WO2011047709A1

WO2011047709A1 - Estimating a position of a stationary radio signal emitter

Info

Publication number: WO2011047709A1
Application number: PCT/EP2009/063667
Authority: WO
Inventors: Olivier Dousse; Niko Kiukkonen; Matti Sakari HÄMÄLÄINEN
Original assignee: Nokia Corporation
Priority date: 2009-10-19
Filing date: 2009-10-19
Publication date: 2011-04-28

Abstract

It is disclosed a method, apparatuses, systems, a program and a readable medium for estimating the position of a stationary emitter. For a point in time a position and a velocity of a moving mobile terminal are determined using a navigation system. For the point in time a value indicative of a Doppler shift of a radio signal observed at the mobile terminal, the radio signal being emitted by the stationary emitter, is also determined. The position of the stationary emitter is estimated based on the determined position of the mobile terminal, the determined velocity of the mobile terminal and on the determined value indicative of the Doppler shift of the radio signal observed at the mobile terminal.

Description

Estimating a Position of a Stationary Radio Signal Emitter

FIELD

This invention relates to estimating a position of a stationary radio signal emitter.

BACKGROUND

Different types of stationary emitters that are capable of emitting radio signals exist. For a variety of applications it is useful to have knowledge on the position of such a stationary emitter available. The position of the stationary emitter is likely to be known by the operator or the proprietor of the emitter. This may however not be the case for other parties. While for a very limited number of stationary emitters it may still be viable to go to the location of the stationary emitter and determine the position thereof by means of a satellite navigation device if the stationary emitters are accessible, such an approach requires significant time and effort if performed for a plurality of stationary emitters.

SUMMARY OF SOME EXEMPLARY EMBODIMENTS OF THE INVENTION

According to a first aspect of the present invention, a method is disclosed. The method comprises determining for a point in time a position and a velocity of a moving mobile terminal using a navigation system; determining for the point in time a value indicative of a Doppler shift of a radio signal observed at the mobile terminal, the radio signal being emitted by a stationary emitter; and estimating the position of the stationary emitter based on the determined position of the mobile terminal, the determined velocity of the mobile terminal and on the determined value indicative of the Doppler shift of the radio signal observed at the mobile terminal. According to a second aspect of the present invention, an apparatus is disclosed. The apparatus comprises means for performing the method according to the first aspect of the present invention. According to a third aspect of the present invention, a further apparatus is disclosed. The apparatus comprises a navigation system navigation module configured to determine for a point in time a position and a velocity of a moving mobile terminal and a frequency analyzer configured to determine for the point in time a value indicative of a Doppler shift of a radio signal observed at the mobile terminal, the radio signal being emitted by a stationary emitter. The navigation system navigation module is configured to provide the determined position of the mobile terminal and the determined velocity of the mobile terminal to a position estimator. The frequency analyzer is configured to provide the determined value indicative of the Doppler shift of the radio signal observed at the mobile terminal to the position estimator. The position estimator is configured to estimate the position of the stationary emitter based on the determined position of the mobile terminal, the determined velocity of the mobile terminal and on the determined value indicative of the Doppler shift of the radio signal observed at the mobile terminal. According to a fourth aspect of the present invention, a further apparatus is disclosed. The apparatus comprises means for determining for a point in time a position and a velocity of a moving mobile terminal; means for determining for the point in time a value indicative of a Doppler shift of a radio signal observed at the mobile terminal, the radio signal being emitted by a stationary emitter; means for providing the determined position and the determined velocity to means for estimating the position of the stationary emitter allocated to the means for determining for a point in time a position and a velocity of a moving mobile terminal; and means for providing the determined value indicative of the Doppler shift of the radio signal observed at the mobile terminal to the means for estimating the position of the stationary emitter allocated to the means for determining for the point in time a value indicative of a Doppler shift of a radio signal observed at the mobile terminal. The means for estimating the position of the stationary emitter comprise means for estimating the position of the stationary emitter based on the determined position of the mobile terminal, the determined velocity of the mobile terminal and on the determined value indicative of the Doppler shift of the radio signal observed at the mobile terminal.

Therein, the means for determining for a point in time a position and a velocity of a moving mobile terminal may for instance be embodied as a navigation system navigation module configured to determine for a point in time a position and a velocity of a moving mobile terminal, but the means are not limited thereto. The navigation system navigation module may, for example, further be configured to provide the determined position of the mobile terminal and the determined velocity of the mobile terminal to the means for estimating the position of the stationary emitter, the navigation system navigation module thus also being an example of the means for providing the determined position and the determined velocity to means for estimating the position of the stationary emitter, but the means are not limited thereto. The means for determining for a point in time a position and a velocity of a moving mobile terminal may also comprise several modules, e.g. a module for position determination and another module for velocity determination. These modules do not have to be arranged within a single device. Furthermore, the means for estimating the position of the stationary emitter may for instance be embodied as a position estimator configured to estimate the position of the stationary emitter, but the means are not limited thereto. Finally, the means for determining for the point in time a value indicative of a Doppler shift of a radio signal observed at the mobile terminal may for instance be embodied as a frequency analyzer configured to determine for the point in time a value indicative of a Doppler shift of a radio signal observed at the mobile terminal, but the means are not limited thereto. The frequency analyzer may, for example, further be configured to provide the determined value indicative of the Doppler shift of the radio signal observed at the mobile terminal to the means for estimating the position of the stationary emitter, the frequency analyzer thus also being an example of the means for providing the determined value indicative of the Doppler shift of the radio signal observed at the mobile terminal to the means for estimating the position of the stationary emitter, but the means are not limited thereto. According to a fifth aspect of the present invention, still another apparatus is disclosed. The apparatus comprises a position estimator configured to estimate the position of a stationary emitter emitting a radio signal based on a position of a moving mobile terminal determined for a point in time, the determined position of the mobile terminal being provided by a navigation system navigation module configured to determine a position of the mobile terminal for the point in time; a velocity of the mobile terminal determined for the point in time, the determined velocity of the mobile terminal being provided by the navigation system navigation module which is further configured to determine the velocity of the mobile terminal for the point in time; and on a value indicative of a Doppler shift of a radio signal observed at the mobile terminal determined for the point in time, the radio signal being emitted by the stationary emitter and the determined value indicative of the Doppler shift of the radio signal observed at the mobile terminal being provided by a frequency analyzer configured to determine for the point in time the value indicative of the Doppler shift of the radio signal observed at the mobile terminal.

According to a sixth aspect of the present invention, a further apparatus is disclosed. The apparatus comprises means for estimating the position of a stationary emitter emitting a radio signal based on a position of a moving mobile terminal determined for a point in time, the determined position of the mobile terminal being provided by means for determining for the point in time a position and a velocity of the moving mobile terminal; a velocity of the moving mobile terminal determined for the point in time, the determined velocity of the mobile terminal being provided by the means for determining for the point in time a position and a velocity of the moving mobile terminal; and on a value indicative of a Doppler shift of a radio signal observed at the mobile terminal determined for the point in time, the radio signal being emitted by the stationary emitter and the determined value indicative of the Doppler shift of the radio signal observed at the mobile terminal being provided by means for determining for the point in time the value indicative of the Doppler shift of the radio signal observed at the mobile terminal.

Furthermore, the means for determining for the point in time a position and a velocity of the moving mobile terminal may for instance be embodied as a navigation system navigation module configured to determine a position of the mobile terminal for the point in time and a velocity of the mobile terminal for the point in time, but the means are not limited thereto. The means for determining for a point in time a position and a velocity of a moving mobile terminal may also comprise several modules, e.g. a module for position determination and another module for velocity determination. These modules do not have to be arranged within a single device . The means for determining for the point in time the value indicative of the Doppler shift of the radio signal observed at the mobile terminal may for instance be embodied as a frequency analyzer configured to determine for the point in time the value indicative of the Doppler shift of the radio signal observed at the mobile terminal, but the means are not limited thereto. Finally, the means for estimating the position of the stationary emitter may for instance be embodied as a position estimator configured to estimate the position of the stationary emitter, but the means are not limited thereto.

According to a seventh aspect of the present invention, a system is disclosed. The system comprises a navigation system navigation module configured to determine for a point in time a position and a velocity of a moving mobile terminal; a frequency analyzer configured to determine for the point in time a value indicative of a Doppler shift of a radio signal observed at the mobile terminal, the radio signal being emitted by a stationary emitter; and a position estimator configured to estimate the position of the stationary emitter based on the determined position of the mobile terminal, the determined velocity of the mobile terminal and on the determined value indicative of the Doppler shift of the radio signal observed at the mobile terminal. According to an eighth aspect of the present invention, a further system is disclosed. The system comprises means for determining for a point in time a position and a velocity of a moving mobile terminal; means for determining for the point in time a value indicative of a Doppler shift of a radio signal observed at the mobile terminal, the radio signal being emitted by a stationary emitter; and means for estimating the position of the stationary emitter based on the determined position of the mobile terminal, the determined velocity of the mobile terminal and on the determined value indicative of the Doppler shift of the radio signal observed at the mobile terminal . Therein, the means for determining for a point in time a position and a velocity of a moving mobile terminal may for instance be embodied as a navigation system navigation module configured to determine for a point in time a position and a velocity of a moving mobile terminal, but the means are not limited thereto. The means for determining for a point in time a position and a velocity of a moving mobile terminal may also comprise several modules, e.g. a module for position determination and another module for velocity determination. These modules do not have to be arranged within a single device .

Furthermore, the means for determining for the point in time a value indicative of a Doppler shift of a radio signal observed at the mobile terminal may for instance be embodied as a frequency analyzer configured to determine for the point in time a value indicative of a Doppler shift of a radio signal observed at the mobile terminal, but the means are not limited thereto .

Finally, the means for estimating the position of the stationary emitter may for instance be embodied as a position estimator configured to estimate the position of the stationary emitter, but the means are not limited thereto.

According to a ninth aspect of the present invention, a program is disclosed. The program comprises program code for performing the method according to the first aspect of the present invention and all exemplary embodiments thereof when the program is executed on a processor. The program may for instance be distributed via a network, such as for instance the Internet.

According to a tenth aspect of the present invention, a readable medium is disclosed. The readable medium has a program according to the ninth aspect of the present invention stored thereon.

The readable storage medium may for instance be a

computer-readable or processor-readable storage medium. It may be embodied as an electric, magnetic, electromagnetic, optic or other storage medium, and may either be a removable storage medium or a storage medium that is fixedly installed in an apparatus or device.

In the following, for the sake of conciseness, the present invention will be explained mainly with respect to the first aspect and the third aspect thereof. These explanations, however, apply accordingly to the other aspects of the invention. It is in particular clear that the explanations given for the elements of the apparatus according to the third aspect of the invention apply accordingly to the

corresponding means of the apparatus according to the fourth aspect of the invention. The same holds with regard to aspects five and six as well as with regard to aspects seven and eight.

According to the above-described aspects of the present invention, the mobile terminal may be a mobile phone, a personal digital assistant (PDA) , a handheld game console, a notebook, a digital music player or a navigation device, to name but a few examples. The stationary emitter is capable of emitting a radio signal. The stationary emitter may, inter alia, be a beacon, an access point or a base transceiver station (BTS) . Non-limiting examples of the stationary emitter are thus a cellular base station, a Wireless Local Area Network (WLAN) access point, a frequency modulation (FM) radio station, or a television (TV) station. The stationary emitter may not only be capable of emitting a radio signal but it may also be capable of receiving radio signals. While the stationary emitter may be an emitter that uses a radio signal for transmitting information to a specific entity or to a plurality of selected entities, e.g. by modulating the radio signal accordingly, information does not necessarily have to be modulated on the radio signal and the stationary emitter does also not have to address the emitted radio signal to specific entities.

The emitter being a stationary emitter may be considered to express that the emitter has a fixed position in a certain frame of reference. For instance, the stationary emitter may be installed in a train in which a user of the mobile terminal is also located. If the train moves, the user of the mobile terminal and the mobile terminal move accordingly. The position of the stationary emitter does thus not change with respect to the user unless the user himself starts moving within the train, e.g. by leaving his seat and walking through the train corridors. Therefore, the emitter is still a stationary emitter.

The radio signal emitted by the stationary emitter naturally has a frequency. Said frequency may for instance be a predetermined frequency. The predetermined frequency does not necessarily have to be a frequency that is constant over time, but it may vary as long as it is known which frequency the radio signal has at a relevant point in time. As an example, the predetermined frequency may be a frequency chosen from a set of predetermined frequencies. Naturally, the frequency of a radio signal may also be expressed in other terms, such as the wavelength of the radio signal.

The radio signal emitted by the stationary emitter may be observed at the mobile terminal. To this end the mobile terminal may comprise means for receiving the radio signal emitted by the stationary emitter. These means may for instance be embodied as a receiver configured to receive the radio signal emitted by the stationary emitter. The mobile terminal does not necessarily have to be a mobile terminal dedicated to receiving the radio signal emitted by the stationary emitter. For example, the mobile terminal may be a mobile phone. The stationary emitter may be a TV station. The radio signal emitted by the TV station may however be observed at the mobile terminal and the observation may serve as a basis for estimating the position of the TV station.

According to all aspects of the present invention, the mobile terminal is a moving mobile terminal. The mobile terminal being a moving mobile terminal may be considered to express that the position of the mobile terminal in a certain frame of reference changes. Within the context of the above example of a user of the mobile terminal being located in a train in which the stationary emitter is installed, the position of the mobile terminal in the frame of reference changes if the user walks, taking the mobile terminal with him, through the corridors of the train. According to the first aspect of the present invention, a position and a velocity of the moving mobile terminal are determined for a point in time. To give but one example, a Global Navigation Satellite System (GNSS) , such as the Global Positioning System (GPS) , the Russian Global Navigation

Satellite System (GLONASS) or the European Galileo system, may be employed to this end.

The apparatus according to the third aspect of the present invention comprises a navigation system navigation module configured to determine for a point in time a position and a velocity of a moving mobile terminal. The navigation system navigation module may also comprise several modules, e.g. a module for position determination and another module for velocity determination. These modules do not have to be arranged within a single device.

The navigation system navigation module may for instance be a GNSS module. As merely one alternative example, the navigation system navigation module may comprise a GNSS module as a first module, the GNSS module being configured to determine for the point in time a position of the moving mobile terminal. A second module may be connectable to a vehicle bus, such as a Controller Area Network (CAN) bus and may obtain via the bus vehicle velocity data from the vehicle's speedometer. Said velocity data may also

characterize the velocity of a mobile terminal located within the vehicle, the second module thus being a module configured to determine for the point in time a velocity of the moving mobile terminal. One may thus still consider the first module together with the second module as a navigation system navigation module configured to determine for a point in time a position and a velocity of a moving mobile terminal.

The determined position and the determined velocity are determined for a point in time, in particular for a same point in time. Due to technical reasons, it may for example not be possible to determine both the position and the velocity of the mobile terminal at exactly the same point in time. The navigation system navigation module may directly determining the velocity of the mobile terminal, e.g. a GNSS such as GPS may provide information on the velocity of a GPS receiver module based on a Doppler shift of the GPS satellite signal. On the other hand, determining the velocity of the mobile terminal may for instance involve determining the position of the mobile terminal at a first point in time and determining the position of the mobile at a second point in time. Based on the temporal difference between the first point in time and the second point in time and based on the spatial distance between the determined position of the mobile terminal at the first point in time and the determined position of the mobile terminal at the second point in time the velocity of the mobile terminal may then be computed. To further increase mobile terminal velocity determination accuracy, averaging of several mobile terminal velocity determination results derived from more than two pairs of temporal and spatial information may be performed.

This approach to determining the velocity of the mobile terminal does not yield the exact position of the mobile terminal at a specific point in time. Yet, the determined velocity may be assigned to a point in time. Said point in time may be the first point in time, the second point in time, the temporal center between the first point in time and the second point in time or any other point in time. The point in time the determined velocity is assigned to is the point in time for which the velocity of the moving mobile terminal is determined.

Accordingly, the position of the moving mobile terminal is determined for the point in time. With the position of the mobile terminal and the velocity of the mobile terminal being determined for the same point in time according to all aspects of the present invention, one may thus also say that the position of the mobile terminal and the velocity of the mobile terminal are assigned to the same point in time.

It is noted that according to all aspects of the present invention, the determined position and the determined velocity of the mobile terminal may be any position and any velocity. The determined position may for instance be a two-dimensional position and the determined velocity may for instance be a two-dimensional velocity. As another example, the determined position may be a three-dimensional position and the determined velocity may be a three-dimensional velocity. The term velocity does however not imply that the determined velocity necessarily has to be a vector, i.e. it does not imply that information on the direction in which the mobile terminal moves has to be obtained. It may suffice to determine merely the magnitude of the velocity of the mobile terminal .

According to the first aspect of the present invention, a value indicative of a Doppler shift of a radio signal observed at the mobile terminal, the radio signal being emitted by the stationary emitter, is determined. To give but one example, a frequency analyzer may be employed to this end. The apparatus according to the third aspect of the present invention comprises a frequency analyzer configured to determine for the point in time a value indicative of a Doppler shift of a radio signal observed at the mobile terminal, the radio signal being emitted by a stationary emitter.

The frequency analyzer may for instance be embodied as a frequency analyzer circuit, comprising for example an accordingly configured field programmable gate array (FPGA) , a digital signal processor (DSP) or an application specific integrated circuit (ASIC) . The frequency analyzer may comprise at least one processor and at least one memory including computer program code, the at least one memory and the computer program code configured to, with the at least one processor, cause the frequency analyzer at least to determine for the point in time a value indicative of a Doppler shift of a radio signal observed at the mobile terminal, the radio signal being emitted by a stationary emitter.

Since the mobile terminal moves when the radio signal emitted by the stationary emitter is observed at the mobile terminal, the frequency of the observed radio signal differs from the frequency of the radio signal upon emission thereof on part of the stationary emitter due to the Doppler effect. The frequency of the radio signal observed at the moving mobile terminal is shifted with respect to the emitted frequency by the Doppler shift, wherein the Doppler shift depends on both the orientation of the velocity vector of the moving mobile terminal and the magnitude thereof.

According to all aspects of the present invention, the value indicative of the Doppler shift of the radio signal observed at the mobile terminal may be any value indicative of the Doppler shift of the radio signal observed at the mobile terminal. Of course, the Doppler shift of the radio signal observed at the mobile terminal itself is a value indicative of the Doppler shift of the radio signal observed at the mobile terminal. As another example, the frequency of the radio signal observed at the mobile terminal is a value indicative of the Doppler shift of the radio signal observed at the mobile terminal, since the Doppler shift may be derived therefrom, e.g. by comparing the frequency of the radio signal observed at the mobile terminal to the frequency of the radio signal emitted by the stationary emitter, which may be a

predetermined or predefined frequency. It may also be possible to encode the frequency of the radio signal upon emission thereof on part of the stationary emitter in the radio signal itself. When observing the radio signal, the mobile terminal may derive the emission frequency therefrom. Just one alternative value indicative of the Doppler shift of the radio signal observed at the mobile terminal is the wavelength of the radio signal observed at the mobile terminal .

The value indicative of the Doppler shift of the radio signal observed at the mobile terminal is determined for the point in time for which the position of the mobile terminal and the velocity of the mobile terminal are also determined. Thus a triple of values, i.e. a set of data, is obtained for the point in time. It comprises the position of the mobile terminal determined for the point in time, the velocity of the mobile terminal determined for the point in time and the value indicative of the Doppler shift of the radio signal observed at the mobile terminal determined for the point in time.

According to the first aspect of the present invention, the position of the stationary emitter is estimated based on the determined position of the mobile terminal, the determined velocity of the mobile terminal and on the determined value indicative of the Doppler shift of the radio signal observed at the mobile terminal. To this end, a position estimator may for instance be employed. The position estimator may for instance comprise a suitably configured FPGA, a DSP or an ASIC. It may comprise at least one processor and at least one memory including computer program code, the at least one memory and the computer program code configured to, with the at least one processor, cause the position estimator to estimate the position of the stationary emitter based on the determined position of the mobile terminal, the determined velocity of the mobile terminal and on the determined value indicative of the Doppler shift of the radio signal observed at the mobile terminal.

In the apparatus according to the third aspect of the invention, the navigation system navigation module is configured to provide the determined position of the mobile terminal and the determined velocity of the mobile terminal to a position estimator. To this end, the navigation system navigation module may for instance comprise means for providing the determined position of the mobile terminal and the determined velocity of the mobile terminal to the position estimator. These means may for example be embodied as a transmitter configured to transmit the determined position of the mobile terminal and the determined velocity of the mobile terminal to the position estimator. As another alternative, the navigation system navigation module may allow the position estimator direct access to the determined position and to the determined velocity, e.g. by storing these values in a memory accessible by the position estimator.

In the apparatus according to the third aspect of the invention the frequency analyzer is configured to provide the determined value indicative of the Doppler shift of the radio signal observed at the mobile terminal to the position estimator. The explanations given on how the navigation system navigation module provides the determined position of the mobile terminal and the determined velocity of the mobile terminal to the position estimator apply accordingly to providing the determined value indicative of the Doppler shift of the radio signal observed at the mobile terminal to the position estimator.

In the position estimation other parameters than the determined position of the mobile terminal, the determined velocity of the mobile terminal and the determined value indicative of the Doppler shift of the radio signal observed at the mobile terminal may be taken into account. In exemplary embodiments according to all aspects of the present invention however, at least the relative direction of the stationary emitter with respect to the determined position of the mobile terminal may be determined exclusively based on the above parameters. An example of how said direction may be obtained is given in the following.

If the mobile terminal moves in a direction that is parallel to the direction of the stationary emitter with respect to the position of the mobile terminal, a maximum Doppler shift will occur. This maximum Doppler shift may be calculated from the magnitude of the velocity of the mobile terminal and the frequency of the radio signal emitted by the stationary emitter, while the actual Doppler shift may be derived from the value indicative of the Doppler shift of the radio signal observed at the mobile terminal. The relationship between the maximum Doppler shift and the actual Doppler shift may be exploited to determine the relative direction of the stationary emitter with respect to the position of the mobile terminal .

Again, it is noted that the determined value triple comprising for a point in time the determined position of the mobile terminal, the determined velocity of the mobile terminal and the determined value indicative of the Doppler shift of the radio signal observed at the mobile terminal may not represent the real values of these parameters exactly, but the values may, for instance, be afflicted with measurement errors. Consequently, the estimated position of the stationary emitter may also not exactly represent the real position of the stationary emitter.

Exemplary embodiments according to all aspects of the present invention may have the advantage of enabling estimation of the position of a stationary emitter emitting a radio signal without having to go to the actual location of the stationary emitter and determine the position thereof, e.g. by means of a navigation device. This is especially beneficial if the positions of a plurality of stationary emitters have to be determined, which would otherwise require significant time and effort. Moreover, the approach according to the present invention may allow for determining the position of non-accessible stationary emitters, for instance stationary emitters that are fenced in. The estimated position of the stationary emitter may be exploited for various purposes. To give but one example, a map of a certain area may be created which comprises location information on stationary radio signal emitters located in that area. No radio signal emitter location information from the operators or the proprietors of the radio signal emitters may be needed for this purpose.

Position estimation or at least some of the steps required for position estimation may be performed transparently to a user of the mobile terminal, e.g. as a background process.

Exemplary embodiments of the method according to the first aspect of the invention comprise at least one of determining the position and the velocity of the mobile terminal for the point in time using navigation system navigation capabilities of the mobile terminal; and determining at the mobile terminal the value indicative of the Doppler shift of the radio signal observed at the mobile terminal. According to exemplary embodiments of the apparatus according to the third aspect of the present invention, at least one of the following conditions is met: the navigation system navigation module forms part of the mobile terminal; and the frequency analyzer forms part of the mobile terminal.

An advantage of these embodiments may be that mobile terminals often have navigation system navigation capabilities, such as GNSS navigation capabilities that may then also be used in the scope of stationary emitter position estimation. For instance, mobile terminals often comprise a navigation system navigation module. Therefore, it may not be required to equip them with additional components to allow for position and velocity determination, thus enabling implementation of the present invention at low costs.

Similarly, mobile terminals often have capabilities for determining at the mobile terminal the value indicative of the Doppler shift of the radio signal observed at the mobile terminal, for instance due to a frequency analyzer forming part of the mobile terminal. According to exemplary embodiments according to all aspects of the present invention the mobile terminal is a mobile communication terminal, the stationary emitter is a stationary communication node and the radio signal is a carrier wave for communication between the stationary communication node and the mobile communication terminal.

Mobile communication terminals are in many cases capable of receiving radio signals emitted by stationary communication nodes. Carrier waves emitted by a stationary communication node for communication between the stationary communication node and the mobile communication terminal often have a predetermined frequency. Mostly standards prescribing a carrier wave frequency exist since this is may be a likely precondition for communication between the stationary emitter and the mobile terminal. Mobile communication terminals are often not only capable of receiving radio signals. Their mode of operation does in many cases comprise determining a value indicative of the Doppler shift of the radio signal observed at the mobile

communication. To name but one example, a channel estimator comprising a frequency analyzer may be provided to allow for proper reception of the carrier wave, for adapting to current radio signal transmission conditions, which may for instance change with the location of the mobile communication terminal, for error correction and for reconstruction of transmitted information, such as speech information or data information .

Nowadays mobile communication terminals are also often provided with mobile navigation capabilities and may therefore in many cases determine their position and their velocity .

It may be especially beneficial to estimate the position of communication node. By doing so, information on the communication node infrastructure in a certain area, including communication nodes operated by different operators, may be gathered. This information may for example be exploited to improve the communication node infrastructure in the respective area. Exemplary embodiments according to all aspects of the present invention comprise determining at least two sets of data for estimating the position of the stationary emitter. According to a first alternative, the first set of data is associated with a first point in time and the second set of data is associated with a second point in time, each set of data comprising for the respective point in time a determined position of the mobile terminal, a determined velocity of the mobile terminal and a determined value indicative of a Doppler shift of the radio signal observed at the mobile terminal.

According to a second alternative, the first set of data is related to a first mobile terminal and the second set of data is related to a second mobile terminal, each set of data comprising for a point in time a determined position of the respective mobile terminal, a determined velocity of the respective mobile terminal and a determined value indicative of a Doppler shift of the radio signal observed at the respective mobile terminal.

Determining two sets of data may be considered as providing a broader data basis for position estimation. Position estimation errors that may be caused, for example, by inaccurate position determination, inaccurate velocity determination or inaccurate determination of the value indicative of the Doppler shift of the radio signal observed at the mobile terminal may thus have less effect on the accuracy of the estimated position.

To give an example, a first position estimate may be obtained by estimating the position of the stationary emitter based on the first set of data in a first step and a second position estimate may be obtained by estimating the position of the stationary emitter based on the second set of data in a second step. Averaging of the first position estimate and the second position estimate may then yield a final unified position estimate. It is also possible to employ more than two sets of data, which may yield even further increased position estimation accuracy. According to the first alternative, the first set of data is associated with a first point in time and the second set of data is associated with a second point in time. Each set of data comprises determined values of the parameters for the respective point in time. This approach allows obtaining two sets of data without requiring two mobile terminals for data acquisition .

In estimating the position of the stationary emitter, weights may then for instance be assigned to the determined values of a parameter, the determined values belonging to different sets of data. Position estimation may then be based on the weighted values.

According to the second alternative, the first set of data is related to a first mobile terminal and the second set of data is related to a second mobile terminal. Each set of data comprises determined values of the parameters for the respective mobile terminal. The values of the two sets of data may be associated with the same point in time or they may be associated with different points in time. This approach may open up the possibility of obtaining significantly more sets of data within a given time frame compared to a scenario in which sets of data are acquired with reference to only one mobile terminal. Considering more sets of data in estimating the position of the stationary emitter may increase the accuracy of the position estimate.

Furthermore, obtaining sets of data for estimating the position of the stationary emitter from different users, the users using different mobile terminals, is enabled.

As another possible advantage of the second alternative, inaccuracies of the determined values caused by

characteristics of the respective mobile terminal may have a reduced effect on the accuracy of the estimated position of the stationary emitter.

An error of a determined value may at least be partly induced by characteristics of the respective mobile terminal. For instance the receivers of mobile terminals, the receivers being configured to receive the radio signal emitted by the stationary emitter, may have different performances. In consequence, the value indicative of the Doppler shift of the radio signal observed at the mobile terminal may be more or less accurately represent the actual Doppler shift of the observed radio signal for different mobile terminals.

Error correlation of a pair of determined mobile terminal positions in two data sets related to different mobile terminals and having been obtained using different entities, e.g. navigation system navigation modules, may be less prominent in comparison to scenarios in which a pair of mobile terminal positions from two data sets is related to the same mobile terminal. Corresponding explanations apply to velocity determination.

According to exemplary embodiments according to all aspects of the present invention which comprises determining two sets of data as explained above, estimating the position of the stationary emitter comprises performing triangulation based on the relative direction of the stationary emitter with respect to the determined position of the mobile terminal derived from the first set of data and based on the relative direction of the stationary emitter with respect to the determined position of the mobile terminal derived from the second set of data. Employing triangulation for estimating the position of the stationary emitter requires only two sets of data, each set of data comprising for a point in time a determined position of a mobile terminal, a determined velocity of said mobile terminal and a determined value indicative of a Doppler shift of the radio signal observed at said mobile terminal. The determined values of the two sets of data may be associated with the same point in time or they may be associated with different points in time. They may or may not relate to the same mobile terminal . However, they may not be associated with the same point in time and be related to the same mobile terminal .

As elucidated above, the relative direction of the stationary emitter with respect to the determined position of the mobile terminal may be determined based exclusively on such a set of data. With two sets of data available, the relative direction of the stationary emitter may also be determined with respect to either another point in time or with respect to a different mobile terminal. In any rate, two positions of a mobile terminal and two associated relative directions of the stationary emitter may be obtained. These four values may the by employed to calculate the position of the stationary emitter by means of triangulation .

According to exemplary embodiments of the method according to the first aspect of the present invention, estimating the position of the stationary emitter comprises determining for the point in time the distance between the mobile terminal and the stationary emitter based on at least one of the propagation delay of the radio signal emitted by the stationary emitter and the path loss of the radio signal emitted by the stationary emitter.

Determining the propagation delay that occurs when the radio signal emitted by the stationary emitter travels from the stationary emitter to the mobile terminal allows calculating the distance between the stationary emitter and the mobile terminal based on the known propagation velocity of the radio signal. To obtain the propagation delay, the radio signal may have a time stamp representative of the time of emission of the radio signal modulated thereon. The time of observing the radio signal at the mobile terminal may also be measured and the propagation delay computed therefrom in a straightforward manner .

Alternatively, the path loss the radio signal emitted by the stationary emitter is subject to on its way to the mobile terminal may be determined. To this end, for instance the power of the radio signal observed at the mobile terminal may be measured, e.g. using a channel estimator forming part of the mobile terminal. Path loss based distance determination may be advantageous in that not necessarily information modulated on the radio signal emitted by the stationary emitter is required to enable distance determination. If distance determination is based on measuring the signal power at the mobile terminal, knowledge of the power of the signal emitted at the stationary emitter, which may be

predetermined, may suffice.

Some exemplary embodiments of the present invention take into account both the propagation delay of the radio signal emitted by the stationary emitter and the path loss of the radio signal emitted by the stationary emitter. This may conduce to obtaining especially accurate distance determination results .

Distance determination may be performed at the mobile terminal or it may not be performed at the mobile terminal.

Since the relative direction of the stationary emitter with respect to the determined position of the mobile terminal may be calculated from the determined position of the mobile terminal, the determined velocity of the mobile terminal and the determined value indicative of the Doppler shift of the radio signal observed at the mobile terminal and since according to the exemplary embodiments of the method according to the first aspect of the present invention currently discussed the distance between the mobile terminal and the stationary emitter is also determined, the position of the stationary emitter may be estimated. No further parameters are necessary to this end. It is in particular not necessary to have two sets of data, each set of data comprising a determined position of a mobile terminal, a determined velocity of said mobile terminal and a determined value indicative of a Doppler shift of the radio signal received at said mobile terminal, available. Consequently, data acquisition for the position estimation may be performed comparatively quickly, Moreover, if the determined values, after having been determined, have to be transmitted to another entity performing position estimation, the

communication load of the channel employed for this purpose may be low.

Estimation of the position of the stationary emitter may also be based on both triangulation and distance determination. The redundancy introduced by this over-determination may be exploited for refinement of the position estimate.

Exemplary embodiments of the apparatus according to the third aspect of the invention comprises a distance estimator configured to determine for the point in time the distance between the mobile terminal and the stationary emitter based on at least one of the propagation delay of the radio signal emitted by the stationary emitter and the path loss of the radio signal emitted by the stationary emitter. According to theses embodiments, the position estimator is configured to also base estimating the position of the stationary emitter on the determined distance.

The distance estimator may for instance be embodied as a distance estimator circuit, comprising for example an accordingly configured FPGA, a DSP or an ASIC. The distance estimator may comprise at least one processor and at least one memory including computer program code, the at least one memory and the computer program code configured to, with the at least one processor, cause the distance estimator at least to determine for the point in time the distance between the mobile terminal and the stationary emitter based on at least one of the propagation delay of the radio signal emitted by the stationary emitter and the path loss of the radio signal emitted by the stationary emitter. Advantages similar to those discussed with respect to the exemplary embodiments of the method according to the first aspect of the present invention that comprise distance determination may arise. According to some exemplary embodiments of the method according to the first aspect of the present invention, estimating the position of the stationary emitter is performed at the mobile terminal. According to some exemplary embodiments of the apparatus according to the third aspect of the present invention, the position estimator forms part of the mobile terminal.

These embodiments may yield the position estimate being available at the mobile terminal directly after estimation has been performed. Transmitting the position estimate from an external entity to the mobile terminal may therefore not be required. The presently discussed embodiments may prove to be of particular advantage if a user of the mobile terminal is interested in being provided with the estimated position of the stationary emitter. If the method according to the first aspect of the present invention also comprises at least one of determining the position and the velocity of the mobile terminal for the point in time using navigation system navigation capabilities of the mobile terminal; and determining at the mobile terminal the value indicative of the Doppler shift of the radio signal observed at the mobile terminal, these values may be processed at the mobile terminal in the course of estimating the position of the stationary emitter. It is then also not required to transmit these values to another entity for further processing. Accordingly, if the method comprises determining for the point in time the distance between the mobile terminal and the stationary emitter, and if this determination is also performed at the mobile terminal, the same advantage may be present.

Similar explanations apply with respect to exemplary embodiments of the apparatus according to the third aspect of the invention that require at least one the following conditions to be met: the navigation system navigation module forms part of the mobile terminal; and the frequency analyzer forms part of the mobile terminal. The same holds for exemplary embodiments of the apparatus, wherein the apparatus comprises a distance estimator configured to determine for the point in time the distance between the mobile terminal and the stationary emitter.

Exemplary embodiments of the method according to the first aspect of the present invention comprise determining reliability information regarding the estimated position of the stationary emitter. According to exemplary embodiments of the apparatus according to the third aspect of the present invention, the position estimator is configured to determine reliability information regarding the estimated position of the stationary emitter.

Reliability information may be any information indicative of the accuracy of the estimated position of the stationary emitter . For example, reliability information may be derived under consideration of the values on which estimating the position of the stationary emitter is based. To give an example, if the determined velocity of the mobile terminal is low, the Doppler effect does not yield a large Doppler shift. This may adversely affect the accuracy of the estimated position of the stationary emitter. Consequently, a value indicating that the determined velocity of the mobile terminal is low, e.g. that it is below a predetermined threshold, may be considered as reliability information regarding the estimated position of the stationary emitter. The determined velocity itself may also be considered as such reliability information.

Moreover, reliability information may for instance be obtained from a plurality of distinct stationary emitter position estimates. Reliability information may be an error metric of the estimated positions of the stationary emitter such as the variance or the standard deviation thereof. The reliability information may also be information on an error correlation of at least two components of the estimated positions of the stationary emitter, such as an x-coordinate (longitude) and a y-coordinate (latitude) . As another example, a probability distribution describing the estimated position of the stationary emitter may be considered as reliability information regarding the estimated position of the stationary emitter. Having estimated the position of the stationary emitter, such reliability information may for instance be obtained by modeling the probability distribution as a probability distribution of a certain, predetermined type, e.g. a Gaussian distribution. It may then be assumed that the estimated position of the stationary emitter constitutes the mean value of the Gaussian distribution. The standard deviation of the distribution may be set based on a priori knowledge. It may for example also be derived from a priori knowledge provided on the errors made in determining the position of the mobile terminal, in determining the velocity of the mobile terminal and in determining the value indicative of the Doppler shift of the radio signal observed at the mobile terminal. This knowledge may for instance in turn be obtained experimentally in view of a ground truth provided on these parameters or by means of computer simulation.

Reliability information regarding an estimated position of the stationary emitter may be provided to a user to inform said user of the reliability of the respective stationary emitter position estimate.

On the other hand, the determined reliability information regarding the estimated position of the stationary emitter may serve for attaining enhanced stationary emitter position estimation accuracy, e.g. by taking the determined reliability information into account when a unified stationary emitter position estimated is to be calculated from several stationary emitter position estimates and the associated reliability information. Therein, the position estimates may for instance relate to different mobile terminals or they may be associated with different points in time.

In some exemplary embodiments of the method according to the first aspect of the present invention at least one of the following three features is realized.

According to the first feature, the method comprises transmitting the estimated position of the stationary emitter to a server.

According to the second feature, the method comprises transmitting the determined position of the mobile terminal, the determined velocity of the mobile terminal, the determined value indicative of the Doppler shift of the radio signal observed at the mobile terminal to a server.

Furthermore, at least one of the determined propagation delay of the radio signal emitted by the stationary emitter, the determined path loss of the radio signal emitted by the stationary emitter, and the determined distance between the determined position of the mobile terminal and the stationary emitter is transmitted to the server. The position of the stationary emitter is estimated at the server based on the transmitted parameters.

According to the third feature, the method comprises determining at least two sets of data. The method further comprises transmitting the at least two sets of data to a server and estimating at the server the position of the stationary emitter based on the transmitted sets of data. Therein one of the following two conditions is met by the two sets of data. The first condition requires that the first set of data is associated with a first point in time and the second set of data is associated with a second point in time, each set of data comprising for the respective point in time a determined position of the mobile terminal, a determined velocity of the mobile terminal and a determined value indicative of a Doppler shift of the radio signal observed at the mobile terminal.

The second condition requires that the first set of data is related to a first mobile terminal and the second set of data is related to a second mobile terminal, each set of data comprising for a point in time a determined position of the respective mobile terminal, a determined velocity of the respective mobile terminal and a determined value indicative of a Doppler shift of the radio signal observed at the respective mobile terminal.

With respect to some of these exemplary embodiments one may thus say that either the estimated position of the stationary emitter is transmitted to a server or that values required for estimating the position of the stationary emitter at the server are transmitted to the server and that position estimation is then performed at the server.

As a result, the determined position of the stationary emitter may then be available at the server allowing, for instance, requesting previously estimated stationary emitter positions at the server. Further advantages may be attained if estimating the position of the stationary emitter is based on at least two sets of data, each set of data comprising a determined position of a mobile terminal, a determined velocity of said mobile terminal and a determined value indicative of a Doppler shift of the radio signal observed at said mobile terminal. Basing estimation of the position of the stationary emitter on a plurality of sets of data may demand more processing power for performing the position estimation than, for example, using just one data set comprising the above values and a determined distance between the determined position of the mobile terminal and the stationary emitter. Providing the required processing power on part of the server may be less challenging than, for instance, providing the required processing power on part of the mobile terminal. The processing power of the server may be employed for other purposes than for estimating the position of the stationary emitter, e.g. if estimating the position of the stationary emitter does not have to be performed at a certain point in time. This may be economically advantageous.

In case of the at least two sets of data estimating the position of the stationary emitter is based on being related to different mobile terminals, the server may serve as a central entity for estimating the position of the stationary emitter. Providing position estimation capabilities on part of the mobile terminals may then not be required. The more mobile terminals the sets of data are related to the more advantageous centralized position estimation may be. In the context of an exemplary embodiment of the method according to the first aspect of the invention comprising transmitting more than one estimated position of the stationary emitter to a server, the server may also compute a unified stationary emitter position estimate, e.g. by selecting one of the transmitted position estimates or by averaging positions estimates.

It is noted that at least some of the values transmitted to the server do not have to be obtained at the mobile terminal, but that no restrictions regarding the entity from which the values are transmitted to the server are made.

If the method according to the first aspect of the present invention comprises transmitting the estimated position of the stationary emitter to a server, previously determined reliability information regarding the estimated position of the stationary emitter may also be transmitted to the server. Similar explanations apply to exemplary embodiments of the apparatus according to the third aspect of the invention, wherein at least one of the following three features is realized. According to the first feature, the apparatus comprises a transmitter configured to transmit the estimated position of the stationary emitter to a server.

According to the second feature, the apparatus comprises a transmitter configured to transmit the determined position of the mobile terminal, the determined velocity of the mobile terminal, the determined value indicative of the Doppler shift of the radio signal observed at the mobile terminal to a sever. In addition, at least one of the determined propagation delay of the radio signal emitted by the stationary emitter, the determined path loss of the radio signal emitted by the stationary emitter and the determined distance between the determined position of the mobile terminal and the stationary emitter is transmitted to the serve. The server comprises a position estimator configured to estimate the position of the stationary emitter based on the transmitted values.

According to the third feature, at least two sets of data are determined. The apparatus further comprises a transmitter configured to transmit the at least two sets of data to a server, the server comprising a position estimator configured to estimate the position of the stationary emitter based on the transmitted sets of data. Therein one of the following two conditions is met by the two sets of data. The first condition requires that the first set of data is associated with a first point in time and the second set of data is associated with a second point in time, each set of data comprising for the respective point in time a determined position of the mobile terminal, a determined velocity of the mobile terminal and a determined value indicative of a Doppler shift of the radio signal observed at the mobile terminal.

The second condition requires that the first set of data is related to a first mobile terminal and the second set of data is related to a second mobile terminal, each set of data comprising for a point in time a determined position of the respective mobile terminal, a determined velocity of the respective mobile terminal and a determined value indicative of a Doppler shift of the radio signal observed at the respective mobile terminal. According to all aspects of the invention, no limitations apply to the technology used for transmitting the data to the server. To give but one example, in the context of exemplary embodiments according to the third aspect of the present invention the transmitter may be a transmitter for wireless communication or it may be a transmitter for wired communication. Any pertinent protocol may be employed for the transmission, e.g. the Internet Protocol (IP).

Some exemplary embodiments of the method according to the first aspect of the present invention comprise transmitting an identifier identifying the stationary emitter from the stationary emitter to the mobile terminal and transmitting the identifier from the mobile terminal to the server. According to exemplary embodiments of the apparatus according to the third aspect of the present invention, the stationary emitter is configured to transmit an identifier identifying the stationary emitter from the stationary emitter to the mobile terminal and the mobile terminal comprises a transmitter configured to transmit the identifier from the mobile terminal to the server.

The transmitter configured to transmit the identifier from the mobile terminal to the server may or may not be the transmitter employed for transmitting the estimated position of the stationary emitter to the sever or employed for transmitting data position estimation may be based on to the sever. Again, no limitations apply to the technology used for transmitting the data to the server.

Transmitting an identifier identifying the stationary emitter from the stationary emitter to the mobile terminal and from the mobile terminal to the sever may enable either associating the estimated position of the stationary emitter transmitted to the server or associating data transmitted to the server for position estimation at the sever with the identifier identifying the stationary emitter. This may contribute to simplifying calculations that are to be performed at the server based on the data transmitted to the server from different entities or at different points in time but related to estimating the position of the same stationary emitter since confusion regarding to which stationary emitter the transmitted data relate may be avoided even if more than one stationary emitter comes into consideration.

In an illustrative scenario, the mobile terminal may be a mobile communication terminal, the stationary emitter may be a stationary communication node associated with a cell of a cellular communication network and the identifier

identifying the stationary emitter may be a cell identifier of the cell associated with the stationary emitter. In this context, the stationary emitter may be a BTS but it does not have to be a BTS. Some of the exemplary embodiments currently discussed may then allow for position estimation of stationary emitters associated with different cells at the server and for distinguishing estimated positions of stationary emitters associated with different cells at the server . It is noted that the mobile terminal does not necessarily have to be associated with the same cell of the cellular network with which the stationary emitter identified by the transmitted cell identifier is associated when transmitting the cell identifier to server. The stationary emitter identified by the cell identifier may for instance be any stationary emitter that the mobile terminal which transmits the cell identifier to the server can hear. Exemplary embodiments of the method according to the first aspect of the invention comprise transmitting an identifier identifying a stationary emitter from the mobile terminal to the server; retrieving at the server the estimated position of the stationary emitter based on the transmitted identifier; and transmitting the retrieved estimated position of the stationary emitter to the mobile terminal having transmitted the identifier.

Correspondingly, according to exemplary embodiments of the apparatus according to the third aspect of the present invention, the mobile terminal comprises a transmitter configured to transmit an identifier identifying a stationary emitter from the mobile terminal to the server; the server is configured to retrieve the estimated position of the stationary emitter based on the transmitted identifier; and the server is configured to transmit the retrieved estimated position of the stationary emitter to the mobile terminal having transmitted the identifier. At the server, estimated positions of stationary emitters may be stored in a database together with identifiers

indentifying the respective stationary emitter. The identifiers may thus serve as a database key. Retrieving an estimated position of a stationary emitter may then be based on a transmitted identifier. The embodiments currently discussed may thus enable providing position data of a stationary emitter to a mobile terminal.

It is noted that the mobile terminal transmitting the identifier and being provided with the retrieved estimated position does not have to have transmitted a position estimate or data position estimation may be based on to the server previously. The mobile terminal does neither have to be capable of determining a value indicative of a Doppler shift of a radio signal observed at the mobile terminal nor does it have to be capable of determining its position or velocity using a navigation system.

The identifier transmitted to the server may identify any stationary emitter. It does not have to identify a stationary emitter the mobile terminal can hear when transmitting the identifier to the server. Yet, the stationary emitter may of course identify a stationary emitter the mobile terminal can hear and the stationary emitter may even transmit its identifier to the mobile terminal for subsequent transmission of the identifier from the mobile terminal to the server.

In this case, and according to some of the currently discussed exemplary embodiments of the invention, the mobile terminal may obtain an estimated position of a stationary emitter that it can hear. Given that the stationary emitter is likely to cover only a limited area, at least coarse information on the position of the mobile terminal may thus be obtained. This localization information may enable providing location based services to a user of the mobile terminal, e.g. to inform the user of the positions of restaurants or cash machines in the users vicinity, even if the respective mobile terminal does not have navigation system navigation capabilities such as GNSS capabilities. On the other hand, such localization information may also be useful if the mobile terminal has navigation system navigation capabilities since two sources of localization information may conduce to obtaining more accurate information on the real position of the mobile terminal, e.g. if the mobile terminal is also capable of estimating its distance to the stationary emitter based on the path loss of the radio signal.

In the illustrative scenario already addressed above, wherein the mobile terminal is a mobile communication terminal, the stationary emitter is a stationary communication node associated with a cell of a cellular communication network and the identifier identifying the stationary emitter is a cell identifier of the cell associated with the stationary emitter, an exemplary embodiment of the method according to the first aspect of the invention may comprise transmitting a cell identifier of a cell of a cellular communication network the mobile terminal is associated with from the mobile terminal to the server; retrieving at the server the estimated position of the stationary emitter associated with the cell based on the transmitted cell identifier; and transmitting the retrieved estimated position of the stationary emitter to the mobile terminal having transmitted the cell identifier . Correspondingly, according to an exemplary embodiment of an apparatus according to the third aspect of the invention the mobile terminal in this context comprises a transmitter configured to transmit a cell identifier of a cell of a cellular communication network a mobile terminal is associated with to the server; the server is configured to retrieve the estimated position of the stationary emitter associated with the cell based on the transmitted cell identifier; and the server is configured to transmit the retrieved estimated position of the stationary emitter to the mobile terminal having transmitted the cell identifier.

These embodiments may thus enable providing position data of a stationary emitter associated with the cell the mobile terminal is also associated with to the mobile terminal.

According to some illustrative embodiments of the method according to the first aspect of the present invention, estimating the position of the stationary emitter is only performed if the determined velocity of the mobile terminal reaches at least a predetermined threshold velocity.

According to exemplary embodiments of the apparatus according to the third aspect of the invention, the position estimator is configured to perform estimating the position of the stationary emitter only if the determined velocity of the mobile terminal reaches at least a predetermined threshold velocity . These embodiments may be understood as comprising that position estimation is only performed if the mobile terminal moves at a sufficiently high rate. If the determined velocity of the mobile terminal is low, the Doppler effect does not yield a large Doppler shift. This may adversely affect the accuracy of the estimated position of the stationary emitter. Only performing estimating the position of the stationary emitter if the determined velocity of the mobile terminal reaches at least a predetermined threshold velocity may help avoiding that low accuracy estimates are obtained. As estimation is not performed if the determined velocity of the mobile terminal does not reach the predetermined threshold velocity, estimation resources are not required in this case. Therefore, the load of a position estimator used for estimating the position of the stationary emitter may be reduced. If the position estimator forms part of the mobile terminal, this may be of particular advantage against the background of mobile terminals often being battery powered because the power consumption of the position estimator and thus of the mobile terminal may be reduced.

If the determined velocity of the mobile terminal does not reach the predetermined threshold velocity, other values for the respective point in time, such as a position of the mobile or a value indicative of a Doppler shift of the radio signal observed at the mobile terminal, may not have to be determined .

Position estimation or obtaining the data position estimation may be based on may be performed automatically if the determined velocity reaches at least the predetermined threshold velocity. On the other hand, performing position estimation does not obligatorily have to be performed even if the determined velocity of the mobile terminal at least reaches the predetermined velocity threshold. According to exemplary embodiments according to all aspects of the present invention, the predetermined threshold velocity is chosen from a range between 1 m/s and 2 m/s. The velocity may in particular be chosen from a range between 1.3 m/s and 1.4 m/s. For instance the threshold velocity may be set to a value close to 5 km/h (1.39 m/s) .

A threshold velocity lower than 1 m/s may not guarantee that stationary emitter position estimates of satisfactory accuracy are obtained. By setting the threshold velocity to a value higher than 2 m/s, slowly moving mobile terminals are excluded from being references for stationary emitter position estimation, which may impede building a

comprehensive stationary emitter position database.

According to an exemplary embodiment of the apparatus according to the third aspect of the present invention, the apparatus is a mobile phone. The mobile phone comprises user interface circuitry and user interface software configured to facilitate user control of at least some functions of the mobile phone through use of a display and configured to respond to user inputs and a display and display circuitry configured to display at least a portion of a user interface of the mobile phone, the display and display circuitry configured to facilitate user control of at least some functions of the mobile phone.

The interface circuitry and the user interface software may for instance allow a user of the mobile phone to request position estimation to be performed and allow presenting an estimated stationary emitter position to the user. The features of the present invention and of its exemplary embodiments as presented above shall also be understood to be disclosed in all possible combinations with each other.

It is to be noted that the above description of embodiments of the present invention is to be understood to be merely exemplary and non-limiting.

Further aspects of the invention will be apparent from and elucidated with reference to the detailed description presented hereinafter.

BRIEF DESCRIPTION OF THE FIGURES

In the figures show: a flowchart of an exemplary embodiment of a method according to the first aspect of the present invention ;

Fig. 2: a schematic illustration of an embodiment of an apparatus according to the third and the fourth aspect of the present invention;

Fig. 3: a schematic illustration of an embodiment of an apparatus according to the fifth and the sixth aspect of the present invention; Fig. 4: a schematic illustration of an exemplary embodiment of another apparatus according to the present invention, the apparatus forming part of a mobile phone ;

Fig. 5: a schematic illustration of triangulation based position estimation using the apparatus of Fig. 4 ;

Fig. 6: a schematic illustration of an exemplary scenario of use of mobile phones similar to the mobile phone of Fig. 4;

Fig. 7: an exemplary flow chart schematically illustrating a method according to the first aspect of the invention in a scenario similar to the scenario depicted in Fig. 6;

Fig. 8: an exemplary flow chart schematically illustrating a method comprising providing a mobile phone with a base transceiver station position estimate stored at a server in the course of performing the method illustrated in Fig. 7 ;

Fig. 9: a schematic illustration of an exemplary embodiment of readable medium according to the tenth aspect of the present invention;

Fig. 10: an illustration of a simulation set-up for testing the accuracy of position estimation according to an exemplary embodiment of the method according to the first aspect of the present invention; Fig. 11: a probability distribution describing the estimated position obtained in the simulation according to Fig. 10.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS OF THE INVENTION

In the following detailed description, exemplary embodiments of the present invention will be described.

Fig. 1 shows a flowchart of an exemplary embodiment of a method according to the first aspect of the present invention.

Step 101 comprises determining for a point in time a position and a velocity of a moving mobile terminal using a navigation system.

Therein, the mobile terminal is a mobile terminal in accordance with the definition given above in the summary of some exemplary embodiments of the invention. The same applies regarding the navigation system navigation module.

Step 102 comprises determining for the point in time a value indicative of a Doppler shift of a radio signal observed at the mobile terminal, the radio signal being emitted by a stationary emitter. To give but one example, a frequency analyzer may be employed to this end.

Therein, the stationary emitter is a stationary emitter in accordance with the definition given above in the summary of some exemplary embodiments of the invention. The same applies to the explanations on the value indicative of a Doppler shift of the radio signal observed at the mobile terminal. The radio signal emitted by the stationary emitter may be observed at the mobile terminal. To this end the mobile terminal may comprise means for receiving the radio signal emitted by the stationary emitter. Since the mobile terminal moves when the radio signal emitted by the stationary emitter is observed at the mobile terminal, the frequency of the observed radio signal differs from the frequency of the radio signal upon emission thereof on part of the stationary emitter due to the Doppler effect. The frequency of the radio signal observed at the moving mobile terminal is shifted with respect to the emitted frequency by the Doppler shift, wherein the Doppler shift depends on both the orientation of the velocity vector of the moving mobile terminal and the magnitude thereof .

A triple of values, i.e. a set of data, is thus obtained for the point in time. It comprises the position of the mobile terminal for the point in time, the velocity of the mobile terminal for the point in time and the value indicative of the Doppler shift of the radio signal observed at the mobile terminal for the point in time.

Step 103 comprises estimating the position of the stationary emitter based on the determined position of the mobile terminal, the determined velocity of the mobile terminal and on the determined value indicative of the Doppler shift of the radio signal observed at the mobile terminal. To this end, a position estimator may for instance be employed.

In the position estimation, other parameters than the determined position of the mobile terminal, the determined velocity of the mobile terminal and the determined value indicative of the Doppler shift of the radio signal observed at the mobile terminal may be taken into account. In the currently discussed exemplary embodiment of a method according to the first aspect of the present invention, at least the relative direction of the stationary emitter with respect to the determined position of the mobile terminal may be determined based exclusively on the above parameters. An example of how said direction may be obtained is given in the following.

Let x_; be the position of the mobile terminal at a point in time denoted by the index i , let v. be the velocity of the mobile terminal at the point in time, let b be the position of the stationary emitter emitting the radio signal having a frequency / and a corresponding wavelength λ and let observed ¹° ^e the frequency of the radio signal observed at the mobile terminal at the point in time. The Doppler shift d_i of the radio signal observed at the mobile terminal at the point in time may then be de rmined using the following equations:

⁼ f ^~ f observed ^■ ( 2 )

Therein the quotient

is a unit vector pointing in the direction from the position b of the stationary emitter to the position x_i of the mobile terminal. The product of said quotient and the velocity of the mobile terminal v. corresponds to the magnitude of the projection of v. in the direction of the unit vector.

Since quotient (3) is a unit vector, the following relationship holds:

Therein, a is the angle between v_i and the unit vector. For the unit vector and v. being parallel, cos a is 1. The Doppler shift d_iparallel is then d. ^paral„lel, = fc ^J . (5)

Knowing the velocity v_i and / or λ , d_iparalM may thus be computed .

With both d_i and d_iparalM being known, a may be determined based on the equation

d,

cosa ( 6 )

^ i, parallel

(note that d_iparallel≠0 due to ||v_f ||≠ 0 since the mobile terminal moves) .

Hence, the direction from the position x_l of the mobile terminal to the position b of the stationary emitter may be determined .

Again, it is noted that the determined value triple comprising for a point in time the determined position of the mobile terminal, the determined velocity of the mobile terminal and the determined value indicative of the Doppler shift of the radio signal observed at the mobile terminal may not represent the real values of these parameters at said point in time exactly, but that the values may be afflicted with measurement errors. Measurement errors may, inter alia, stem from the value determined for a point in time not being equal to the value at said point in time. The measurement errors may for instance be modeled as additive noise.

Let X_i be the position of the mobile terminal determined for the point in time denoted by the index i and let Y_l be a representation of the measurement noise. The relationship between X_i and x_l may then be written as

X_t = x_t + Y_r (6)

With V_i being the position of the mobile terminal determined for the point in time denoted by the index i and with W_l being a representation of the measurement noise, the relationship between V_l and v_l may be written as

ν, = ν, + Ψ, . (7)

Accordingly, let the Doppler shift Ζλ be the value indicative of the Doppler shift of the radio signal observed at the mobile terminal at the point in time determined for the point in time (note that D_t = f - F_{i observed} . holds ; therein F_{i observed} is the observed frequency that may be derived from Ζλ ) and let E_l be the a representation of the error made, the relationship between Ζλ and d_i may be written as D_t=d_t+E_t. (8)

Hence, the direction from the determined position X_i of the mobile terminal to the position b of the stationary emitter may be determined and characterized by the angle A between V_i and a vector pointing in the direction from the position of b stationary emitter to the determined position X_i of the mobile terminal. To this end the following equations may be used :

D i, parallel (9) λ

D,

— = cos A (10)

^ i, parallel The thus obtained estimated direction is likely to not exactly represent the actual direction from the position x_l of the mobile terminal to the position b of the stationary emitter.

The method schematically illustrated in Fig. 1 may have the advantage of enabling estimation of the position of a stationary emitter emitting a radio signal without having to go to the actual location of the stationary emitter and determine the position thereof, e.g. by means of a navigation device. This is especially beneficial if the positions of a plurality of stationary emitters have to be determined, which would otherwise require significant time and effort.

Moreover, this approach may allow for determining the position of non-accessible stationary emitters, for instance stationary emitters that are fenced in. The estimated position of the stationary emitter may be exploited for various purposes. To give but one example, a map of a certain area may be created which comprises location information on stationary radio signal emitters located in that area. No radio signal emitter location information from the operators or the proprietors of the radio signal emitters may be needed for this purpose.

It is noted that step 101 does not necessarily have to be performed before step 102, but that step 102 may also be performed before step 101.

Fig. 2 shows a schematic illustration of an embodiment of an apparatus 200 according to the third and the fourth aspect of the present invention.

The apparatus 200 comprises a navigation system navigation module 201 and a frequency analyzer 202. The navigation system navigation module 201 is configured to determine for a point in time a position and a velocity of a moving mobile terminal. Said navigation system navigation module 201 may for instance be a GNSS module. The navigation system navigation module 201 is configured to provide the determined position of the mobile terminal and the determined velocity of the mobile terminal to a position estimator 301. To this end, the navigation system navigation module 201 may for instance comprise means for providing the determined position of the mobile terminal and the determined velocity of the mobile terminal to the position estimator 301. These means may for example be embodied as a transmitter configured to transmit the determined position of the mobile terminal and the determined velocity of the mobile terminal to the position estimator 301. As another alternative, the navigation system navigation module 201 may allow the position estimator 301 direct access to the determined position and to the determined velocity, e.g. by storing these values in a memory accessible by the position estimator 301.

In the depicted embodiment, the position estimator 301 does not form part of the apparatus 200.

The frequency analyzer 202 is configured to determine for the point in time a value indicative of a Doppler shift of a radio signal observed at the mobile terminal, the radio signal being emitted by a stationary emitter.

The frequency analyzer 202 may for instance be embodied as a frequency analyzer circuit, comprising for example an accordingly configured field programmable gate array (FPGA) , a digital signal processor (DSP) or an application specific integrated circuit (ASIC) . The frequency analyzer may comprise at least one processor and at least one memory including computer program code, the at least one memory and the computer program code configured to, with the at least one processor, cause the frequency analyzer at least to determine for the point in time a value indicative of a Doppler shift of a radio signal observed at the mobile terminal, the radio signal being emitted by a stationary emitter.

The frequency analyzer 202 is further configured to provide the determined value indicative of the Doppler shift of the radio signal observed at the mobile terminal to the position estimator 301. The explanations given on how the navigation system navigation module 201 provides the determined position of the mobile terminal and the determined velocity of the mobile terminal to the position estimator 301 apply accordingly to providing the determined value indicative of the Doppler shift of the radio signal observed at the mobile terminal to the position estimator 301.

The position estimator 301 is configured to estimate the position of the stationary emitter based on the determined position of the mobile terminal, the determined velocity of the mobile terminal and on the determined value indicative of the Doppler shift of the radio signal observed at the mobile terminal . The position estimator 301 may for instance comprise a suitably configured FPGA, a DSP or an ASIC. It may comprise at least one processor and at least one memory including computer program code, the at least one memory and the computer program code configured to, with the at least one processor, cause the position estimator to estimate the position of the stationary emitter based on the determined position of the mobile terminal, the determined velocity of the mobile terminal and on the determined value indicative of the Doppler shift of the radio signal observed at the mobile terminal.

The position estimator 301 may also be seen as an example of means for estimating the position of the stationary emitter. The navigation system navigation module 201 may also be seen as an example of means for determining for a point in time a position and a velocity of a moving mobile terminal. It may also be seen as an example of means for providing the determined position and the determined velocity to means for estimating the position of the stationary emitter. The frequency analyzer 202 may also be seen as an example of means for determining for the point in time a value indicative of a Doppler shift of a radio signal observed at the mobile terminal. It may also be seen as an example of means for providing the determined value indicative of the Doppler shift of the radio signal observed at the mobile terminal to the means for estimating the position of the stationary emitter .

Fig. 3 shows a schematic illustration of an embodiment of an apparatus 300 according to the fifth and the sixth aspect of the present invention.

The apparatus 300 comprises a position estimator 301, corresponding to the position estimator 301 depicted in Fig. 2 and explained with respect thereto. The position estimator 301 is configured to estimate the position of a stationary emitter based on three values.

The first value is a position of a moving mobile terminal determined for a point in time, the determined position of the mobile terminal being provided by the navigation system navigation module 201, which corresponds to the navigation system navigation module shown in Fig. 2 and explained with respect thereto.

The second value is a velocity of the mobile terminal determined for the point in time, the determined velocity of the mobile terminal being provided by the navigation system navigation module 201.

The third value is a value indicative of a Doppler shift of a radio signal observed at the mobile terminal determined for the point in time, the radio signal being emitted by the stationary emitter and the determined value indicative of the Doppler shift of the radio signal observed at the mobile terminal being provided by the frequency analyzer 202, which corresponds to the frequency analyzer shown in Fig. 2 and explained with respect thereto.

In the depicted embodiment, the navigation system navigation module 201 and the frequency analyzer 202 do not form part of the apparatus 300.

The apparatus 300 may also be seen as an embodiment of an apparatus according to the sixth aspect of the present invention .

The apparatus 300 together with the navigation system navigation module 201 and the frequency analyzer 202 may also be seen as an embodiment of a system according to the seventh aspect of the present invention and according to the eighth aspect of the present invention. Moreover, the apparatus 300 together with the navigation system navigation module 201 and the frequency analyzer 202 may also be thought of as an embodiment of an apparatus according to the second aspect of the present invention, the apparatus comprising means for performing the method according to the first aspect of the invention . Fig. 4 shows a schematic illustration of an exemplary embodiment of another apparatus according to the present invention, the apparatus forming part of a mobile phone 400, i.e. a mobile communication terminal.

The apparatus comprises a GPS module 401 connected to an antenna 402 and a transceiver 403 connected to an antenna 406. Furthermore, the apparatus is equipped with a processor 407, a memory 408, a flash memory 409 and a user interface 411. The GPS module 401, the transceiver 403 and the user interface 411 are connected to the processor 407 and the memory 408 via data bus 416.

The user interface 411 of the mobile phone 400 comprises user interface circuitry 412 and user interface software 413 configured to facilitate user control of at least some functions of the mobile phone 400 through use of a display 414 and configured to respond to user inputs and a display 414 and display circuitry 415 configured to display at least a portion of a user interface of the mobile phone 400, the display 414 and the display circuitry 415 configured to facilitate user control of at least some functions of the mobile phone 400. The interface circuitry 412 and the user interface software 413 may for instance allow a user of the mobile phone 400 to request position estimation to be performed and allow presenting an estimated stationary emitter position to the user .

The GPS module 401 is configured to receive GPS satellite signals via antenna 402 and to determine for a point in time a position a velocity of the mobile phone 400 when the mobile phone 400 moves. Via the data bus 416, the GPS module 401 may provide the determined position and the determined velocity of the mobile phone 400 to the memory 408.

On flash memory 409 program code for controlling the GPS module 401 is stored. The Processor 407 is configured to access the flash memory. When the program code stored on flash memory 409 is executed on the processor 407, processor 407 controls the operation of the GPS module 401.

The transceiver 403 comprises a channel estimator 404 and the channel estimator 404 in turn comprises a frequency analyzer circuit 405. By means of the transceiver 403 and the antenna 406 connected thereto, the mobile phone 400 may exchange information modulated on a carrier wave for communication between a stationary emitter and the mobile phone 400, the stationary emitter serving as a stationary communication node .

By estimating the position of the stationary communication node, information on the communication node infrastructure in a certain area, including communication nodes operated by different operators, may be gathered. This information may for example be exploited to improve the communication node infrastructure in the respective area.

In the exemplary embodiment presently discussed, the carrier waves emitted by the stationary communication node for communication between the stationary communication node and the mobile phone 400 have a predetermined frequency, which may be chosen from a set of predetermined frequencies, because the carrier wave frequency is prescribed by a standard.

Mobile phones are likely to be equipped with a transceiver such as the transceiver 403 because a transceiver is needed to allow the mobile phone 400 to serves as a mobile communication terminal. It may therefore not be necessary to provide such a transceiver solely for use in the scope of the present invention.

On flash memory 409 also program code for controlling the transceiver 403 is stored. When the program code stored on flash memory 409 is executed on the processor 407, processor 407 controls the operation of the transceiver 403.

The frequency analyzer circuit 405 is configured to determine for the point in time a value indicative of a Doppler shift of a radio signal observed at the mobile phone 400, the radio signal being emitted by the stationary emitter and having a predetermined frequency. In the present example, the value indicative of the Doppler shift is the frequency of the radio signal observed at the mobile phone 400. By computing the difference between said frequency and the predetermined frequency of the radio signal emitted by the stationary emitter, the Doppler shift may be determined. Via the data bus 416, the transceiver 403 may provide the determined value indicative of the frequency of the radio signal observed at the mobile phone 400 to the memory 408. Beside the program code already referred to above, also program code for estimating the position of the stationary emitter based on the determined position of the mobile phone 400, the determined velocity of the mobile phone 400, the determined value indicative of the frequency of the radio signal observed at the mobile phone 400 and based on the predetermined frequency of the radio signal emitted by the stationary emitter is stored on the flash memory 409. The predetermined frequency of the radio signal emitted by the stationary emitter is also stored on flash memory 409.

When the program code stored on flash memory 409 is executed by the processor 407, the processor estimates the position of the stationary emitter based on the determined position of the mobile phone 400, the determined velocity of the mobile phone 400 and on the determined value indicative of the Doppler shift of the radio signal observed at the mobile phone 400. The required values are taken from the memory 408 and the flash memory 409. After the estimation, the estimated position of the stationary emitter is stored on memory 408.

The processor 407, the memory 408 and the flash memory 409 thus constitute a position estimator 410 configured to estimate the position of the stationary emitter based on the determined position of the mobile phone 400, the determined velocity of the mobile phone 400 and on the determined value indicative of the Doppler shift of the radio signal observed at the mobile phone 400.

As the position estimator 410 forms part of the mobile phone 400, the position estimate is available at the mobile terminal directly after estimation has been performed. Transmitting the position estimate from an external entity to the mobile phone 400 before providing a user of the mobile phone 400 interested in the estimated position of the stationary emitter therewith may therefore not be required. Moreover, with the GPS module 401 and the frequency analyzer circuit 405 also forming part of the mobile terminal, the determined position of the mobile phone 400, the determined velocity thereof and the determined value indicative of the Doppler shift of the radio signal received at the mobile phone 400 do not have to be transmitted from external entities to the mobile phone 400 and the position estimator 410. They may be provided thereto via the data bus 416.

For estimating the position of the stationary emitter at least two sets of data are determined according to the illustrative embodiment of the invention currently discussed. The first set of data is associated with a first point in time and the second set of data is associated with a second point in time, each set of data comprising for the respective point in time a determined position of the mobile phone 400, a determined velocity of the mobile phone 400 and a determined value indicative of the Doppler shift of the radio signal observed at the mobile phone 400. This approach allows obtaining two sets of data without requiring two mobile terminals for data acquisition .

Determining two sets of data may be considered as providing a broader data basis for position estimation. Position estimation errors that may be caused, for example, by inaccurate position determination, inaccurate velocity determination or inaccurate determination of the value indicative of the Doppler shift of the radio signal observed at the mobile phone 400, may thus have less effect on the accuracy of the estimated position. It is also possible to employ more than two sets of data, which may yield even further increased position estimation accuracy. This aspect is elucidated in the following.

Based on the notation introduce above, {xA" , is a sequence of n positions of the mobile phone 400 at points in time denoted by the index i . { ,-}^ is a sequence of velocities of the mobile phone 400 at the points in time and {d_t}"_=l is a sequence of

Doppler shifts, i.e. a sequence of values indicative of the Doppler shifts of the radio signal received at the mobile phone 400 at the points in time. As explained above, the determined sequences of values ^and ^maV ¹°^e afflicted with a certain error or measurement noise.

X + Y (6) V_t=v_t+W_t. (7) D_i=d_i+E_i. (8) The sequence Y^W^E^" is then a measurement noise sequence. With and being determined by the GPS module 401 and {D_i}"__l being determined based on values delivered by the transceiver 403, it may be assumed that the error E_i is independent of the errors Y_i and W_i . The probability of actually measuring X_i , V_i and D. given the truth may be expressed as

which only depends on the distribution of the noises Y_i , W_i and E_i . From Bayesian theory, it is known that

(( 1 »

p({_Xi, v,L, b I ⁽¹²⁾

Assuming that has a uniform distribution yields

It thus follows that

†[

The obtained product form shows that a probability

distribution describing the estimated position of the stationary emitter, and consequently the estimated position of the stationary emitter itself, may be refined successively by basing estimation of the position of the stationary emitter on at least two sets of data.

Furthermore, with two set of data being provided, stationary emitter position estimation by means of triangulation is enabled. To this end, the position estimator 410 is configured to estimate the position of the stationary emitter by performing triangulation based on the relative direction of the stationary emitter with respect to the determined position of the mobile phone 400 derived from the first set of data and based on the relative direction of the stationary emitter with respect to the determined position of the mobile phone 400 derived from the second set of data.

For each obtained pair of data sets, the position estimator 410 estimates a position of the stationary emitter.

Fig. 5 is a schematic illustration of triangulation based position estimation using the mobile phone of Fig. 4.

The mobile phone 400 moves along the trajectory s. For the first point in time the determined position of the mobile phone 400 is point A, while for the second point in time the determined position of the mobile phone 400 is point B. Based exclusively on the two sets of data, the relative direction of the stationary emitter with respect to the determined position A of the mobile phone 400 may be determined and described in terms of the angle a, as explained above. Accordingly, the relative direction of the stationary emitter with respect to the determined position B of the mobile phone 400 may be determined and described in terms of the angle β. Knowing these directions, the estimated position C of the stationary emitter may be obtained.

Returning to the discussion of Fig. 4, the position estimator 410 depicted therein is configured to perform estimating the position of the stationary emitter only if the determined velocity of the mobile phone 400 reaches at least a predetermined threshold velocity. If the determined velocity of the phone 400 is low, the Doppler effect does not yield a large Doppler shift. This may adversely affect the accuracy of the estimated position of the stationary emitter. Only performing estimating the position of the stationary emitter if the determined velocity of the mobile terminal reaches at least a predetermined threshold velocity may help avoiding that low accuracy estimates are obtained. As estimation is not performed if the determined velocity of the mobile phone 400 does not reach the predetermined threshold velocity, the position estimator 410 discards the values determined for the respective point in time. Therefore, the load of the position estimator 410 is reduced. Since the position estimator 410 forms part of the mobile phone 400, which is in this case battery powered, it is beneficial that the power consumption of the position estimator 410 and thus of the mobile phone 400 may thereby be reduced.

The predetermined threshold velocity is chosen from a range between 1 m/s and 2 m/s, namely it is set to the value of 1.39 m/s (5 km/h) . A threshold velocity lower than 1 m/s may not guarantee that stationary emitter position estimates of satisfactory accuracy are obtained. By setting the threshold velocity to a value higher than 2 m/s, the velocity may not reach the predetermined threshold during periods of significant length, e.g. if the user of the mobile phone 400 walks while carrying the mobile phone 400. In theses periods, no position estimates are obtained which may be detrimental to gathering a satisfactory data basis of stationary emitter position estimates. In another embodiment, the channel estimator 404 of the transceiver 403 may also be configured to determine the propagation delay of the radio signal emitted by the stationary emitter or to determine the path loss of the radio signal emitted by the stationary emitter by measuring the signal strength of the radio signal received by transceiver 403 or determining at which point in time the radio signal is received, respectively. Comparison to the signal strength provided by the stationary emitter or, respectively, to the time of the signal emission, then yields the path loss or the propagation delay.

The position estimator 410 may then additionally serve as a distance estimator and determine for the point in time the distance between the mobile terminal and the stationary emitter and also base estimating the position of the stationary emitter on the thus determined distance.

The transceiver 403 is configured to transmit each estimated position of the stationary emitter to a server (not shown in Fig. 4) .

As a result, the determined position of the stationary emitter may then be available at the server allowing, for instance, requesting previously estimated stationary emitter positions at the server. The server may process the transmitted estimated positions of the stationary emitter to obtain a single estimated position of the stationary emitter. For instance, averaging of the position estimates may yield a unified stationary emitter position estimate. The position estimator 410 is configured to determine reliability information regarding the estimated position of the stationary emitter. Reliability information may be any information indicative of the accuracy of the estimated position of the stationary emitter.

In the embodiment depicted in Fig. 4, the position estimator 410 is configured to determine a probability distribution describing the estimated position of the stationary emitter as reliability information regarding the estimated position of the stationary emitter. The probability distribution is modeled as a Gaussian distribution. Therein, the estimated position of the stationary emitter constitutes the mean value of the Gaussian distribution. The standard deviation of the distribution is set based on a priori knowledge. Said a priori knowledge is derived from a priori knowledge provided on the errors made in determining the position of the mobile phone 400, in determining the velocity of the mobile phone 400 and in determining the value indicative of the Doppler shift of the radio signal observed at the mobile phone 400. The standard deviation of the distribution is expressed in terms of the standard deviation of the longitude (longitude error) , the standard deviation of the latitude (latitude error) and the correlation of the longitude error and the latitude error. Reliability information is determined for each estimated position of the stationary emitter.

Reliability information regarding each estimated position of the stationary emitter may be presented to a user of the mobile phone 400 on the display 414 to inform said user of the reliability of the respective stationary emitter position estimate . The transceiver 403 is configured to transmit the reliability information to the server. The determined reliability information regarding the estimated position of the stationary emitter may serve for attaining enhanced stationary emitter position estimation accuracy.

In practice, successive sets of stationary emitter position estimates and reliability information in form of a

probability distribution may be determined by the mobile terminal 400 when moving. A combined probability distribution describing the estimated position of the stationary emitter may, as may be derived from equation (14) , be simply obtained by multiplying the distributions associated with the each of the estimated positions. Iterative refinement of the estimated position of the stationary emitter is thus possible .

Fig. 6 shows a schematic illustration of an exemplary scenario of use of mobile phones 400-1 to 400-5 similar to the mobile phone 400 of Fig. 4.

In the exemplary scenario, two stationary emitters BTS-1 and BTS-2 emitting radio signals, each radio signal having a predetermined frequency chosen from a set of predetermined frequencies, are provided. The stationary emitters BTS-1 and BTS-2 are stationary communication nodes. BTS-1 is a base transceiver station associated with a cell C-l of a cellular communication network and BTS-2 is a base transceiver station associated with a cell C-2 of the cellular communication network. Both BTS-1 and BTS-2 are connected to a server 600. The server 600 comprises a processor 601, a memory 602 and a hard disk 603.

The mobile phones 400-1 to 400-5 resemble the mobile phone 400 depicted in Fig. 4. The mobile phones 400-1, 400-2 and 400-3 are associated with the cell C-1 of the cellular network. This is visualized in Fig. 6 by the ellipse denoted by the reference sign C-1 and encompassing the mobile phones 400-1, 400-2 and 400-3. The mobile phones 400-4 and 400-5 are associated with the cell C-2 of the cellular communication network. Each of the mobile phones 400-1 to 400-5 is able to hear the base transceiver station of its respective cell. Cell C-1 is identified by a cell identifier 1-1, while cell C-2 is identified by a cell identifier 1-2. Due to the base transceiver station BTS-1 being associated with cell C-1, the identifier 1-1 of the cell C-1 also identifies the base transceiver station BTS-1 and the identifier 1-2 of the cell C-2 also identifies the base transceiver station BTS-2. The mobile phones 400-1 to 400-3 estimate, when moving at a sufficiently high rate, the position of base transceiver station BTS-1 and transmit the position estimates and reliability information regarding the position estimates of base transceiver station BTS-1 to the server 600.

BTS-1 is configured to transmit the cell identifier 1-1 to the mobile phones 400-1 to 400-3 associated with cell C-1. The mobile phones 401-1 to 400-3 each comprises a transceiver corresponding to the transceiver 403 of the mobile phone 400 of Fig. 4. The transceiver is configured to receive the transmitted cell identifier 1-1 and to transmit the cell identifier 1-1 to the server 600 via base transceiver station BTS-1. The mobile phones 400-4 and 400-5 behave accordingly with respect to base transceiver station BTS-2 and cell C-2.

With the mobile phones 400-1 to 400-3 transmitting the cell identifier 1-1 together with their estimates of the position of the base transceiver station BTS-1 and with the mobile phones 400-4 and 400-5 transmitting the cell identifier 1-2 together with their estimates of the position of the base transceiver station BTS-2, the sever 600 may distinguish estimated positions of base transceiver station BTS-1 and base transceiver station BTS-2.

As explained above, each of the mobile phones 400-1 to 400-5 transmits position estimates obtained based on data sets associated with different points in time. The position estimates transmitted by mobile phone 400-1 are related to mobile phone 400-1, while the position estimates transmitted by the other mobile phones 400-2 to 400-5 are related to the mobile phones 400-2 to 400-5, respectively. This approach may open up the possibility of obtaining significantly more position estimates within a given time frame compared to a scenario in which position estimates are provided by only one mobile phone. The server 600 serves as a central entity for calculating unified estimated positions of the base transceiver stations BTS-1 and BTS-2. On hard disk 603 program code for calculating a unified estimate of the position of the base transceiver station BTS-1 and a unified estimate the position of the base transceiver station BTS-2 is provided. The Processor 601 is configured to access the hard disk 603. When the program code stored on the hard disk 603 is executed on the processor 601, the processor 601 calculates a unified estimate of the position of the base transceiver station BTS-1 and a unified estimate of the position of the base transceiver station BTS-2. This is achieved by multiplying the probability distributions obtained from the transmitted estimated positions and the reliability information regarding the respective estimated positions. It may be advantageous to determine the unified position estimates on part of the server 600. Providing capabilities for calculating a unified position estimate for each of the base transceiver stations BTS-1 and BTS-2 on part of the mobile phones 400-1 to 400-5 may then not be required. The more mobile phones the sets of data are related to, the more advantageous centralized unified estimated position calculation may be. Providing the required processing power on part of the server 600 may be less challenging than, for instance, providing the required processing power on part of one of the mobile phones associated with the cell of the respective base transceiver station. The processing power of the server 600 may be employed for other purposes than for calculating unified estimated positions of the base transceiver stations BTS-1 and BTS-2, e.g. if estimating the positions of the base transceiver stations BTS-1 and BTS-2 does not have to be performed at a certain point in time. This may be economically advantageous.

Due to a plurality of mobile phones 400-1 to 400-3 being employed for estimating the position of the base transceiver station BTS-1, inaccuracies of the determined values on which position estimation is based on part of the mobile phones 400-1 to 400-3, the inaccuracies caused by characteristics of the respective mobile phones 400-1 to 400-3, may have a reduced effect on the accuracy of the unified estimated position of the base transceiver station BTS-1.

An error of a determined value may at least be partly induced by characteristics of the respective mobile phone. For instance the transceivers of mobile phones (see transceiver 403 in Fig. 4) may have different performances. In consequence, the values indicative of the Doppler shift of the radio signal observed at the mobile phones 400-1 to 400-3 may more or less accurately represent the actual Doppler shift of the observed radio signal for different mobile phones. Since different transceivers are used for determining values indicative of the Doppler shift of the radio signal received at the different mobile phones, the error correlation of these values may be reduced in comparison, for instance, to values indicative of the Doppler shift of the radio signal observed at a single mobile phone but determined for different points in time. Similar advantages may arise with respect to position and velocity determination of the mobile phones 400-1 to 400-3. The above explanations also apply to mobile phones 400-4 and 400-5.

At the server 600, unified estimated positions of the base transceiver stations BTS-1 and BTS-2 are stored in a database 604 on the hard disk 603 together with the cell identifiers 1-1 and 1-2, respectively. The unified estimated position of base transceiver station BTS-1 is stored in form of a coordinate pair (X_lrY₁) and associated reliability

information. Therein, X₁ is the longitude of the unified estimated position and Y i is the latitude of the unified estimated position. The unified estimated position of base transceiver station BTS-2 is stored as the coordinate pair (X2_/Y2) · The cell identifiers 1-1 and 1-2 serve as a database key. Retrieving a unified estimated position of a base transceiver station may then be based on a cell identifier. The transceiver 403 of the mobile phone 400 depicted in Fig. 4 is configured to transmit a cell identifier identifying one of the base transceiver stations BTS-1 and BTS-2 to the server 600. With the mobile phones 400-1 to 400-5 in Fig. 6 being similar to the mobile phone 400 of Fig. 4, the mobile phones 400-1 to 400-5 are also capable of transmitting a cell identifier to the server 600. The server 600 is configured to retrieve the estimated position of the base transceiver station associated with the cell identified by the

transmitted cell identifier based on the transmitted cell identifier. Furthermore, the server 600 is configured to transmit the retrieved estimated position of the respective base transceiver station to the mobile phone having transmitted the identifier via the base transceiver station associated with the cell with which the respective mobile phone is also associated.

Thus position data of a base transceiver station may be provided to a mobile phone. The mobile phone may obtain an estimated position of the base transceiver station associated with the cell with which the respective mobile phone is also associated. Given that the base transceiver station in the exemplary scenario illustrated in Fig. 6 covers only a limited area, at least coarse information on the position of the mobile phone may thus be obtained.

It is noted that in an alternative scenario, at least one of the mobile phones 400-1 to 400-5 does not transmit an estimated base transceiver station position to the server 600, but the determined position of the mobile phone, the determined velocity of the mobile phone, the determined value indicative of the Doppler shift of the radio signal observed at the mobile phone and at least one of the determined propagation delay of the radio signal emitted by the respective base transceiver station, the determined path loss of the radio signal emitted by the respective base transceiver station and the determined distance between the determined position of the mobile phone and the respective base transceiver station. The position of the respective base transceiver station may then be estimated at the server 600 using the processor 601 and the memory 602 and program code stored on the hard disk 603 to this end.

Alternatively, at least two sets of data may be transmitted to the server 600. According to a first approach, the first set of data is associated with a first point in time and the second set of data is associated with a second point in time, each set of data comprising for the respective point in time a determined position of the mobile phone, a determined velocity of the mobile phone and a determined value indicative of a Doppler shift of the radio signal observed at the mobile phone. According to a second approach, the first set of data is related to a first mobile phone and the second set of data is related to a second mobile phone, each set of data comprising for a point in time a determined position of the respective mobile phone, a determined velocity of the respective mobile phone and a determined value indicative of the Doppler shift of the radio signal observed at the respective mobile phone. The server 600 may then estimate the position of the respective base transceiver station based on the transmitted sets of data, e.g. by means of triangulation .

It is also possible to transmit position estimates from some of the mobile phones 400-1 to 400-5 to the server 600, while others transmit only data position estimation may be based on to the server 600. Furthermore, some of the mobile phones 400-1 to 400-5 may even transmit both. It is also not required that the transmitting mobile terminals are all mobile phones. For example, notebooks and personal digital assistants may also transmit position estimates or data for position estimation to the server 600 and the transmitted values may be processed together with those transmitted from the mobile phones 400-1 to 400-5.

Fig. 7 shows an exemplary flow chart schematically

illustrating a method according to the first aspect of the invention in a scenario similar to the scenario depicted in Fig. 6.

Step 701 comprises determining for a point in time a position and a velocity of a moving mobile phone using navigation system navigation capabilities of the mobile phone. In step 702, a radio signal, the radio signal being emitted by a base transceiver station, and a cell identifier identifying the base transceiver station are received at the mobile phone. The radio signal is a carrier wave for communication between the base transceiver station and the mobile phone and the radio signal has a predetermined frequency . Step 703 comprises determining at the mobile phone for the point in time a value indicative of a frequency of a radio signal observed, i.e. received, at the mobile phone.

Therefrom a value indicative of a Doppler shift of the radio signal received at the mobile phone is calculated by subtracting the predetermined frequency of the radio signal emitted by the stationary emitter.

In step 704 it is checked whether or not the determined velocity reaches at least a predetermined threshold velocity, which is in this case set to 1.39 m/s . If the check does not yield a positive result, the determined position, the determined velocity and the determined value indicative of the Doppler shift of the radio signal observed at the mobile phone are discarded.

However, if the determined velocity is at least 1.39 m/s, steps 701-704 are repeated to obtain a second set of data, the second set of data being associated with a second point in time and in turn comprising for the second point in time a determined position of the mobile phone, a determined velocity of the mobile phone and a determined value indicative of the Doppler shift of the radio signal observed at the mobile phone .

In step 705, based on the thus obtained two sets of data, the first set of data being associated with a first point in time and the second set of data being associated with a second point in time, each set of data comprising for the respective point in time a determined position of the mobile phone, a determined velocity of the mobile phone and a determined value indicative of the Doppler shift of the radio signal observed at the mobile phone, the position of the base transceiver station is estimated at the mobile phone. To this end, triangulation is performed based on the relative direction of the base transceiver station with respect to the determined position of the mobile phone derived from the first set of data and based on the relative direction of the base transceiver station with respect to the determined position of the mobile phone derived from the second set of data. Step 706 comprises determining reliability information regarding the estimated position of the base transceiver station .

In step 707, the estimated position of the base transceiver station, the determined reliability information and the cell identifier are transmitted to a server. Steps 701-707 are performed by a plurality of mobile terminals so that a plurality of position estimates for the base transceiver station is transmitted to the server. The server determines a unified position estimate based on the position estimates and under consideration of the transmitted reliability information in step 708. In step 709, the unified base transceiver station position estimate is stored together with the cell identifier in a database.

Further position estimates transmitted to the server by a mobile phone may be used to refine the stored unified position estimate and to overwrite the stored unified position estimate with the refined position estimate.

Fig. 8 show an exemplary flow chart schematically

illustrating a method comprising providing a mobile phone with a base transceiver station position estimate stored at a server in the course of performing the method illustrated in Fig . 7. In step 801 a mobile phone transmits a cell identifier to the server. The server retrieves the estimated position of the base transceiver station based on the transmitted cell identifier in step 802 and transmits the retrieved estimated position of the base transceiver station, which may be a unified estimated position, to the mobile phone having transmitted the cell identifier.

Fig. 9 is a schematic illustration of an exemplary embodiment of readable medium 900 according to the tenth aspect of the present invention.

On the readable medium 900 a computer program 901 is stored. The computer program 901 comprises program code 902 for performing the method according the first aspect of the present invention when the program is executed on a processor. Namely, the program code 902 comprises code for determining for a point in time a position and a velocity of a moving mobile terminal using a navigation system; for determining for the point in time a value indicative of a Doppler shift of a radio signal observed at the mobile terminal, the radio signal being emitted by a stationary emitter; and for estimating the position of the stationary emitter based on the determined position of the mobile terminal, the determined velocity of the mobile terminal and on the determined value indicative of the Doppler shift of the radio signal observed at the mobile terminal . Readable medium 900 is for instance a computer-readable or processor-readable medium. Readable medium 900 may for instance be embodied as an electric, magnetic,

electro-magnetic, optic or other readable medium, and may either be a removable medium or a medium that is fixedly installed in an apparatus or device, such as for instance the mobile phone 400 of Fig. 4.

Fig. 10 shows an illustration of a simulation set-up for testing the accuracy of position estimation according to an exemplary embodiment of the method according to the first aspect of the present invention.

Therein, it is assumed that the mobile terminal, which is in this case a Wideband Code Division Multiple Access (WCDMA) receiver, is arranged in a vehicle moving at a velocity of 20 m/s (about 72 km/h) along the trajectory depicted in Fig. 10. For position and velocity determination, a GPS receiver is employed. The stationary emitter is positioned at a latitude of 1000 m and a longitude of 1000 m. In Fig. 10, the position of the stationary emitter is marked by the rectangle.

It is further assumed that all measurements, i.e. the position of the mobile terminal, the velocity of the mobile terminal and the value indicative of the Doppler shift of the radio signal observed at the mobile terminal are Gaussian distributed around the true value and that they are independent of each other. The standard deviation of both the determined latitude (latitude error) and the determined longitude (longitude error) is assumed to be 60 m, while the standard deviation of the determined velocity is assumed to be 1.5 m/s. The standard deviation of the velocity determined based on the Doppler shift ( V_i in equation (7) ) is also assumed to be 1.5 m/s . Further, its is assumed that the error made in determining the Doppler shift of the radio signal observed at the WDCMA receiver is in the order of 5 % to 10 %, i.e. in determining the velocity of the mobile terminal based on the Doppler shift in the worst case an error of 5 km/h is made if the mobile terminal moves in fact at a velocity of 50 km/h. The standard deviation of the thus obtained velocity is assumed to be half of the maximum error, which is a relatively conservative assumption. Experiments have shown that the above assumptions are reasonable.

According to the simulation set-up, 41 sets of data are obtained. The points in time for which values of the parameters of the sets of data are determined are chosen to correspond to regularly spaced positions of the mobile terminal along the y-axis (vertical axis) in Fig. 10. This corresponds to roughly determining a set of data every second. Fig. 11 shows a probability distribution describing the estimated position obtained in the simulation according to Fig. 10.

The mean of the depicted probability distribution is located at the position (981 m, 997 m) , the standard deviation is 16 m in the first dimension and 9.9 in the second dimension.

Furthermore, it is readily clear for a person skilled in the art that the logical blocks in the schematic block diagrams as well as the flowchart and algorithm steps presented in the above description may at least partially be implemented in electronic hardware and/or computer software, wherein it may depend on the functionality of the logical block, flowchart step and algorithm step and on design constraints imposed on the respective devices to which degree a logical block, a flowchart step or algorithm step is implemented in hardware or software. The presented logical blocks, flowchart steps and algorithm steps may for instance be implemented in one or more digital signal processors (DSPs) , application specific integrated circuits (ASICs) , field programmable gate arrays (FPGAs) or other programmable devices. The computer software may be stored in a variety of

computer-readable storage media of electric, magnetic, electro-magnetic or optic type and may be read and executed by a processor, such as for instance a microprocessor. To this end, the processor and the storage medium may be coupled to interchange information, or the storage medium may be included in the processor.

The invention has been described above by means of

embodiments, which shall be understood to be exemplary and non-limiting. In particular, it should be noted that there are alternative ways and variations which are obvious to a skilled person in the art and can be implemented without deviating from the scope and spirit of the appended claims.

Claims

1. A method, comprising:

determining for a point in time a position and a velocity of a moving mobile terminal using a navigation system; determining for the point in time a value indicative of a Doppler shift of a radio signal observed at the mobile terminal, the radio signal being emitted by a stationary emitter; and

estimating the position of the stationary emitter based on the determined position of the mobile terminal, the determined velocity of the mobile terminal and the determined value indicative of the Doppler shift of the radio signal observed at the mobile terminal.

2. The method of claim 1, comprising at least one of: determining the position and the velocity of the mobile terminal for the point in time using navigation system navigation capabilities of the mobile terminal; and determining at the mobile terminal the value indicative of the Doppler shift of the radio signal observed at the mobile terminal.

3. The method according to any of the claims 1-2, wherein the mobile terminal is a mobile communication terminal, the stationary emitter is a stationary communication node and wherein the radio signal is a carrier wave for communication between the stationary communication node and the mobile communication terminal.

The method according to any of the claims 1-3, wherein for estimating the position of the stationary emitter at least two sets of data are determined and wherein one of the following conditions is met:

the first set of data is associated with a first point in time and the second set of data is associated with a second point in time, each set of data comprising for the respective point in time a determined position of the mobile terminal, a determined velocity of the mobile terminal and a determined value indicative of a Doppler shift of the radio signal observed at the mobile terminal; and

the first set of data is related to a first mobile terminal and the second set of data is related to a second mobile terminal, each set of data comprising for a point in time a determined position of the respective mobile terminal, a determined velocity of the respective mobile terminal and a determined value indicative of a Doppler shift of the radio signal observed at the respective mobile terminal.

The method of claim 4, wherein estimating the position of the stationary emitter comprises performing triangulation based on:

the relative direction of the stationary emitter with respect to the determined position of the mobile terminal derived from the first set of data, and the relative direction of the stationary emitter with respect to the determined position of the mobile terminal derived from the second set of data.

6. The method according to any of the claims 1-5, wherein estimating the position of the stationary emitter comprises determining for the point in time the distance between the mobile terminal and the stationary emitter based on at least one of:

the propagation delay of the radio signal emitted by the stationary emitter and

the path loss of the radio signal emitted by the stationary emitter.

7. The method according to any of the claims 1-6, wherein estimating the position of the stationary emitter is performed at the mobile terminal.

8. The method according to any of the claims 1-7, wherein the method comprises determining reliability

information regarding the estimated position of the stationary emitter.

9. The method according to any of the claims 1-8, comprising at least one of the following:

transmitting the estimated position of the stationary emitter to a server;

transmitting the determined position of the mobile terminal, the determined velocity of the mobile terminal, the determined value indicative of the Doppler shift of the radio signal observed at the mobile terminal and at least one of

the determined propagation delay of the radio signal emitted by the stationary emitter, the determined path loss of the radio signal emitted by the stationary emitter, and the determined distance between the determined position of the mobile terminal and the stationary emitter

to a server and estimating at the server the position of the stationary emitter based on the transmitted values; and

determining at least two sets of data, wherein one of the following conditions is met:

the first set of data is associated with a first point in time and the second set of data is associated with a second point in time, each set of data comprising for the respective point in time a determined position of the mobile terminal, a determined velocity of the mobile terminal and a determined value indicative of a Doppler shift of the radio signal observed at the mobile terminal, the first set of data is related to a first mobile terminal and the second set of data is related to a second mobile terminal, each set of data comprising for a point in time a determined position of the respective mobile terminal, a determined velocity of the respective mobile terminal and a determined value indicative of a Doppler shift of the radio signal observed at the respective mobile terminal ,

transmitting the at least two sets of data to a server and estimating at the server the position of the stationary emitter based on the transmitted sets of data .

The method according to claim 9, comprising: transmitting an identifier identifying the stationary emitter from the stationary emitter to the mobile terminal ;

transmitting the identifier from the mobile terminal to the server.

11. The method according to claim 10, comprising:

transmitting an identifier identifying a stationary emitter from the mobile terminal to the server;

retrieving at the server the estimated position of the stationary emitter based on the transmitted identifier; and

transmitting the retrieved estimated position of the stationary emitter to the mobile terminal having transmitted the identifier.

12. The method according to any of the claims 1-11, wherein estimating the position of the stationary emitter is only performed if the determined velocity of the mobile terminal reaches at least a predetermined threshold velocity .

13. The method according claim 12, wherein the predetermined threshold velocity is chosen from a range between 1 m/s and 2 m/s .

14. An apparatus, comprising means for performing the method of any of claims 1-13.

15. An apparatus, comprising: a navigation system navigation module configured to determine for a point in time a position and a velocity of a moving mobile terminal; and

a frequency analyzer configured to determine for the point in time a value indicative of a Doppler shift of a radio signal observed at the mobile terminal, the radio signal being emitted by a stationary emitter;

wherein

the navigation system navigation module is configured to provide the determined position of the mobile terminal and the determined velocity of the mobile terminal to a position estimator; the frequency analyzer is configured to provide the determined value indicative of the Doppler shift of the radio signal observed at the mobile terminal to the position estimator;

the position estimator is configured to estimate the position of the stationary emitter based on the determined position of the mobile terminal, the determined velocity of the mobile terminal and on the determined value indicative of the Doppler shift of the radio signal observed at the mobile terminal .

The apparatus according to claim 15, wherein at least one of the following conditions is met:

the navigation system navigation module forms part of the mobile terminal; and

the frequency analyzer forms part of the mobile terminal .

17. The apparatus according to any of claims 15-16, wherein the mobile terminal is a mobile communication terminal, the stationary emitter is a stationary communication node and wherein the radio signal is a carrier wave for communication between the stationary communication node and the mobile communication terminal.

18. The apparatus according to any of claims 15-17, wherein for estimating the position of the stationary emitter at least two sets of data are determined and wherein one of the following conditions is met:

19. The apparatus according to claim 18, wherein the

position estimator is configured to estimate the position of the stationary emitter by performing triangulation based on: the relative direction of the stationary emitter with respect to the determined position of the mobile terminal derived from the first set of data, and the relative direction of the stationary emitter with respect to the determined position of the mobile terminal derived from the second set of data.

20. The apparatus according to any of claims 15-19, wherein the apparatus comprises a distance estimator configured to determine for the point in time the distance between the mobile terminal and the stationary emitter based on at least one of:

the propagation delay of the radio signal emitted by the stationary emitter and

the path loss of the radio signal emitted by the stationary emitter

and wherein the position estimator is configured to also base estimating the position of the stationary emitter on the determined distance.

21. The apparatus according to any of claims 15-20, wherein the position estimator forms part of the mobile terminal .

22. The apparatus according to any of the claims 15-21, wherein the position estimator is configured to determine reliability information regarding the estimated position of the stationary emitter.

The apparatus according to any of claims 15-22, wherein at least one of the following conditions is met: the apparatus comprises a transmitter configured to transmit the estimated position of the stationary emitter to a server;

the apparatus comprises a transmitter configured to transmit the determined position of the mobile terminal, the determined velocity of the mobile terminal, the determined value indicative of the Doppler shift of the radio signal observed at the mobile terminal and at least one of

the determined propagation delay of the radio signal emitted by the stationary emitter, the determined path loss of the radio signal emitted by the stationary emitter, and

the determined distance between the determined position of the mobile terminal and the stationary emitter

to a server, the server comprising a position estimator configured to estimate the position of the stationary emitter based on the transmitted values; and

at least two sets of data are determined, wherein one of the following conditions is met:

the apparatus comprises a transmitter configured to transmit the at least two sets of data to a server, the server comprising a position estimator configured to estimate the position of the stationary emitter based on the transmitted sets of data.

24. The apparatus according to claim 23, wherein:

the stationary emitter is configured to transmit an identifier identifying the stationary emitter from the stationary emitter to the mobile terminal;

the mobile terminal comprises a transmitter configured to transmit the identifier from the mobile terminal to the server.

25. The apparatus according to claim 24, wherein:

the mobile terminal comprises a transmitter configured to transmit an identifier identifying a stationary emitter from the mobile terminal to the server;

the server is configured to retrieve the estimated position of the stationary emitter based on the transmitted identifier; and

the server comprises a transmitter configured to transmit the retrieved estimated position of the stationary emitter to the mobile terminal having transmitted the identifier.

26. The apparatus according to any of claims 15-25, wherein the position estimator is configured to perform estimating the position of the stationary emitter only if the determined velocity of the mobile terminal reaches at least a predetermined threshold velocity.

27. The apparatus according to claim 26, wherein the

predetermined threshold velocity is chosen from a range between 1 m/s and 2 m/s .

28. The apparatus according to any of claims 15-27, the apparatus being a mobile phone further comprising: user interface circuitry and user interface software configured to facilitate user control of at least some functions of the mobile phone through use of a display and configured to respond to user inputs and

a display and display circuitry configured to display at least a portion of a user interface of the mobile phone, the display and display circuitry configured to facilitate user control of at least some functions of the mobile phone.

29. An apparatus, comprising:

means for determining for a point in time a position and a velocity of a moving mobile terminal;

means for determining for the point in time a value indicative of a Doppler shift of a radio signal observed at the mobile terminal, the radio signal being emitted by a stationary emitter;

means for providing the determined position and the determined velocity to means for estimating the position of the stationary emitter allocated to the means for determining for a point in time a position and a velocity of a moving mobile terminal;

means for providing the determined value indicative of the Doppler shift of the radio signal observed at the mobile terminal to the means for estimating the position of the stationary emitter allocated to the means for determining for the point in time a value indicative of a Doppler shift of a radio signal observed at the mobile terminal ;

wherein the means for estimating the position of the stationary emitter comprise means for estimating the position of the stationary emitter based on the determined position of the mobile terminal, the determined velocity of the mobile terminal and on the determined value indicative of the Doppler shift of the radio signal observed at the mobile terminal.

An apparatus, comprising a position estimator

configured to estimate the position of a stationary emitter emitting a radio signal based on:

a position of a moving mobile terminal determined for a point in time, the determined position of the mobile terminal being provided by a navigation system navigation module configured to determine a position of the mobile terminal for the point in time;

a velocity of the mobile terminal determined for the point in time, the determined velocity of the mobile terminal being provided by the navigation system navigation module which is further configured to determine the velocity of the mobile terminal for the point in time; and a value indicative of a Doppler shift of a radio signal observed at the mobile terminal determined for the point in time, the radio signal being emitted by the stationary emitter and the determined value indicative of the Doppler shift of the radio signal observed at the mobile terminal being provided by a frequency analyzer configured to determine for the point in time the value indicative of the Doppler shift of the radio signal observed at the mobile terminal.

An apparatus, comprising means for estimating the position of stationary emitter emitting a radio signal based on:

a position of a moving mobile terminal determined for a point in time, the determined position of the mobile terminal being provided by means for determining for the point in time a position and a velocity of the moving mobile terminal;

a velocity of the moving mobile terminal determined for the point in time, the determined velocity of the mobile terminal being provided by the means for determining for the point in time a position and the velocity of the moving mobile terminal; and

a value indicative of a Doppler shift of a radio signal observed at the mobile terminal determined for the point in time, the radio signal being emitted by the stationary emitter and the determined value indicative of the Doppler shift of the radio signal observed at the mobile terminal being provided by means for determining for the point in time the value indicative of the Doppler shift of the radio signal observed at the mobile terminal.

32. A system, comprising:

a navigation system navigation module configured to determine for a point in time a position and a velocity of a moving mobile terminal;

a frequency analyzer configured to determine for the point in time a value indicative of a Doppler shift of a radio signal observed at the mobile terminal, the radio signal being emitted by a stationary emitter; and a position estimator configured to estimate the position of the stationary emitter based on the determined position of the mobile terminal, the determined velocity of the mobile terminal and on the determined value indicative of the Doppler shift of the radio signal observed at the mobile terminal.

33. A system, comprising:

means for determining for the point in time a value indicative of a Doppler shift of a radio signal observed at the mobile terminal, the radio signal being emitted by a stationary emitter; and

means for estimating the position of the stationary emitter based on the determined position of the mobile terminal, the determined velocity of the mobile terminal and on the determined value indicative of the Doppler shift of the radio signal observed at the mobile terminal .

34. A program comprising: program code for performing the method according to any of the claims 1-14 when the program is executed on a processor .

A readable medium having a program according to claim 34 stored thereon.