WO2014032698A1

WO2014032698A1 - Method and device for measuring weak inband interference

Info

Publication number: WO2014032698A1
Application number: PCT/EP2012/066661
Authority: WO
Inventors: Simon MECKEL; Heinz Mellein
Original assignee: Rohde & Schwarz Gmbh & Co. Kg
Priority date: 2012-08-28
Filing date: 2012-08-28
Publication date: 2014-03-06

Abstract

A measurement device for measuring a first input signal which is part of a measurement signal (31) comprises a measurement unit (28) set up for measuring the first input signal within a signal (37_1, ₂) derived from the measurement signal (31), a transformation unit (24) set up for transforming the measurement signal (31) or a signal (33_{1, 2}) derived from the measurement signal (31) into the frequency- domain resulting in a first frequency-domain signal (34₁), a filter unit (25) set up for removing components of the first frequency-domain signal (34₁) which correspond to a second input signal which is part of the measurement signal (31), resulting in a first filtered signal (35₁), and an inverse transformation unit (26) set up for transforming the first filtered signal (35₁) into the time-domain resulting in a first time- domain signal (361).

Description

Method and device for measuring weak inband interference The invention relates to a device and method for measuring a low power interference signal in the presence of an inband signal of greater power, preferably of a GPS

(Global Positioning System) signal. The continuous growth of mobile communication and

broadcast services makes frequency bands a highly demanded resource. The allocation of frequency bands to the

different services is tightly arranged. Especially the UHF band (0.3 - 3 GHz), in which the signal of the global satellite navigation system GPS (global positioning system) is transmitted, is very appropriate for mobile communication services. Ideally, signals transmitted on different frequencies do not interfere with each other. In reality however, the situation is more complex.

There has been an issue in the United States, where an LTE broadband signal, newly transmitted in an adjacent GPS frequency band, presumably interferes with the GPS signal. This causes wrong position determinations of wideband differential GPS receivers which are, amongst others, used in industrial farming machines like combine harvesters. These receivers allow very exact position determinations in the range of ±10 cm. Thus, the machines have the ability to almost operate autonomically without manual intervention. Wrong position determinations can cause significant economic loss or other kinds of damage in case of further automation of the machines. A preferred method of signal analysis is the examination of signals within the frequency-domain. Signals can often be identified by their characteristic shapes. If several signals interfere with each other, the spectral shape is changed which allows conclusions regarding the interferer. In case of very weak interfering signals, however, this method fails, since the interference signal is not visible within the noise present in the entire signal. The European Patent EP 1 592 131 Bl shows a spectrum analyzer capable of examining an input signal in the frequency-domain. As shown above, this spectrum analyzer is not capable of detecting the interference signal within the surrounding noise.

Accordingly, the object of the invention is to create a measurement device and method for processing a first input signal, which is part of a measurement signal. The object is solved by the features of claim 1 for the device and claim 10 for the method. The dependant claims contain further developments.

An inventive measurement device for measuring a first input signal, which is part of a measurement signal comprises a measurement unit set up for measuring the first input signal within a signal derived from the measurement signal, a transformation unit set up for transforming the measurement signal or a signal derived from the measurement signal into the frequency-domain resulting in a first frequency-domain signal, a filter unit set up for removing components of the first

frequency-domain signal which correspond to a second input signal, which is part of the measurement signal, resulting in a first filtered signal, and an inverse transformation unit set up for transforming the first filtered signal into the time-domain resulting in a first time-domain signal.

The measurement unit is preferably set up for measuring the first input signal within the first time-domain signal or a signal derived from the first time-domain signal. It is thereby possible to remove the second input signal from the measurement signal before measuring the remaining first input signal. This greatly increases the measurement accuracy . Advantageously, the power of the second input signal is higher than the power of the first input signal by a factor of higher than 1.2, preferably higher than 2, most preferably higher than 10. This results in a high gain in measurement accuracy by use of the inventive device.

Preferably, the transformation is a Fourier transformation and the inverse transformation is an inverse Fourier transformation. Alternatively, the transformation is a fast Fourier transformation and the inverse transformation is an inverse fast Fourier transformation. In a further alternative, the transformation is a Karhunen-Loeve transformation and the inverse transformation is an inverse Karhunen-Loeve transformation. These different transformations allow a user to control the required processing time and the resulting accuracy.

Preferably, the measurement device further comprises an acquisition unit set up for detecting the presence of the second input signal within the measurement signal and for acquiring the second input signal within the measurement signal resulting in a first acquired signal. The

transformation unit is then set up for transforming the first acquired signal or a signal derived from the first acquired signal into the frequency domain resulting in the first frequency-domain signal. Signals not centered around a center frequency of zero can now be processed. Optionally, the measurement signal comprises a third input signal. The transformation unit is then set up for

transforming a signal derived from the first time-domain signal into the frequency-domain resulting in a second frequency-domain signal. The filter unit is then set up for removing components of the second frequency-domain signal which correspond to the third input signal, resulting in a second filtered signal. The inverse

transformation unit is then set up for transforming the second filtered signal into the time-domain resulting in a second time-domain signal. Finally, the measurement unit is then set up for measuring the first input signal within the second time-domain signal or a signal derived from the second time-domain signal. It is now possible to remove more than one signal components corresponding to the signals of more than one GPS satellites. This further increases the measurement accuracy.

transformation unit is then set up for transforming the first acquired signal or a signal derived from the first acquired signal into the frequency domain resulting in the a first frequency-domain signal. The measurement unit is then set up for detecting the presence of the third input signal within the measurement signal, and for acquiring the third input signal within the first time-domain signal or a signal derived from the first time-domain signal resulting in a second acquired signal. The transformation unit is then set up for

transforming the second acquired signal or a signal derived from the second acquired signal into the frequency domain resulting in the second frequency-domain signal. It is now possible to process signal components, that are not centered around a center frequency of zero.

Preferably, the measurement device further comprises an inverse spreading unit set up for despreading the first acquired signal by multiplying it with a first predefined pseudo-noise sequence resulting in a first despread signal, and for respectively despreading the second acquired signal by multiplying it with a second predefined pseudo-noise sequence resulting in a second despread signal. The transformation unit is then set up for

transforming the first despread signal into the frequency domain resulting in the first frequency-domain signal, and for respectively transforming the second despread signal into the frequency domain resulting in the second

frequency-domain signal. The measurement device preferably comprises a spreading unit set up for spreading the first time-domain signal by multiplying it with the first predefined pseudo-noise sequence resulting in a first spread signal, and for respectively spreading the second time-domain signal by multiplying it with the second predefined pseudo-noise sequence resulting in a second spread signal. The measurement unit is then set up for measuring the first input signal within the first spread signal or respectively the second spread signal.

It is now possible to process more than one signal

components, which are spread spectrum signals.

An inventive processing method aims at measuring a first input signal, which is part of a measurement signal. The first input signal is measured within a signal derived from the measurement signal. The following steps are performed :

- transforming the measurement signal or a signal derived from the measurement signal into the frequency-domain resulting in a first frequency-domain signal,

- removing components of the first frequency-domain signal which correspond to a second input signal, which is part of the measurement signal, resulting in a first filtered signal, and

- transforming the first filtered signal into the time- domain resulting in a first time-domain signal.

Preferably the first input signal within the first time- domain signal or a signal derived from the time-domain signal is measured. It is thereby possible to remove the second input signal from the measurement signal before measuring the remaining first input signal. This greatly increases the measurement accuracy. An exemplary embodiment of the invention is now further explained with respect to the drawings, in which Fig. 1 shows several exemplary signals within the GPS context ;

Fig. 2 shows an exemplary embodiment of the inventive device ;

Fig. 3 depicts a first signal in the frequency domain;

Fig. 4 shows a second signal in the frequency domain, and

Fig. 5 shows an exemplary embodiment of the inventive method . First we demonstrate the underlying function of a spread spectrum transmission within the GPS system with respect to Fig. 1. In a second step, the construction and function of an exemplary embodiment of the inventive device is shown along Fig. 2. The function of an exemplary

embodiment of the inventive device and of an exemplary embodiment of the inventive method is further deliberated on regarding Fig. 3 - Fig. 4. Finally, the function of an embodiment of the inventive method is explained along Fig. 5. Similar entities and reference numbers in different figures have been partially omitted.

The present invention is explained along an example signal from the global positioning system (GPS) . The invention is not limited to GPS signals. Any other signals, which are stronger than the respective inband interference, can be used. The Global Positioning System is a satellite

navigation system and belongs to the category of Global Navigation Satellite Systems (GNSS) . The satellites orbit the earth in a height of around 20200 km with a speed of 3.87 km per second. This corresponds to a circulation time of 11 hours and 58 minutes. The satellites are arranged equispaced on six orbital planes, with each plane

containing at least four satellites. The inclination angle of the planes against the equatorial plane is 55 degrees and the rotation of the six planes towards each other is 60 degrees. GPS uses two different coded signals. One is encoded and reserved for military use only. Although the second signal has always been available for civilian use, it was intentionally degraded (Selective Availability) , making position determination very imprecise. In 2000, Selective Availability was turned off, which improved the precision of civilian GPS from around 100m to around 10m. A precise determination of a receiver' s position on earth is possible if the signal of at least four satellites is received simultaneously. The overall number of satellites in space and their constellation ensure that this is possible all over the world.

There are frequency bands which are advantageous for global navigation satellite systems. The Global

Positioning System uses two radio frequencies which are referred to as Link 1 (LI) and Link 2 (L2) . They both are derived from a reference frequency fo = 10.23MHz. The resulting frequencies are f_Ll = 154 * fo = 1575.42MHz and f_L2 = 120*f₀ = 1227.60MHz.

These frequencies are very accurate as the mentioned reference frequency is an atomic frequency standard. L2 is exclusively used to transmit the encoded signal for military use whereas the LI frequency contains both, the military and civilian signal. We only focus on the LI civilian signal in the following.

GPS makes use of the direct-sequence-spread-spectrum technique (DSSS) . The data signal is multiplied by a spreading sequence, also called as pseudo-random-noise (PRN) code or chipping sequence or pseudo-noise (PN) sequence. The spreading sequence is of a higher bit rate than the user data. The bits of this sequence are denoted as chips because one single bit does not directly hold any information .

The process of spreading and despreading will be

demonstrated in the following in Fig. 1. A continuous wave signal 3 is multiplied by a pseudo-random-noise (PRN) signal 2 resulting in a spread signal 1. The signals 1 - 3 are depicted in the time-domain in Fig. 1. In the

frequency-domain, the continuous wave signal 3 has a very narrow bandwidth. By multiplying it with the pseudo- random-noise signal 2, the bandwidth of the continuous wave signal 3 is significantly enlarged. The spread signal 1 has a far greater bandwidth than the continuous wave signal 3. At the same time, the power of the continuous wave signal 3 is distributed over this far larger

bandwidth. In a real-world environment, naturally, instead of the continuous wave signal 3, a signal comprising data would be used.

In order to retrieve the original signal 3, the spread signal 1 is again multiplied with the identical pseudo^¬ random-noise sequence. In a real-world environment, several GPS signals of different satellites are received at the same time by a receiver. Each satellite uses a different pseudo-random-noise sequence. The individual signals of the different satellites can be retrieved by multiplying the total signal with the individual pseudo^¬ random-noise sequences. The presently retrieved original signal is easily distinguishable from the resulting signal. The signals of the remaining satellites are not despread, since the wrong pseudo-random-noise sequence has been used. Therefore, these signals are not despread and remain within the signal as noise.

The sum of all of these different GPS satellite signals creates a relatively high noise level. It is difficult to detect an interference signal within this high noise level. The underlying idea of the present invention therefore is to remove the individual satellite signals from the total signal in order to lower the overall noise level. After removing all the individual satellite

signals, the interference signal can more easily be detected .

In Fig. 2, an exemplary embodiment of the inventive measurement device is shown. A control unit 20 is

connected to a high frequency unit 21, an acquisition unit 22, a despreading unit 23, a transformation unit 24, a filter unit 25, an inverse transformation unit 26, a spreading unit 27 and a measurement unit 28. The high frequency unit 21 is connected to a signal input and to the acquisition unit 22. The acquisition unit 22 is connected to the despreading unit 23, which again is connected to the transformation unit 24. The

transformation unit 24 is connected to the filter unit 25, which in turn is connected to the inverse transformation unit 26. The inverse transformation unit 26 is connected to the spreading unit 27, which is connected to the acquisition unit 22 and to the measurement unit 28. The control unit 20 controls the functions of all other units 21 - 28.

A high frequency input signal 30 is supplied to the high frequency unit 21 through the signal input. The high frequency input signal comprises at least the interference signal, which is referred to as first input signal in the following. Furthermore the high frequency input signal 30 comprises at least a second input signal, which

corresponds to the high power signal, e.g. a single GPS signal . The high frequency unit 21 downconverts the frequency of the high frequency input signal 30 and digitizes the signal. The resulting measurement signal 31 is transmitted to the acquisition unit 22. The acquisition unit 22 detects the signals of the individual satellites. In a first pass, the acquisition unit 22 focuses on the second input signal which corresponds to the spread spectrum signal of a first satellite.

The acquisition unit 22 centers the frequency of the measurement signal around the central frequency of the second input signal. Doppler-shift is thereby removed. The resulting first acquired signal 32i is transmitted to the despreading unit 23. The despreading unit 23 multiplies the signal with a pseudo-random-noise sequence. This results in a despreading of the first acquired signal 32 . The resulting first despread signal 33i is transmitted to the transformation unit 24, which transforms the signal into the frequency-domain. For this transformation, a Fourier transform or a fast Fourier transform or a

Karhunen-Loeve transform or any other transformation, which transforms a signal from the time-domain into the frequency-domain, can be used.

The resulting first frequency-domain signal 34i now comprises a narrow band despread GPS signal, which

corresponds to the second input signal at the central frequency .

The first frequency-domain signal 34i is then transmitted to the filter unit 25. The filter unit 25 is configured to remove the portion around the central frequency. Therefore the signal portion corresponding to the second input signal is removed from the first frequency-domain signal 34i. This results in a first filtered signal 35i. This first filtered signal 35i therefore does no longer

comprise signal components corresponding to the second input signal. The remaining signal 35i therefore only comprises the first input signal, which is the

interference signal and possibly further input signals, which correspond to the signals of other GPS satellites. The first filtered signal 35i is then transmitted to the inverse transformation unit 26, which performs a

transformation into the time-domain. The inverse

transformation unit 26 uses the inverse of the

transformation that has been used by the transformation unit 24. The resulting time-domain signal 36i is afterwards

transmitted to the spreading unit 27, which again

multiplies the time-domain signal 36i with the pseudo- random-noise sequence, with which already the despreading unit 23 multiplied the first acquired signal 32i.

This results in a spreading of the first time-domain signal 36i. The resulting first spread signal 31 i now corresponds to the original first acquired signal 32i but does not longer comprise components relating to the second input signal . In case, no further input signals apart from the first input signal, which corresponds to the interference to be measured, are present, it is transmitted to the

measurement unit 28 and measured. In case, the first spread signal 31 i though comprises further input signals, it is again transmitted to the acquisition unit 22, which acquires a third input signal, which corresponds to the GPS satellite signal of a second satellite. The same processes are repeated for this third input signal as shown before. This sequence is repeated, until now further input signal apart from the first input signal is present within the resulting spread signal 31 .

The signals of this first iteration are labeled with an index 1. For further reference, signals of further

iterations are labeled with the respective number of the iteration as an index reference number.

As already explained, the present invention is not limited to the GPS system. In case, the signals to be removed from the measurement signal 31 are not spread spectrum signals, the inventive device does not comprise a despreading unit 23 and a spreading unit 27. The acquisition unit 22 is then directly connected to the transformation unit 24 and the inverse transformation unit 26 is directly connected to the acquisition unit 22 and to the measurement unit 28. Also, the acquisition unit 22 is not absolutely necessary. In case the exact frequency positions of the individual input signals are known, the acquisition unit 22 can be omitted. In this case, the high frequency unit 21 is directly connected to the despreading unit 23 or

respectively the transformation unit 24. Then, the

spreading unit 27 or respectively the inverse

transformation unit 26 is directly connected to the despreading unit 23 or respectively the transformation unit 24.

We will not go into detail about the function of the measurement unit 28, since the function of this unit corresponds to the function of a regular high frequency measurement device.

In Fig. 3 an exemplary GPS signal 10 after despreading is shown. It is easily recognizable that the signal is centered around a frequency of zero and comprises a strong signal peak 11 at the central frequency. This strong peak 11 corresponds to the input signal of the individual satellite to with the employed pseudo-random-noise

sequence corresponds to. The signal 10 shown in Fig. 3 corresponds to the frequency-domain signal 34 of Fig. 2. The filter unit 25 of Fig. 2 is set up for removing exactly this central peak 11 while removing as little as possible of the remaining signal 10. Fig. 4 shows a second exemplary signal 12. The signal 12 is also depicted in the frequency-domain centered around a frequency of f = 0. The signal 12 shown here does no longer comprise a central peak, since all input signals resulting from GPS satellite signals have been removed from this signal 12. The only peak 13 still present within the signal 12 therefore corresponds to the first input signal, which is identical to the interference signal to be measured. The signal 12 corresponds to the spread signal 37, which is transmitted to the measurement unit 28 for measurement. In contrast to the spread signal 37, the signal 12 though is in the frequency-domain.

Fig. 5 finally shows a flow chart of an exemplary

embodiment of the inventive method. A measurement signal comprises a first input signal, which corresponds to the interference signal to be measured and a second input signal of higher power, which prevents the first input signal from being measured. This second input signal is to be removed.

In a first step 40, the second input signal is acquired. The frequency of the measurement signal is centered around the center frequency of the second input signal. In a second step 41, a despreading of the entire measurement signal is performed. This is done by multiplying the signal with a pseudo-random-noise sequence. In a third step 42, the resulting signal is transformed into the frequency-domain. For this transformation, a Fourier transformation, a fast Fourier transformation or a

Karhunen-Loeve transformation is employed. The resulting signal therefore is now in the frequency-domain. It is filtered in a fourth step 43. The filtering removes a portion around the center frequency of this signal. This center portion corresponds to the second input signal, which has been narrowed to a narrow band signal by the second step of despreading the measurement signal.

In a fifth step 44, an inverse transformation is performed on the filtered signal. The employed inverse

transformation is the inverse of the transformation performed in the third step 42. The resulting signal is again spread in a sixth step 45. This is done by

multiplying the signal with the same pseudo-random-noise sequence as has already been used in the despreading step 41. In case no further input signals apart from the interference signal are present within the resulting signal, this resulting signal is finally measured in a seventh step 46. In case, further input signals are present though within the spread signal, the steps 40 - 45 are repeated using this signal as an input signal. The steps of acquisition 40, despreading 41 and spreading 45 have to be considered as optional steps. The steps of despreading 41 and spreading 45 though can only be omitted both at the same time. An omission of these steps 40, 41 and 45 is also only possible, if the input signal allows this, since is not a spread spectrum signal. The measuring step 46 is also optional in case any signal processing and no measurement is performed.

The invention is not limited to the examples and

especially not to the GPS system. The characteristics of the exemplary embodiments can be used in any beneficiary combination of any features disclosed in the

specification, claims and/or drawings.

Claims

1. Measurement device for measuring a first input signal, which is part of a measurement signal (31), comprising: -a measurement unit (28) for measuring the first input signal within a signal (37^ ₂) derived from the

measurement signal (31),

- a transformation unit (24) for transforming the

measurement signal (31) or a signal (33i, ₂) derived from the measurement signal (31) into the frequency-domain resulting in a first frequency-domain signal (34i) ,

- a filter unit (25) for removing components of the first frequency-domain signal (34i) which correspond to a second input signal, which is part of the measurement signal (31), resulting in a first filtered signal (35i) , and

- an inverse transformation unit (26) for transforming the first filtered signal (35i) into the time-domain resulting in a first time-domain signal (36i) ,

2. Measurement device according to claim 1

characterized in that

the measurement unit (28) is set up for measuring the first input signal within the first time-domain signal (37i) or a signal (37₂) derived from the time-domain signal (37i) .

3. Measurement device according to claim 1 or 2,

characterized in

that the power of the second input signal is higher than the power of the first input signal by a factor of higher than 1.2, preferably higher than 2, most preferably higher than 10.

4. Measurement device according to any of claims 1 to 3, characterized in

that the transformation is a Fourier transformation and the inverse transformation is an inverse Fourier

transformation, or

that the transformation is a fast Fourier transformation and the inverse transformation is an inverse fast Fourier transformation, or

that the transformation is a Karhunen-Loeve transformation and the inverse transformation is an inverse Karhunen- Loeve transformation.

5. Measurement device according any of the claims 1 to 4, characterized in

that the measurement device further comprises an

acquisition unit (22) up for detecting the presence of the second input signal within the measurement signal (31) and for acquiring the second input signal within the

measurement signal (31) resulting in a first acquired signal (32i) , and

that the transformation unit (24) is set up for

transforming the first acquired signal (32i) or a signal (33i) derived from the first acquired signal (32i) into the frequency domain resulting in the first frequency- domain signal (34i) .

6. Measurement device according any of the claims 1 to 5, characterized in

that the measurement signal (31) comprises a third input signal,

that the transformation unit (24) is set up for

transforming a signal (32₂) derived from the first time domain signal (37i) into the frequency-domain resulting in a second frequency-domain signal (34₂) ,

that the filter unit (25) is set up for removing

components of the second frequency-domain signal (34₂) which correspond to the third input signal, resulting in a second filtered signal (35₂) ,

that the inverse transformation unit (26) is set up for transforming the second filtered signal (35₂) into the time-domain resulting in a second time-domain signal

(36₂), and

that the measurement unit (28) is set up for measuring the first input signal within the second time-domain signal (36₂) or a signal (37₂) derived from the second time- domain (36₂) signal.

7. Measurement device according claim 6,

characterized in

that the measurement device further comprises an

acquisition unit (22) set up for detecting the presence of the second input signal within the measurement signal (31) and for acquiring the second input signal within the measurement signal (31) resulting in a first acquired signal (32i) , and/or

that the transformation unit (24) is set up for

transforming the first acquired signal (32i) or a signal (33i) derived from the first acquired signal (32i) into the frequency domain resulting in the a first frequency- domain signal (34i) , and/or

that the measurement unit (28) is set up for detecting the presence of the third input signal within the measurement signal (31), and for acquiring the third input signal within the first time-domain signal (36i) or a signal (37i) derived from the first time-domain signal (36i) resulting in a second acquired signal (32₂), and/or that the transformation unit (24) is set up for

transforming the second acquired signal (32₂) or a signal (33₂) derived from the second acquired signal (32₂) into the frequency domain resulting in the second frequency- domain signal (34₂) .

8. Measurement device according any of the claims 1 to 7, characterized in

that the measurement device further comprises an inverse spreading unit (23) set up for

- despreading the first acquired signal (32i) by

multiplying it with a first predefined pseudo-noise sequence resulting in a first despread signal (33i) , and

- respectively despreading the second acquired signal (32₂) by multiplying it with a second predefined pseudo- noise sequence resulting in a second despread signal (33₂) , and/or

that the transformation unit (24) is set up for

- transforming the first despread signal (33i) into the frequency domain resulting in the first frequency-domain signal (34i) , and

- respectively transforming the second despread signal (33₂) into the frequency domain resulting in the second frequency-domain signal (34₂) .

9. Measurement device according to claim 8,

characterized in

that the measurement device comprises a spreading unit (27) set up for - spreading the first time-domain signal (36i) by

multiplying it with the first predefined pseudo-noise sequence resulting in a first spread signal (37i) , and

- respectively spreading the second time-domain (362) signal by multiplying it with the second predefined pseudo-noise sequence resulting in a second spread signal (312 ) , and/or

that the measurement unit (28) is set up for measuring the first input signal within the first spread signal (37i) or respectively the second spread signal (37₂) .

10. Measurement method for processing a first input signal, which is part of a measurement signal (31), wherein the first input signal is measured within a signal (37i_f 2) derived from the measurement signal (31),

comprising the steps:

- transforming the measurement signal or a signal (33i, 2) derived from the measurement signal (31) into the

frequency-domain resulting in a first frequency-domain signal (34_x) ,

- removing components of the first frequency-domain signal (34i) which correspond to a second input signal, which is part of the measurement signal (31), resulting in a first filtered signal (35i) , and

- transforming the first filtered signal (35i) into the time-domain resulting in a first time-domain signal (36i) .

11. Measurement method according to claim 10,

characterized by

measuring the first input signal within the first time- domain signal (37i) or a signal (37₂) derived from the time-domain signal (37i) .

12. Measurement method according to claim 10 or 11,

characterized in

that the power of the second input signal is higher than the power of the first input signal by a factor higher than 1.2, preferably higher than 2, most preferably higher than 10.

13. Measurement method according to any of the claims 10 to 12,

characterized in

transformation, or

14. Measurement method according any of the claims 10 to 13,

characterized by

- detecting the presence of the second input signal within the measurement signal (31) and acquiring the second input signal within the measurement signal (31) resulting in a first acquired signal (32i) , and by

- transforming the first acquired signal (32i) or a signal (33i) derived from the first acquired signal (32i) into the frequency domain resulting in the first frequency- domain signal (34i) .

15. Measurement method according any of the claims 10 to 14,

characterized by

- the measurement signal (31) comprising a third input signal,

- transforming a signal (32₂) derived from the first time domain signal (37i) into the frequency-domain resulting in a second frequency-domain signal (34₂) ,

- removing components of the second frequency-domain signal (34₂) which correspond to the third input signal, resulting in a second filtered signal (35₂) ,

- transforming the second filtered signal (35₂) into the time-domain resulting in a second time-domain signal

(36₂) , and

- measuring the first input signal within the second time- domain signal (36₂) or a signal (37₂) derived from the second time-domain (36₂) signal.

16. Measurement method according claim 15,

characterized by

- detecting the presence of the second input signal within the measurement signal (31) and acquiring the second input signal within the measurement signal (31) resulting in a first acquired signal (32i) ,

- transforming the first acquired signal (32i) or a signal (33i) derived from the first acquired signal (32i) into the frequency domain resulting in the a first frequency- domain signal (34i) ,

- detecting the presence of the third input signal within the measurement signal (31) and acquiring the third input signal within the first time-domain signal (36i) or a signal (37i) derived from the first time-domain signal

(36i) resulting in a second acquired signal (32₂) , and - transforming the second acquired signal (32₂) or a signal (33₂) derived from the second acquired signal (32₂) into the frequency domain resulting in the second

frequency-domain signal (34₂) .

17. Measurement method according any of the claims 10 to 16,

characterized by

- despreading the first acquired signal (32i) by

multiplying it with a first predefined pseudo-noise sequence resulting in a first despread signal (33i) ,

- respectively despreading the second acquired signal (32₂) by multiplying it with a second predefined pseudo- noise sequence resulting in a second despread signal (33₂),

and/or

18. Measurement method according to claim 17,

characterized by

- spreading the first time-domain signal (36i) by

multiplying it with the first predefined pseudo-noise sequence resulting in a first spread signal (37i) ,

- respectively spreading the second time-domain (36₂) signal by multiplying it with the second predefined pseudo-noise sequence resulting in a second spread signal (37₂) , and - measuring the first input signal within the first spread signal (37i) or respectively the second spread signal (37₂) .