DE102006059623B3 - Method and system for position determination - Google Patents

Abstract

It is an object of the present invention to provide a method and a system for autonomous, and with respect to the transmitter, contactless position determination of a receiver, with an accurate position determination using low-cost receiver and as few transmitters should be ensured, especially in areas where GPS signals are not available. The inventive method comprises the following method steps: emission of electromagnetic radiation of a first transmission frequency (f <SUB> 1 </ SUB>) by means of the first transmitter (1), wherein the first transmission frequency (f <SUB> 1 </ SUB>) with a first modulation frequency (f <SUB> M1 </ SUB>) is modulated; Emitting electromagnetic radiation of a second transmission frequency (f <SUB> 2 </ SUB>) by means of the second transmitter (2), the second transmission frequency (f <SUB> 2 </ SUB>) having a second modulation frequency (f <SUB> M2 </ SUB>), and wherein the first frequency (f <SUB> 1 </ SUB>) differs from the second frequency (f <SUB> 2 </ SUB>) such that there is a beat with a beat frequency (f <SUB> S </ SUB>) forms; Measuring at least a first amplitude (A <SUB> 1 </ SUB>) of the beat frequency (f <SUB> S </ SUB>) from a first point in time (t <SUB> 1 </ SUB>) (4); Measuring at least one second amplitude (A <SUB> 2 </ SUB>) of the beat frequency (f <SUB> S </ SUB>) from a second time (t <SUB> 2 </ SUB>) at a second position (x <SUB> 2 </ SUB>) of the receiver (4); and determining the second position (x <SUB> 2 </ SUB>) of the receiver (4) with respect to the first position (x <SUB> 1 </ SUB>) of the receiver (4) from the ...

Description

The The present invention relates to a method and a system for Position determination with the features mentioned in claims 1 and 31. Especially The present invention relates to a method for localization a recipient in an environment in which conventional Positioning systems, such as GPS, are not available.

In many areas, for example in vehicle navigation the positioning of a person or an object of elementary meaning. In particular for contactless position determination powerful systems nowadays, such as the Global Positioning System (GPS). GPS based on satellites that are constantly their changing Emit position and the exact time. From their signal transit time can GPS receivers then calculate their own position and speed. Basically enough the signals from three satellites. In practice, however, have GPS receiver no clock that is accurate enough to calculate the run times correctly to be able to. Therefore, the signal of a fourth satellite is needed.

Disadvantageously GPS is only applicable in areas where a GPS receiver is the sufficient from the (at least) four satellites emitted signals good reception. However, such a situation is in many areas, in which a position determination is necessary, not given. To counting For example, vehicle tunnels in which the vehicle position for Navigation should be determined. Often you can get GPS signals not received within vehicle tunnels. A location of the vehicle can only be realized after leaving the tunnel by GPS, which is particularly disadvantageous if several within the tunnel Driving directions are available, between which the navigation system must distinguish.

One Another example is a grain silo, within which GPS signals can not be received well enough. An existing within the grain elevator Work machine whose position is monitored should, could do not resort to GPS positioning, so here's alternative activities must be taken.

Should a contactless, independent Positioning of a person or an object (each via a have suitable receivers) in Areas of insufficiently strong GPS signals, It is known to use electromagnetic signals that are local Broadcasters are broadcast. From the phase shift of the receiver received signal (provided that the transmitter is stationary are) on the relative movement of the receiver, whose position is determined should be closed to one of the channels. This must be the Phase shift of the receiver be determined to the transmitter. A disadvantage here is that the phase shift between transmitter and receiver can only be determined if either both transmitter and Receiver via synchronous, high-precision Have clocks or an additional one Reference signal is taken to help. However, this requires accordingly expensive technical components.

Out EP 47 561 A1 For example, a method for determining the location of a mobile object by means of radio signals transmitted by at least two fixed transmitting stations is known. The localization is based on the transit time of the time difference of a zero crossing at two different locations.

It is therefore an object of the present invention, a method and a system for independent, and in terms of transmitters, contactless positioning of a receiver indicate using an exact position determination cheap receiver and as possible less transmitter guaranteed should be, especially in areas where GPS signals are not available are. Furthermore, it should be based on the use of reference signals or high-precision, synchronous watches or similar Time measuring devices can be dispensed with.

These The object is achieved by the features in claim 1 (method claim) and in the claim 31 (device claim) Advantageous embodiments The invention are contained in the subclaims.

One particular advantage of the invention is that with inexpensive Senders and receivers the position of a recipient also in (for GPS signals) hard to reach Areas, can be determined accurately and quickly. In a preferred variant only 2 transmitters and one receiver are needed. Therefore, this is suitable inventive system for example, as a supplement for GPS receivers in Areas of weak or nonexistent GPS signals, the corresponding from the system according to the invention Receiving transmitted signals, and so their position in the field of Sender can determine alternatively to the GPS. This will be a good one Alternative or supplement for GPS positioning created.

• – Aussenden elektromagnetischer Strahlung einer erste Sendefrequenz mittels eines ersten Senders, wobei die erste Sendefrequenz mit einer ersten Modulationsfrequenz moduliert wird,
• – Aussenden elektromagnetischer Strahlung einer zweiten Sendefrequenz mittels eines zweiten Senders, wobei die zweite Sendefrequenz mittels einer zweiten Modulationsfrequenz moduliert wird, und wobei die erste Sendefrequenz und die zweite Sendefrequenz derart gewählt werden, dass sich eine (niederfrequente) Schwebung (mit einer Schwebungsfrequenz f_S) ausbildet,
• – Messen mindestens einer ersten Amplitude der Schwebungsfrequenz ab einem ersten Zeitpunkt an einer ersten Position des Empfängers und
• – Messen mindestens einer zweiten Amplitude der Schwebungsfrequenz ab einem zweiten, später folgenden Zeitpunkt an einer zweiten Position des Empfängers und
• – Ermitteln der zweiten Position des Empfängers in Bezug auf die erste Position aus der mindestens ersten und zweiten gemessenen Amplitude der Schwebungsfrequenz.

The inventive method for Be Determining the position of a movable receiver has the following method steps:

• Emitting electromagnetic radiation of a first transmission frequency by means of a first transmitter, wherein the first transmission frequency is modulated with a first modulation frequency,
• Emitting electromagnetic radiation of a second transmission frequency by means of a second transmitter, wherein the second transmission frequency is modulated by means of a second modulation frequency, and wherein the first transmission frequency and the second transmission frequency are selected such that a (low-frequency) beat (with a beat frequency f _S ) forms,
• - Measuring at least a first amplitude of the beat frequency from a first time at a first position of the receiver and
• - Measuring at least a second amplitude of the beat frequency from a second, later following time at a second position of the receiver and
• Determining the second position of the receiver with respect to the first position from the at least first and second measured amplitude of the beat frequency.

The idea of the invention is therefore that a modulation of the carrier frequencies (first and second transmission frequency) leads to a beat, which in addition to a maximum (beat) amplitude also has additional secondary maxima whose amplitude is phase-dependent. Therefore, the phase shift of the beat and thus the relative movement of the receiver between the first time and the second time can be reconstructed by simple amplitude measurement of the low-frequency beat signal. For this purpose, it is provided that at least one secondary maximum of the modulated beat frequency determined and from this amplitude value, the phase shift of the receiver relative to the at least two transmitters and thus the relative movement of the receiver during the corresponding time interval (t ₂ - t ₁ ) can be determined. Free transmission frequencies are preferably used as first and second transmission frequencies. According to the invention, it is provided that a moving receiver continuously measures the amplitudes of the beat frequency and continuously determines its relative movement and thus its position from the change in these amplitudes, preferably from the change in the amplitudes of the secondary maxima. If the receiver is aware of its initial absolute position (for example, by receiving a GPS signal), the receiver can now continue to determine the absolute position continuously by determining its relative position at an initially known absolute position. It is particularly preferred to select the transmission and modulation frequencies in such a way that the beat signal (per period) has, in addition to a global main maximum, at least one secondary maximum (preferably between 2 and 5 secondary maxima).

One particular advantage of the present invention is that only the amplitude of the low-frequency beat signal measured and from this already the relative movement of the receiver between the two transmitters can be determined. The use of a reference signal or a high synchronous clock is not necessary. For example, the stations within a tunnel, it would be possible to position one Tunnel passing through car (even if not receiving a GPS signal) high-precision and very cheap to determine.

Preferably the at least two transmitters are spatially constant and stationary arranged to each other. Preferably, the first and second modulation frequencies each a whole multiple or a part of the beat frequency (The first and second modulation frequencies differ in each case from the beat frequency). Furthermore, it is preferable to measure the amplitude of the beat signal by the receiver with perform such a high (sampling) frequency and evaluate that the receiver within a measuring interval at most by the amount λ / 2 (half wavelength the beat frequency). That's the way it is, for example for the Position determination of motor vehicles possible, the highest possible speed for motor vehicles (for example, 500 km / h) and the minimum scan period, with which the amplitude of the beat frequency has to be measured, to determine accordingly. Because of the amplitude of the beat frequency a phase shift is detected, it is necessary that the moving receiver within a scan period at most a distance of λ / 2 (corresponds to a phase shift of Pi) has covered.

Preferably are the first and second transmission frequencies, the first and second modulation frequencies and consequently the beat frequency is constant. It continues preferred that the first modulation frequency equal to the second Modulation frequency selected becomes. By suitable choice of the transmission and modulation frequencies (and thus the beat frequency) leads the phase shift of the receiver (due to its movement between the channels) to a special strong variation of the amplitude of the beat frequency (in particular the at least one secondary maximum), so that a particularly trouble-free Position determination or the use of particularly inexpensive technical Components (transmitter and receiver) is possible.

Preferably the beat frequency is in a range between 10 MHz and 100 MHz set. In the aforementioned embodiments, in which two transmitters are available the position of the recipient and thus the movement of the recipient Determine exactly along the connecting line of the two transmitters.

Should the position of a recipient not determined along a line, but within a plane be, it is provided according to the invention that in each case a first, a second and a third transmitter electromagnetic Emitting radiation having a first, second and third transmission frequency, wherein the first transmission frequency having a first modulation frequency, the second transmission frequency with a second modulation frequency and the third transmission frequency modulated with a third modulation frequency and wherein the first, second and third transmission frequencies respectively differ so that one (low frequency) beat forms and wherein the amplitude of the low-frequency beat frequency is measured at different times and from the amplitude the beat frequency (in particular from the amplitude of at least a secondary maximum) at different times the relative movement Recipient is determined within the appropriate time interval. The above made statements to preferred frequencies and the features of the claims 2-22 for this embodiment apply analogously. For one spatial (Three-dimensional) position determination, the system can also four or more channels are extended.

The Requirements for the recipient However, do not rise, since this only the amplitude of the low-frequency Beat frequency must measure and from this its position (over the Relative movement). It is preferably provided that the transmission frequencies and the modulation frequencies are standardized. Then the receiver after measuring the amplitudes at different times automatically by corresponding mathematical transformations determine its relative position. The computational effort obviously increases with the number of transmitters. It is preferably provided that the receiver has a corresponding data processing device, which consists of the first and second transmission frequencies, the first and second transmission frequencies second modulation frequency and the at least two measured amplitudes the relative movement determined by calculation. Alternatively, it may be provided be that the receiver has a Has data table, from which he measured the corresponding amplitude value pairs Can take relative position.

alternative but it is also possible that the inventive system for position determination depending on the application with different (also time-variable) transmission and modulation frequencies works and the stations possibly at different intervals are positioned to each other or positioned. Then it is provided according to the invention at least one of the transmitters has data corresponding to the receiver via the Transmit and modulate sequences, so the receiver then by means of a data processing device and the transmitted Data after measurement of amplitude pairs its relative motion automatically calculated can determine.

The The invention will be explained in more detail with reference to embodiments.

It demonstrate:

1 the system for position determination according to the invention in a schematic representation,

2a the beat signal measured by a receiver at a first location, provided that the first and second transmission frequencies have not been modulated (prior art),

2 B the beat signal measured by a receiver at a second location, wherein the transmission frequencies have not been modulated (prior art),

3a the beating signal measured by a receiver at a first location according to the invention when both the first and second transmissions have been modulated,

3b the beating signal measured by a receiver according to the invention at a second location which is opposite to the first location ( 3a ) is shifted,

4a the beating signal measured by a receiver according to the invention at a first location, which was generated by means of three transmitters, and

4b the beat signal measured by a transmitter at a second location according to the invention.

1 shows a schematic representation of the system according to the invention. This system according to the invention consists of a first transmitter 1 and a second transmitter 2 , The first station 1 transmits electromagnetic radiation having a first transmission frequency f ₁ and the second transmitter 2 according to electromagnetic radiation with egg ner second frequency f ₂ . The transmission frequencies f ₁ and f ₂ are selected such that a beat frequency f _S , preferably between 0.1 MHz and 100 MHz is formed. According to the invention, the transmitter 1 . 2 with the modulator 3 connected, which modulates the transmission frequencies f ₁ and f ₂ each with a modulation frequency f _M1 and f _M2 . The modulation frequencies are preferably an integral multiple or a whole part of the beat frequency. The modulator 3 modulates the transmission frequencies f ₁ and f _{2 of} the transmitters 1 . 2 corresponding.

The recipient 4 that is between the transmitters 1 . 2 moved, can now determine its position independently and contactless. A particular advantage is that the transmitter 4 has neither a highly synchronous clock, nor a reference signal must have. Furthermore, the receiver 4 be made inexpensively, since it only has to be suitable for measuring the amplitude of the low-frequency beat signal. From successive measurements of the amplitude of the beat signal, the receiver 4 always its relative position and thus in the course of several measurements its movement between the transmitters 1 . 2 determine. Is the receiver 4 his initial, absolute position between the stations 1 . 2 As is known, it can also calculate its absolute position continuously from its relative movement.

The inventive determination of the position of the receiver 4 will be explained in more detail below.

2a shows a beat signal according to the prior art. Such a beat signal would be the receiver 4 received, for example, if the leading to beat transmission frequencies f ₁ , f _{2 would} not be modulated. Although it would affect the movement of the recipient 4 its relative position to the transmitters 1 . 2 change and thus take place a phase shift of the received beat signal (see 2 B ), however, in the case of non-modulated transmission frequencies (as in the 2a . 2 B ) determine its relative movement only if it were synchronized with the transmitters or received a reference signal from at least one transmitter. However, this would make correspondingly higher demands on the transmitter and the receiver, so that the corresponding method would be significantly more complex. Another disadvantage would be an increased susceptibility to failure of such a system.

However, if the transmission frequencies f ₁ and f _{2 are} modulated according to the invention (see 3a ), is also the beat image, that of the receiver 4 received beat frequency in their intensity (amplitude) modulated. The beat amplitude measured by the receiver points, as in 3a Obviously, one main maximum and two secondary maxima. In the present embodiment, the transmitter frequencies f ₁ = 16.07 MHz and f ₂ = 15.76 MHz. The resulting beat frequency is f _S = 0.32 MHz and the modulation frequencies are f _M1 = f _M2 = 0.16 MHz. The time values (the x-axes of the 2 - 4 ) are to be provided with the factor 10 ^-6 s.

The inventive idea is that the modulation image of the beat changes very much (see 3b ) when the receiver 4 between the stations 1 . 2 moved, whereby a phase shift of the transmission signals is caused. Such a phase shift leads to a change in the amplitude of the secondary maxima (of the at least one secondary maximum). The recipient 4 can now determine the amplitude of the at least one secondary maximum and calculate very simply its relative displacement. For this, however, it is necessary for the receiver to know all the transmission and modulation frequencies in addition to the at least two amplitude values. In 3b the receiver was exactly between the transmitters 1 . 2 ; in comparison, the relative displacement of the receiver is 4 (in 3a ) approximately Δx = 3 mm.

If these are always constant, it is also possible, for example, to process the amplitude value pairs into a data table with correspondingly correlated relative displacements, so that the receiver can take its relative movement from a corresponding data table after measurement of successive amplitudes of the at least one secondary maximum. It is therefore provided according to the invention, on the one hand to set the transmission frequencies f ₁ and f ₂ such that forms a beat and on the other hand to select the modulation frequencies such that the forming beating at least one secondary maximum (whose amplitude is phase-dependent).

A recalculation the relative movement of the transmission and modulation frequencies can in a simple way by means of known mathematical algorithms be made. For predetermined transmission and modulation frequencies, the amplitude the beat frequency in dependence the phase shift (ie the relative movement) by appropriate calculated mathematical superposition of the modulated transmission frequencies become. The dissolution the corresponding equations after the phase shift or The relative movement can then be explicitly or numerically with the aid of corresponding computer programs, such as Mathematica, be made.

The 4a and 4b show another off guiding example according to the present invention. In the embodiment, three spaced apart transmitters were used, each transmitting at respective transmission frequencies to form a beat sequence. The modulation frequencies of the individual transmitters were set such that the beat frequency has four additional secondary maxima in addition to the main maximum. How out 4a can be seen, the beat image for an initial phase (first position of the transmitter - see 4a ) has a characteristic beat image in which obviously the secondary maximum lying to the left of the main maximum has a significantly higher amplitude than the remaining secondary maxima. Now moves the receiver 4 relative to the three transmitters (and thereby reaches the second position - see 4b ), this leads to a phase shift, which leads to a change in the amplitude of the secondary maxima. In particular, it can be seen that the secondary maximum lying to the left of the main maximum is one compared to 4a has significantly reduced amplitude. From the change in the amplitudes of the secondary maxima can now in the manner described above on the position (relative movement) of the receiver 4 getting closed.

1

first transmitter

2

second transmitter

3

modulator

4

receiver

Claims (32)

Method for determining the position of a mobile receiver ( 4 ), whereby at least two transmitters ( 1 . 2 ), with the following method steps: emitting electromagnetic radiation of a first transmission frequency (f ₁ ) by means of the first transmitter ( 1 ), wherein the first transmission frequency (f ₁ ) is modulated with a first modulation frequency (f _M1 ), - emission of electromagnetic radiation of a second transmission frequency (f ₂ ) by means of the second transmitter ( 2 ), wherein the second transmission frequency (f ₂ ) is modulated with a second modulation frequency (f _M2 ), and wherein the first frequency (f ₁ ) differs from the second frequency (f ₂ ) such that a beat with a beat frequency (f ₂ ) f _S ), measuring at least one first amplitude (A ₁ ) of the beat frequency (f _S ) from a first instant (t ₁ ) on a first position (x ₁ ) of the receiver ( 4 Measuring at least one second amplitude (A ₂ ) of the beat frequency (f _S ) from a second instant (t ₂ ) on a second position (x ₂ ) of the receiver ( 4 ), and - determination of the second position (x ₂ ) of the receiver ( 4 ) with respect to the first position (x ₁ ) of the recipient ( 4 ) from the at least one first amplitude (A ₁ ) and the at least one second amplitude (A ₂ ) of the beat frequency (f _S ). Method according to claim 1, characterized in that the at least two transmitters ( 1 . 2 ) are arranged in a spatially constant distance from each other. Method according to one of the preceding claims, characterized in that the at least two transmitters ( 1 . 2 ) are arranged stationary. Method according to one of the preceding claims, characterized in that the first and second modulation frequency (f _M1 , f _M2 ) each differ from the beat frequency (f _S ). Method according to one of the preceding claims, characterized in that the first modulation frequency (f _M1 ) is a whole multiple of the beat frequency (f _S ) or the beat frequency (f _S ) is a whole multiple of the first modulation frequency (f _M1 ). Method according to one of the preceding claims, characterized in that the second modulation frequency (f _M2 ) is a whole multiple of the beat frequency (f _S ) or the beat frequency (f _S ) is a whole multiple of the second modulation frequency (f _M2 ). Method according to one of the preceding claims, characterized in that the determination of the position of the receiver ( 4 ) is carried out continuously, wherein in each case after the position determination, the determined position (x ₂ ) of the receiver ( 4 ) as a new, known position of the recipient ( 4 ) for determining the position (x ₃ ) of the receiver ( 4 ) is used at a later time (t ₃ ). Method according to one of the preceding claims, characterized in that the absolute position data of the receiver ( 4 ) continuously from the continuously measured amplitude values (A ₁ , A ₂ ) of the beat frequency (f _S ) as well as from the initially known, absolute position data (x ₁ ) of the receiver ( 4 ). Method according to one of the preceding claims, characterized in that the first transmission frequency (f ₁ ) is greater than the second transmission frequency (f ₂ ). Method according to claim 15, characterized in that the condition: 1,2 · f2> f 1 > f 2 is satisfied, where f _{1 is} the first transmission frequency and f _{2 is} the second transmission frequency. A method according to claim 16, characterized in that the condition: 1.1 · f ₂ > f ₁ > f _{2 is} satisfied. A method according to claim 17, characterized in that the condition: 1.05 · f ₂ > f ₁ > 1.01 · f _{2 is} satisfied. Method according to one of the preceding claims, characterized in that the first transmission frequency (f ₁ ) and the second transmission frequency (f ₂ ) are selected from the range between 100 MHz and 2 GHz. Method according to one of the preceding claims, characterized in that the first transmission frequency (f ₁ ) and the second transmission frequency (f ₂ ) are selected such that the difference between the first transmission frequency (f ₁ ) and second transmission frequency (f ₂ ) in the range of 10 MHz to 100 MHz. Method according to one of the preceding claims, characterized in that the receiver ( 4 ) along the connecting line between the first transmitter ( 1 ) and the second transmitter ( 2 ) emotional. Method according to one of the preceding claims, characterized in that the relative movement of the receiver ( 4 ) during successive measuring times along the connecting line between the first transmitter ( 1 ) and the second transmitter ( 2 ) is determined. Method according to one of the preceding claims, thereby marked that additionally at least a third transmitter is provided, wherein the first transmitter, the second transmitter and the third transmitter are each spaced from each other being, in addition electromagnetic radiation of a third transmission frequency by means of third transmitter is transmitted, and the third transmission frequency with a third modulation frequency is modulated and where each of the first, second and third transmission frequencies in such a way from each other differ that a beat with a beat frequency formed. Method according to claim 23, characterized in that the receiver ( 4 ) is moved in the plane spanned by the first transmitter, second transmitter and third transmitter. Method according to one of claims 23 and 24, characterized in that the relative movement of the receiver ( 4 ) is determined during successive measurement times along the plane spanned by the first transmitter, the second transmitter and the third transmitter. Method according to one of Claims 23 and 24, characterized in that, within a first time interval (I ₁ ), the first and second transmitters transmit with their respectively modulated transmission frequency, the third transmitter does not transmit within a first time interval (I ₁ ), and within a second time interval (I ₂ ) the first and third transmitters transmit with their respectively modulated transmit frequency, wherein the second transmitter does not transmit within a second time interval (I ₂ ), and wherein within the first time interval (I ₁ ) and the second time interval (I ₂ ) in each case at least two amplitudes of the beat frequency at respectively different points in time are measured and, from the amplitudes of the beat frequency measured during the first time interval (I ₁ ), a first relative movement of the receiver (FIG. 4 ) is determined along a first connecting line between the first transmitter and the second transmitter, and from the amplitudes of the beat frequency measured during the second time interval (I ₂ ) a second relative movement of the receiver (FIG. 4 ) is determined along a second connecting line between the first transmitter and the third transmitter, and from the first relative movement along a first connecting line and the second relative movement along a second connecting line the relative movement of the receiver ( 4 ) is determined along the plane spanned by the first transmitter, the second transmitter and the third transmitter. A method according to claim 26, characterized in that the first time intervals (I ₁ ) in which the first and the second transmitter transmit with their respective modulated transmission frequency and the third transmitter does not transmit, and the second time intervals (I ₂ ), in which the send the first and the third transmitter with their respective modulated transmission frequency and the second transmitter does not transmit, and alternate the relative movement of the receiver ( 4 ) is continuously determined along the plane defined by the first transmitter, the second transmitter and the third transmitter. Method according to one of claims 23 to 27, characterized in that the absolute position data of the receiver ( 4 ) continuously from the continuously determined relative movements of the receiver ( 4 ) along the spanned by first transmitter, second transmitter and third transmitter Level as well as the initially known, absolute position data of the recipient ( 4 ). Method according to one of the preceding claims, characterized in that to the receiver ( 4 ) via at least one of the transmitters ( 1 . 2 ) Data on the first transmission frequency (f ₁ ), the first modulation frequency (f _M1 ), the second transmission frequency (f ₂ ) and the second modulation frequency (f _M2 ) are transmitted. Method according to one of claims 23-29, characterized in that to the receiver ( 4 ) via at least one of the three transmitters data on the distances of at least two pairs of transmitters, the first transmission frequency, the first modulation frequency, the second transmission frequency, the second modulation frequency, the third transmission frequency and the third modulation frequency are transmitted. System for transmitting and receiving position data and for position determination, comprising: - a first transmitter ( 1 ) for emitting electromagnetic radiation of a first transmission frequency (f ₁ ), - a first modulator for modulating the first transmission frequency (f ₁ ) with a first modulation frequency (f _M1 ), - a second transmitter ( 2 ) for emitting electromagnetic radiation of a second transmission frequency (f ₂ ), - a second modulator for modulating the second transmission frequency (f ₂ ) with a second modulation frequency (f _M2 ), - wherein the first frequency (f ₁ ) of the second frequency ( f ₂ ) such that a beat with a beat frequency (f _S ) is formed, - means for measuring at least a first amplitude (A ₁ ) of the beat frequency (f _S ) from a first instant (t ₁ ) at a first position ( x ₁ ) of the recipient ( 4 ) Means for measuring at least a second amplitude (A ₂ ) of the beat frequency (f _S ) from a second instant (t ₂ ) at a second position (x ₂ ) of the receiver ( 4 ), and - means for determining the second position (x ₂ ) of the receiver ( 4 ) with respect to the first position (x ₁ ) of the at least one first amplitude (A ₁ ) and the at least one second amplitude (A ₂ ) of the beat frequency (f _S ). System according to claim 31, characterized in that the at least two transmitters ( 1 . 2 ) are arranged in a spatially constant distance from each other. System according to one of claims 31 and 32, characterized in that the at least two transmitters ( 1 . 2 ) are arranged stationary. System according to one of claims 31-33, characterized in that the first modulator and the second modulator are formed by a modulator connected to both the first transmitter ( 1 ) as well as with the second transmitter ( 2 ) connected is. The system of any of claims 31-34, comprising: - one third transmitter for emitting electromagnetic radiation third transmission frequency, - one third modulator for modulating the third transmission frequency with a third modulation frequency, - and where the first, the second and third transmission frequencies each differ from one another in such a way that a beat develops with a beat frequency. System according to claim 35, characterized in that the receiver ( 4 ) is arranged in the spanned by the first transmitter, second transmitter and third transmitter plane. System according to either of Claims 35 and 36, characterized in that means for periodically activating and deactivating the transmitters are such that, within a first time interval (I ₁ ), the first and second transmitters transmit at their respective modulated transmit frequencies and the third transmitters within one first time interval (I ₁ ) does not send, and that within a second time interval (I ₂ ) the first and the third transmitter transmit with their respective modulated transmission frequency and the second transmitter within a second time interval (I ₂ ) does not send. System according to claim 37, characterized in that the first time intervals (I ₁ ) and the second time intervals (I ₁ ) alternate periodically.