003-08-01
Filing date: 2004-06-29
Publication date: 2005-02-10

Abstract

Disclosed is a method for the satellite-based determination of the position of a user station (UE2). According to said method, the user station (UE2) receives a piece of information (I) from a device (SMLC) of a radio communication system, which indicates from how many satellites the user station (UE2) is to receive signals (S6, S7, S8, S9) for determining the position thereof, and the user station (UE2) receives corresponding signals (S6, S7, S8, S9) only from the indicated number of satellites in order for the position to be determined thereafter.

Description

description

Method for satellite-based position determination of a subscriber station and subscriber station, device and computer program

The invention relates to a method for satellite-based position determination of a subscriber station and a corresponding subscriber station, a corresponding device and a corresponding computer program.

In a conventional satellite-based position determination, for example using GPS (Global Positioning System), a three-dimensional position determination for a subscriber station requires that the distance from the subscriber station to at least four visible satellites is determined. Distance measurements are made indirectly, via transit time measurements of known sequences CDMA (CDMA: Code Division Multiple Access) and known by means of the propagation velocity ^'of electromagnetic waves. In order to be able to determine the signal propagation times from the satellites to the subscriber station exactly, both the time of transmission of the signals and the time of reception in the subscriber station must be known very precisely. While the time of transmission, hereinafter referred to as GPS time, can be decoded from the signals of the satellites by a subscriber station equipped with a complete GPS receiver and can therefore be assumed to be known for determining the position of the subscriber station, the local time base is in the subscriber station, ie the exact time of reception, in

Normally not known and must therefore be obtained by means of an additional measurement. For this reason, a distance measurement to four satellites instead of three satellites is required for a three-dimensional position determination.

Subscriber stations of known radio communication systems, for example according to the GSM (Global System for Mobile Communication) 2003P11536

cations) and the UMTS (Universal Mobile Telecommunications Systems) standard do not have to be equipped with a complete GPS receiver, since they do not decode information from the signals from the satellites. A method called assisted GPS is therefore used to position such subscriber stations. With assisted GPS, the subscriber station only has to carry out runtime measurements by receiving so-called pseudoranges to several satellites. The name pseudoranges comes from the fact that, due to the limited length of the CDMA sequences of the satellite signals, the runtime between the satellites and the subscriber station is known only modulo 1ms. In addition to the signals from the satellites, further information is required to determine the position, for example the navigation data (almanac and ephemeris data) of the satellites. These are determined in the radio communication system, whereby on the one hand the measurement time in the subscriber station can be drastically reduced and on the other hand the required reception field strength of the signals from the satellites is significantly lower than with a normal GPS. In particular, this also enables position determination in buildings.

In radio communication systems with assisted GPS, the GPS time is no longer decoded by the subscriber station of the radio communication system from the signals from the satellites. The

GPS time must therefore either be determined by the radio communication system or the subscriber stations must receive signals from a fifth satellite in order to be able to determine the unknown GPS time using this additional measurement.

The acquisition of at least five satellite signals requires additional measurement effort and measurement time. In certain locations it may even be possible that position determination cannot be carried out if there is no possibility in these locations of receiving signals from at least five satellites. Alternatively, if the GPS time is 2003P11536

communication system determines, this requires that a reference receiver is installed in each radio coverage area of the radio communication system, which determines the GPS time and used for subscriber stations that are located in this radio coverage area.

Thus, in some radio communication systems subscriber stations are used which are designed for a position determination for receiving signals from five satellites, while in other radio communication systems subscriber stations are used which are designed for receiving signals from four satellites.

The object of the invention is a method for satellite-based position determination of a subscriber station and one

To specify a subscriber station, a device and a computer program, which enables the subscriber station to be determined in any radio communication system with as little effort as possible.

This object is achieved with the method, the subscriber station, the device and the computer program according to the independent claims.

Advantageous further developments of the invention are the subject of the dependent claims.

In the method according to the invention for satellite-based position determination of a subscriber station, the subscriber station receives information from a device of a radio communication system, from which number of satellites the subscriber station is to receive signals for its position determination, and the subscriber station receives only the specified number of satellites. appropriate signals for a subsequent position determination. The information enables the subscriber station to use exactly the same amount of energy and measurement time for position determination 2003P11536

consume as required to receive signals from the specified number of satellites. The number specified can depend on which position determination method is implemented in the radio communication system. The subscriber station is enabled by the invention to be operated in any radio communication systems which differ in the number of satellites from which signals for determining the position of the subscriber station must be received. The invention also enables different radio coverage areas (e.g.

Radio cells) of a radio communication system or to specify an individual number of satellites for each position determination.

Another advantage of the invention is that the

Subscriber station does not receive signals from satellites for subsequent positioning if signals from fewer than the specified number of satellites can be received. This avoids unnecessary measurements of signals from an insufficient number of satellites, which do not allow position determination, and possibly signaling information obtained from the signals to a positioning unit of the radio communication system. This situation can occur, for example, if the subscriber station has visual contact with fewer than the specified number of satellites or if signals from satellites cannot be received correctly. The latter means, for example, that a correlation of a reference signal known in the subscriber station with a signal received by a satellite for position determination does not lead to a usable result. The result of this correlation, a so-called pseudorange, is however required to determine the position.

The information received by the device can either specify the number of satellites explicitly or implicitly encode them, for example, using known bit sequences. 2003P11536

In the event that the information is not available at the time of a position determination or was not received or was received only incorrectly, it is advantageous if the subscriber station whenever it does not receive the information prior to a position determination to be carried out, signals for position determination from an im predetermined number of satellites. This ensures that a position can be determined in any case. For example, the predetermined number can be five satellites. On the basis of signals from five satellites and based on the navigation data of the satellites, the coordinates of the subscriber station, ie. H. the geographical longitude, latitude and height as well as the time of transmission and reception of the signals from the satellites are calculated.

In the method according to the invention for satellite-based position determination of a subscriber station, a device of a radio communication system sends information to the subscriber station which can be seen from which number of satellites the subscriber station is to receive signals for its position determination. Depending on the boundary conditions of the radio communication system, a different number of satellites is required for the position determination. According to the invention, the information enables the measurement and computation effort required for determining the position to be reduced to a minimum. The information can be selected so that the minimum number of required satellites is signaled.

In an advantageous embodiment of the invention, the number of satellites to be received depends on at least one item of additional information known for a radio coverage area of the radio communication system, the subscriber station being located in the radio coverage area. Under a radio coverage area, for example, a radio cell of a mobile radio system or generally that area is closed 2003P11536

understand in which a transmitting station of the radio communication system, for example a base station or a further subscriber station, can exchange useful and / or signaling data with the subscriber station via radio waves.

If a time reference of a previous position determination is known as additional information, e.g. B. a reception time of signals from satellites determined in a time base of the radio coverage area, the time difference between the two position determinations can be calculated on the basis of a reception time of signals from satellites of the current position determination measured in the same time base. The time of transmission of the signals from the satellites for the current position determination can be calculated from the time difference and a time of transmission of the signals from the satellites determined during the previous position determination. The current time of transmission therefore no longer has to be determined using signals from satellites, so that the number of satellites required, for example five satellites, can be reduced by one satellite.

Alternatively or additionally, the number of satellites can be reduced by one satellite if only one value of the geographical altitude can occur in the radio coverage area for subscriber stations. The geographic altitude therefore does not have to be determined on the basis of signals from satellites but is taken into account as additional information. The number of satellites can alternatively or additionally be reduced by one satellite if there is a functional connection between the geographical longitude and latitude in the radio coverage area as additional information.

All the additional information mentioned together, ie the time reference, the constant geographic altitude and the functional relationship between longitude and latitude, therefore make it possible to dispense with three satellites. Without the transmitted information, signals from five satellites are required 2003P11536

7 to obtain a solvable system of equations, i.e. H. to be able to determine a position. This results from the fact that in addition to the unknown coordinates, the geographical longitude, latitude and height, the time of transmission and reception of the signals from the satellites must also be calculated. In extreme cases, the information sent only requires two satellites if all of the additional information mentioned above is used.

The subscriber station according to the invention, the device according to the invention and the computer program according to the invention have all the features which are required for carrying out the methods according to the invention.

The invention is explained below with reference to an embodiment shown in Figure 1.

FIG. 1 shows a radio communication system according to the invention, in which the position of a subscriber station is determined according to the invention.

A subscriber station is any station that can receive or send signals. A subscriber station is, for example, a mobile phone or a portable or stationary device for transmitting image and / or sound data, for faxing, sending short messages, SMS and email, and for Internet access. It is therefore a general transmitter and / or receiver unit of a radio communication system.

The invention can advantageously be used in any radio communication system. Radio communication systems are systems in which data is transmitted between stations via a radio interface. The data transmission can be bidirectional as well as unidirectional. Radio communication systems are in particular any mobile radio systems, for example according to the GSM or 2003P11536

the UMTS standard. Future mobile radio systems, for example of the fourth generation, are also to be understood as radio communication systems.

The invention is described below using the example of a mobile radio system according to the UMTS standard, but without being restricted thereto.

FIG. 1 schematically shows a radio communication system according to the invention. In the radio communication system there is a device called a positioning unit SMLC, which controls a position determination of subscriber stations in the radio communication system. In the positioning unit SMLC there is a transmitting and receiving unit SE which can forward data required for a position determination, for example navigation data from satellites to be used for the position determination, to base stations and from there to subscriber stations to be located. If calculations are carried out to determine the position of a subscriber station in the radio communication system, the transmitting and receiving unit SE can receive the data required for this from the subscriber station and carry out the calculations. The necessary data are forwarded to the positioning unit via a base station and, if appropriate, via further stations of the radio communication system.

A first subscriber station UE1 is located in a first radio coverage area FBI of a base station NodeB. The radio communication system uses assisted GPS to determine the position. The time base of synchronized satellites used for position determination, of which five satellites SAT1, SAT2, SAT3, SAT4, SAT5 are shown in FIG. 1, is not known in the radio communication system. The time of transmission of signals from the satellites SAT1, SAT2, SAT3, SAT4, SAT5 required for a satellite-based position determination must therefore be decoded from the signals or made available in some other way. With one for the first part 2003P11536

subscriber station UE1, the first subscriber station UE1 receives a signal S1, S2, S3, S4, S5 simultaneously from each of the five satellites SAT1, SAT2, SAT3, SAT4, SAT5. Using the five signals S1, S2, S3, S4, S5, the position of the first subscriber station UE1 can be determined either in the first subscriber station UE1 or in the positioning unit SMLC. For position determination in the positioning unit SMLC, the information required for position determination is forwarded to the positioning unit SMLC via the base station NodeB.

When the five signals S1, S2, S3, S4, S5 are received, the first subscriber station UE1 also determines a first reception time T1 for the five signals S1, S2, S3, S4, S5 in a time base of the first radio coverage area FBI and divides the first reception time T1 the base station NodeB with. The base station NodeB forwards the first reception time T1 to the positioning unit SMLC for storage.

When determining the first position of the first subscriber station UE1, in addition to its position, a first transmission time, i. H. a first GPS time with the value GPS1, which determines signals S1, S2, S3, S4, S5 and stored, for example, in the positioning unit SMLC. If a second position determination of the first subscriber station UE1 or another subscriber station is carried out in the first radio coverage area FBI, then a second GPS time with the value GPS2 can be used from the first reception time T1 measured during the first position determination and the value GPS1 of the first GPS time Time of the second position determination can be calculated. For this purpose, a value T2 of a second reception time is measured in the time base of the first radio coverage area FBI for signals from satellites that are received during the second position determination. The following then applies: GPS2 = GPS1 + (T2-T1).

By calculating the value GPS2 of the second GPS time, it is no longer necessary to use the second position 2003P11536

10 mung signals from five satellites, but it is sufficient to receive signals from four satellites. However, the time difference between two position determinations may only be so large that a calculation error of the second GPS time, which arises due to an inaccurate, time-drifting, time base of the first radio coverage area FBI, results in a calculation error of the position of the first subscriber station UE1, which is within specified tolerances. The calculation error of the second GPS time is typically tolerable if the time drift in the first radio coverage area FBI does not exceed a few microseconds. If, on the other hand, the time difference between two position determinations is too great, signals from five satellites must be received during the later position determination. The number of satellite signals to be received from subscriber stations is communicated by corresponding information which is sent to the corresponding subscriber station via the positioning unit SMLC and the base station NodeB.

A second subscriber station UE2, whose position is to be determined, is located in a second radio coverage area FB2. For the second radio coverage area FB2, a reception time in a time base of the second radio coverage area FB2 and a GPS time were determined and stored in the positioning unit SMLC during a previous position determination. A GPS time for a position determination currently to be carried out can therefore be calculated on the basis of the data from the previous position determination, as described above. To determine the position of the second subscriber station UE2, it is therefore sufficient to receive signals from only four satellites. For this reason, the positioning unit SMLC sends corresponding information I via the base station NodeB to the second subscriber station UE2. The second subscriber station UE2 can see from the information I that it has to receive signals from only four satellites. 2003P11536

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Without this information I, the second subscriber station would have to receive signals UE2 from a predetermined number of at least five satellites, since then the GPS time would also have to be determined. However, this has a disadvantage if the subscriber station has only four or even fewer satellites available for receiving signals and therefore it does not receive any signals for determining the position and therefore no position determination is carried out. The information therefore has the advantage that a position determination is not limited to a predetermined number of satellites. The number of satellites is determined individually for each position determination, depending on whether and how much additional information the radio communication system has for a current position determination.

In Figure 1, the second subscriber station UE2 receives four signals Sβ, S7, S8, S9 from four satellites SAT2, SAT3, SAT4, SAT5 after evaluating the information I. The calculation of their position is then carried out either by the second subscriber station UE2 itself or by the positioning unit SMLC. For a calculation by the second subscriber station UE2, the previously determined GPS time and the corresponding reception time are possibly communicated to the latter. Conversely, when calculating the position in the positioning unit SMLC, the second subscriber station UE2 transmits all the data obtained from the signals from the satellites for the position determination, for example the time of reception of the signals and pseudoranges determined by correlation measurements, to the positioning unit SMLC.

The information I can of course also be sent to the second subscriber station UE2 if the GPS time is not known, but instead, for example, the second radio coverage area FB2 has a constant geographical height. Subscriber stations in the second radio provider 2003P11536

In this case, the scope of supply is always at the same geographical level. When determining the position of the second subscriber station UE1, only signals from four satellites are likewise received, since an otherwise to be determined size, the geographic height, does not have to be calculated when determining the position.

A constant geographic height in a radio coverage area is either already known from radio network planning or the geographic height within a radio coverage area is determined to be constant if multiple position determinations at different locations in the radio coverage area have always given the same value for the geographic altitude.

Alternatively, the information I can also indicate that only signals from three or even only two satellites are to be received. Signals from three satellites are sufficient for a position determination if the GPS time is known or can be calculated in the radio communication system and the geographic altitude in the radio coverage area is also constant. If there is also a functional connection in the radio coverage area between the geographical longitude and latitude of the position of a subscriber station, only signals from two satellites are required.

Of course, each of the conditions mentioned, alone and in any combination with the other conditions, can determine the number of satellites required for a position determination.

A functional relationship within a radio coverage area can occur if a radio coverage area is a rural area in which, for example, a railroad track or a single main road runs. For a position determination in such a radio coverage area, it can be assumed that a subscriber station is located on the railroad tracks or the main 2003P11536

13 street. The longitude / latitude can now be expressed as latitude / longitude. This functional relationship can be used in particular when a first position determination, for example with five satellites, has established that the subscriber station is actually on the railroad tracks or the main road. If the position is determined further, it can be assumed that the subscriber station continues to follow the train tracks or the main road.

Computer programs can be used to generate and transmit as well as to receive and evaluate the information I, each of which runs in the second subscriber station UE2 or in the positioning unit SMLC, i. H. run on a computer or processor. The computer programs are either loaded into a memory of the second subscriber station UE2 or the positioning unit SMLC from there, or they are located on a data carrier, for example a floppy disk, a CD (compact disc), a DVD (digital versatile disc) or a remote one Server. Access takes place through the second user station UE2 or the positioning unit SMLC via a corresponding reading device or a data line or a radio link.

The second subscriber station UE2 has a receiving unit E and a processor P, the receiving unit E being used to receive the information I and the signals Sβ, S7, S8, S9 of the satellites SAT2, SAT3, SAT4, SAT5 and the information I in the processor P. or the signals S6, S7, S8, S9 are processed. Furthermore, the second subscriber station UE2 naturally has a transmission unit with which it, in the event that the position determination takes place in the positioning unit SMLC, forwards the data required for the position determination to the positioning unit SMLC. 2003P11536

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Of course, the transmitting and receiving unit SE of the positioning unit SMLC can also be arranged in the base station NodeB and accordingly generate the information I or receive signals from subscriber stations and carry out calculations for determining the position in the base station NodeB.

Claims

2003P1153615 claims

1. A method for satellite-based position determination of a subscriber station (UE2), in which - the subscriber station (UE2) receives information (I) from a device (SMLC) of a radio communication system which can be derived from which number of satellites the subscriber station (UE2) signals should receive for their position determination, and - the subscriber station (UE2) only receives corresponding signals (S6, S7, S8, S9) from the specified number of satellites for a subsequent position determination.

2. The method according to claim 1, wherein the subscriber station (UE2) receives signals for determining the position from a predetermined number of satellites whenever it does not receive the information (I) before a position determination to be carried out.

3. Method for satellite-based position determination of a subscriber station, in which a device (SMLC) of a radio communication system sends information (I) to the subscriber station (UE2) which can be seen from which number of satellites the subscriber station (UE2) signals for its Position determination should receive.

4. The method according to claim 3, wherein the number of satellites to be received depends on at least one additional information known for a radio coverage area (FB2) of the radio communication system, the subscriber station (UE2) being located in the radio coverage area (FB2).

5. The method according to claim 4, in which a time reference of a previous position determination is used as additional information. 2003P11536

16

6. The method according to claim 4 or 5, in which information about a constant geographic height for positions of subscriber stations in the radio coverage area (FB2) is used as additional information.

7. The method according to claim 4, 5 or 6, in which a functional relationship between the geographical longitude and latitude is used as additional information.

8. subscriber station (UE2) with a receiving unit (E)

- for receiving information (I) from a device (SMLC) of a radio communication system, which can be seen from which number of satellites the subscriber station (UE2) is to receive signals for determining its position, and

- To receive corresponding signals (S6, S7, S8, S9) for a subsequent position determination only of the specified number of satellites.

9. Device (SMLC) for a radio communication system with a transmitting unit (SE) for sending information (I) to a subscriber station (UE2), which can be seen from which number of satellites the subscriber station (UE2) receive signals for their position determination should.

10. Computer program that when executed in a subscriber station (UE2),

- Information (I) from a device (SMLC) of a radio communication system is used, from which number of satellites the subscriber station (UE2) is to receive signals for its position determination, and

controls the reception of corresponding signals (Sβ, S7, S8, S9) for a subsequent position determination such that the corresponding signals (S6, S7, S8, S9) are only received by the specified number of satellites. 2003P11536

17

11. Computer program which, when executed in a device (SMLC) of a radio communication system, controls a transmission unit (SE) in such a way that the transmission unit (SE) sends information (I) to a subscriber station (UE2), which number can be found from satellites the subscriber station (UE2) should receive signals for their position determination.