WO2010066729A1

WO2010066729A1 - Method and device for correlating signals

Info

Publication number: WO2010066729A1
Application number: PCT/EP2009/066625
Authority: WO
Inventors: Jón Winkel
Original assignee: Ifen Gmbh
Priority date: 2008-12-10
Filing date: 2009-12-08
Publication date: 2010-06-17
Also published as: DE102008061417A1

Abstract

The invention relates to a method for correlating signals in a receiver. In said method a frequency change of the received signal, said change caused by the movement of the receiver, is compensated during the temporal integration interval.

Description

METHOD AND DEVICE FOR CORRELATING SIGNALS

The invention relates to a method for correlating signals, a correlator unit, a signal processing unit and a receiver.

Embodiments of the invention are illustrated in the figures and are explained in more detail below.

Show it

FIG. 1 shows a sensor-based receiver according to the prior art,

FIG. FIG. 2A shows the code phase Doppler shift relationship in FIG

Ideally,

FIG. 2B shows the code phase Doppler shift relationship in the unmatched case, FIG. 3A and 3B are methods for correlating signals according to embodiments of the invention,

FIG. 4 a method for correlating signals according to an embodiment of the invention,

FIG. 5 shows another method for correlating signals according to an embodiment of the invention, and

FIG. 6 an embodiment of the invention.

The two areas that are relevant to the present invention are on the one hand GNSS receivers with high sensitivity (in English "High Sensitivity GNSS") and support of a GNSS receiver by local sensors (such as inertial navigation systems INS (Inertial Navigation System)). The technique used in high-sensitivity GNSS receivers focuses on acquisition and tracking in poor signal-to-noise ratios based on the duration of the coherent correlation between the received signal and the reference signal {Hereinafter referred to as "coherent integration").

Under correlation in this description is the

Comparing a signal, such as a code or part of a signal with another signal understood.

Integration in connection with the correlation is understood in this description to be the mathematical integration that is carried out using the means of signal processing known to the person skilled in the art, in particular digital signal processing. This means in particular that the integration is effected by an addition or summation.

Under baseband signal is understood in this description, a signal that has no carrier frequency components or has only residual parts that remain from the mixture of two not exactly the same frequencies.

Such a comparison may be digital, for example by multiplication and addition of sampled values of the

Signal can be achieved with a stored signal within a predefined time interval. In the case of coherent integration, the result obtained in this predefined time interval becomes directly for the following Processing stages used. That is, it is not cached and associated with a subsequent correlation of the next time interval by eg addition.

The correlation can be made both in the time domain by methods using e.g. so-called matched filter or matched filter or a large number of correlators as well as in the frequency domain, for example by FFT (Fast Fourier

Transformation) methods are implemented. These methods make it possible to acquire the signal under bad signal conditions in a short time. Typically, it is impossible to receive the data modulated on the signal.

This is remedied by the so-called Assisted GNSS (Global Navigation Satellite System).) In this case, a GNSS receiver receives information for calculating the satellite orbits via a data connection (eg via GSM (Global System for Mobile Communications), UMTS (Universal Mobile Telecommunications System), WLAN (Wireless Local Area Network), etc.) It is also possible that coarse position data (with an accuracy of, for example, 1 km) and time are transmitted as well, which allows the receiver to restrict the search space during signal acquisition.

In order to achieve the highest possible sensitivity, the duration of the coherent integration, ie the time interval over which is integrated, must be selected as high as possible. As a rule, the coherent integration time is limited by the data rate, as a Data bit change interrupts the coherence. There are approaches to solve this problem. Since, with the knowledge of the data bits, the data modulation can reversibly be reversed and a data bit-free signal is obtained, eg the data bits are transmitted in real time to the receiver. The data bits can thus be applied to increase the duration of the coherent integration.

The second method relevant to this invention is to support GNSS signal tracking by external sensors that measure the motion dynamics of the receiver. Nowadays common methods realize this either at the position level, at the level of the so-called raw data or even at the loop level: The dynamics are measured by external sensors and used to control the frequencies of the Numerically Controlled Oscillators (NCOs).

The method of loop support is outlined in FIG.

The received signal (102) is converted to baseband with the frequency compensation (106).

The signal is multiplied by the sine or cosine of the frequency of the frequency change determined by the PLL / FLL filter.

Subsequently, the result from the

Frequency compensation (106) multiplied by the locally generated reference signal and coherently integrated (108). The reference signal (128) is typically generated in 3 executions: early, punctual and late. The Result of integration (108) with the punctual signal

(Ip> Qp) is forwarded to the PLL / FLL signal tracking system (110,112,114,104,106,108). The remaining

Signals (Λr> S _e >Λ> ß /) are forwarded to the DLL signal tracking system

(118,120,122,126,128,108). For both systems so-called discriminators PLL / FW ^ DU (110,118) are formed, which estimate the phase deviation of the carrier phase (PLL) / carrier frequency (FLL) or the code phase (DLL). The result is filtered (F _{PLL / FLL} (s) (112) and F _DLL (s) (120)) and scaled (L _PLL (114) and L _DLL (122)). The output from the external sensors (eg INS) (130) is additionally used to determine the valid frequency offset for the next integration interval. It is important that the frequency offset during the integration remains constant.

The sensitivity of a receiver is essentially determined by the duration of the coherent integration. The maximum settable coherent integration time is in turn limited upwards uA by the dynamic movement of the receiver. In FIG. 2A and 2B, the problem is outlined. FIG. Fig. 2A shows the search space (s) for the acquisition. The vertical axis (202) indicates the scheduled frequency shift and the horizontal axis (204) indicates the code phase. Typically, an integral over the code phase is calculated for a given frequency shift. This can be realized either in the time domain (eg by massive parallel processing) or in the frequency domain. The required accuracy of the frequency shift during integration is inversely proportional to the coherent integration time. This means that the longer the integration time, the more accurate the frequency shift must be known. If integration times in the range of 1 second are to be achieved, the movement of the receiver plays an increasing role. The situation is shown in FIG. 2B. The search space or the coherent integration path must be adapted dynamically during the integration. Ie The common assumption about the constancy of the frequency shift, or the code Doppler is no longer valid. Would this assumption in the

Situation as shown in FIG. 2B, the result would be greatly reduced. This problem applies to both the acquisition and the signal tracking.

The traditional approaches to supporting signal processing by external sensors (such as INS) only support signal tracking of tracking loops and do not intervene in the correlation process itself. That the problem described above is not resolved by the prior art.

The object of the invention is to compensate the acceleration and higher-order dynamic terms on the line-of-sight during coherent integration. This applies both during acquisition and during signal tracking.

The object is achieved by a method according to claim 1. The object is further achieved by a correlator unit according to claim 15, by a signal processing unit according to claim 19 and by a receiver according to claim 25. The receiver receives from a sensor acceleration and higher order dynamic terms (BDTHO) projected onto the line of sight of a transmitter. This sensor measures accelerations and rotation rates or makes them available in other ways. These data are either related to a ground-based and earth-centered coordinate system or to a local coordinate system of the sensor. The receiver transforms the BDTHO by means of the position, if necessary, into the earth-fixed and earth-centered coordinate system in which the receiver operates. The result is projected onto the connecting line between satellite and receiver. This information consists, for example, of frequency information already determined by the receiver, such as storage of transmitter movements, clock behavior, estimates from a control loop or from stored information.

In Figure 4, the method is further illustrated. A first signal (302), for example, which has transmitted a satellite and which is received by a receiver in which the method is applied, is multiplied by a second signal (304) in (306). The first signal may e.g. a signal with a high frequency, carrier frequency or a down-mixed in antecedents of the receiver to an intermediate frequency signal. Typically, the first signal (302) is a sampled digital signal. The second signal (304) is, for example, a signal generated by the receiver itself, which the receiver has generated by means of further information.

If the receiver does not yet have accurate information about the first signal (302) or not yet has recognized, he must "acquire" the signal, ie the receiver is made of eg a memory data, such as frequency information and

Synchronization information, fetch and try to use this information to recognize the signal. The

Signal recognition takes place in CDMA (Code Division Mulitple Access), for example via a correlation. In such a correlation, in principle, two signals are compared for similarity, or better, equality. The correlation will be successful if the frequencies, the CDMA sequence and the CDMA bit rate (often called chip rate) are nearly identical. Unsuccessful acquisition as well as signal loss in signal tracing can be e.g. occur when the line of sight from the transmitter to the receiver is e.g. acceleration, high dynamics, resulting in high Doppler values or when the time interval beyond that is integrated in the correlation due to high demands on the sensitivity of the receiver must be set high. Since these two parameters do not affect each other, it is possible, by adjusting the signal dynamics (Doppler) during a correlation interval, to follow the consequences of the long integration time, i. that the synchronism between the chips of the baseband signal and the third signal is lost, as by beating the integration negates the negative and positive beat half-wave over the integration time, and for a correlation to have an unsuccessful result.

In one embodiment of the invention, therefore, as shown in FIG. 3A, a method for correlating signals is provided in which a first signal (302) has a first frequency, a second signal (304) has a second frequency, a third signal (310) is a predefined signal, and wherein the first signal

(302) is multiplied (306) with a second signal (304), the multiplied signal (306) with the third

Signal (310) is correlated during a time interval or, as shown in FIG. 3B shown, the third

Signal (310) is multiplied by the second signal (304) and the multiplied signal (350) is correlated with the first signal during a time interval (308). According to this embodiment, the second frequency is changed during the time interval. According to an embodiment of the invention, the correlation is applied to the acquisition of the first signal (302).

Hereby it is achieved that by multiplying a by e.g. a sudden movement of the receiver changed first, received signal (302) with a second signal generated by the receiver (304) ideally no or at most a slight beating signal arises because in the second signal (304) the change due to the dynamics is taken into account, during the integration interval.

If the time interval over which is integrated is large compared with the storage of the chip rate, the synchronism between the chips of the baseband signal and the third signal (code) (310) is also lost. Again, it is important that a change in the chip rate offset caused, for example, by movement of the receiver, be considered during an integration interval. The signal (302, 310) may be a binary code. It can also be a complex code. The coherent integration (correlation) can also be approximated by smaller integration intervals where the frequency remains constant. The smaller intervals are then added coherently taking into account an additional phase shift. Frequency corrections (Doppler on the carrier phase and the code) are reapplied for each interval.

In one embodiment of the invention, therefore, the predefined third signal (310), which consists of a code having a code rate, is changed during the temporal interval. In order to first reconcile the frequency, a possible frequency is first tried out in the acquisition case by multiplying the second signal (304) by the first frequency (306, 350) to obtain a baseband signal, which is then combined with the third signal (310 ), ie the code is correlated (306,350). If this does not succeed, another frequency for the second signal (304) is tried out according to a specific scheme or algorithm.

But it is also as above with reference to FIG. 3B, according to one embodiment, it is possible to rearrange the order of operations so that first the code signal (310) is multiplied (350) with the generated second signal (304) and the resulting signal is correlated with the received first signal (302) (FIG. 308).

Since the code may be shifted to baseband, ie not synchronized, it will also be determined here Algorithms or presets of the code generated by the receiver shifted to achieve synchronization. The pure code shift (synchronization of the code with the baseband signal at the start time of integration), however, is secondary to the invention.

In another embodiment, the correlation is used to track the first signal. Namely, if the receiver has already recognized the signal, its task is to continue to follow the signal. He can accomplish this by constantly using correlation, i. For example, integration over a predetermined time interval that "measures" current frequency and tracks deviations from its self-generated signal (e.g., the "second" signal). Correlation for signal tracking has similar problems to signal acquisition. If integrated over a long period of time, the negative half-wave of the beat comes from the multiplication of the received first signal with the self-generated second signal (304) and the synchronicity of the codes of the baseband signal (306) and the self-generated code (310). This can result in the receiver, if it is experiencing a movement, e.g. an acceleration, rotation or shock, experiences the signal loses.

According to the invention, the same measures can be taken in the signal tracking as in the Signalakqusition, as already described above.

According to one embodiment of the invention, in the case of signal tracking, the changes in the second frequency and / or the code rate become information a control loop feedback and independent of the control loop information determined. 5, which shows the case of the signal trace, it is clear that information from the unit 336, which is part of the control loop 304, 306, 308, 330 and 336, and information independent from the control loop from the branch 322, 324, 328 in 312 and the merged information in 304 results in a change of the second frequency.

In the case of signal acquisition, according to an embodiment of the invention, the change in the second frequency and / or the code rate is determined from a value predefined for a correlation interval and from information that is independent of this predefined value.

This is illustrated in Fig. 4, which shows the case of signal acquisition, in which instead of a control loop an independent information source 402 can be seen, e.g. Has access to stored frequency values, or the frequency values e.g. is generated according to a predetermined scheme or by means of an algorithm, or to the frequency values e.g. can be sent by command.

According to another embodiment, one or more sensors (322) provide data for the change of the second frequency. This one or more sensors (322) are motion sensors according to another embodiment. Motion sensors are understood to mean sensors, the uniform or accelerated movements, higher-order movements, the direction of movement etc., ie they can measure and transmit this information via an analogue or digital interface. Such sensors are for example able to detect case, tilt angle, movement, position, vibration and vibration.

Other sensors that may be considered: compass,

Pressure sensor {altitude measurement}, systems designed by

Motion sensors are derived or based on it, such. Pedometer.

According to a further embodiment, the independent information is obtained from preprocessing the raw sensor data. That is, the data provided by the sensor (322) or the sensors are so-called raw data which provide motion data, but which is e.g. still have no relation to the line of sight receiver satellite. Thus, for example, these data must first be set in relation to a defined global coordinate system, e.g. an ECEF (Earth Centered Earth Fixed) coordinate system, or by means of the geometry of the transmitting station, e.g. Satellite, and the receiver can be converted, scaled and / or rotated in such a way that a Doppler shift, Doppler acceleration or other values can be calculated, which can have an influence on the received frequency.

According to one embodiment, a stored motion scenario provides data for the change of the second frequency. This can be done eg within a simulation or be a planned movement scenario. It would also be conceivable, the motion information directly from motion control, for example, a moving Object to which the receiver is attached to receive. In this way, instead of measuring the movement, the information could be obtained directly from the control of the movement, such as a drive control, motor control, etc. A corresponding algorithm could also take into account the mass and other properties of the object to be moved.

According to one embodiment, the correlation is performed by hardware correlators. That is, the correlation is expressed in e.g. Correlators that are hardwired, such as electronic components specifically designed for such operators, or components created therefor, such as ASICs.

According to one exemplary embodiment, the correlation takes place via a Fourier transformation. That is, the correlation can be performed via mathematical transformations that are mathematically equivalent to a correlation, e.g. a Fourier transform of the signals, followed by convolution and inverse transformation.

For a Fourier transformation to be performed, the function of the frequency change of the second signal over the integration interval must be known. However, since this function is known at the earliest at the end of an integration limit, the first signal must be buffered and can be applied at the earliest to the next integration interval. The function of the frequency change, once known, may then be applied directly to the received first signal (302) and to the code (310).

According to one embodiment, the frequency change from the data of the one sensor (322) or the plurality of sensors is determined by projecting the acceleration and higher order dynamic terms onto the line of sight and converting them into first and higher order Doppler values after projection.

In one embodiment, the first signal (302) is a sampled signal. That the processing of the signals takes place digitally.

According to one embodiment, a

Correlator unit having means for performing correlation during an integration interval, wherein a first signal (302) has a first frequency, a second signal (304) has a second frequency, and a third signal (310) is a predefined signal, and wherein the correlation is performed between the third signal (310) and a signal (306) resulting from a multiplication of the first signal with the second signal, or the first signal (302) and one resulting from a multiplication of the third signal (310) second signal (304) resulting signal (350).

According to this embodiment, the second signal (304) is changed during the integration interval, and the correlator unit uses the multiplication-resultant signal (306, 350) for the integration.

Since the baseband signal is obtained from a multiplication of two signals which do not have exactly the same frequency, this baseband signal remains still the difference frequency. Such a difference frequency is also often referred to as beating. The acquisition search is performed for different frequency steps resulting from the integration time.

According to one embodiment, the predefined third signal (310) consists of a code having a code rate which is changed during the temporal integration interval. The

Correlator unit uses the third integration signal (310) changing during the integration interval.

According to one embodiment, the correlator unit has hardware correlators.

According to one embodiment, the correlator unit has means for performing the correlation via a Fourier transformation or via an optimal filter. As described above, it is advantageous for the Fourier transformation if the frequency change function is known over the integration interval and the correlation unit receives this function for processing.

The above statements also apply to the following embodiments and are therefore not repeated here.

According to one embodiment, a signal processing unit is provided for processing signals, wherein a first signal (302) has a first frequency, a second signal (304) has a second frequency, a third signal (310) is a predefined signal. According to this embodiment, the signal processing unit has a frequency multiplying unit (306 or 350) for multiplying the first (302) and third signals, respectively

(310) with the second signal (304), a correlator for correlating the multiplication-resultant signal with the third (310) and first signals (302), respectively, and a frequency changing unit for changing the second frequency. The frequency changing unit has means for changing the second frequency during a time interval, and the frequency multiplying unit has means for multiplying the first and third frequencies by the second frequency changed during the time interval and relaying them to the correlator.

According to an embodiment, the third signal is a code having a code rate, and the signal processing unit additionally has one

Frequency change unit for changing the code rate of the third signal (310).

According to one embodiment, the frequency changing unit for changing the second

Frequency and the frequency change unit for changing the code rate one each

Frequency change determination unit that determines the magnitude and direction of the change in frequency by values of acceleration and higher-order dynamic terms.

According to one embodiment, the signal processing unit has a sensor data interface on, the movement data to the

Frequency change determination unit sends. The movement data may contain motion information of a higher order.

According to one embodiment, the

Signal processing unit used to acquire the first signal {302).

According to another embodiment, the

Signal processing unit used to track the first signal (302).

According to one embodiment of the invention, a receiver is provided which has a

Signal processing unit for acquisition and / or a signal processing unit for tracking the first signal (302).

Such a receiver is e.g. a navigation receiver, e.g. a GPS (Global Positioning System) or a GNSS (Global Navigation Satellite System) receiver. However, it may also be a receiver for other navigation systems or, in general, a receiver that can receive CDMA (Code Division Multiple Access) signals.

According to an embodiment, the receiver has a motion data receiver which sends motion data to the sensor data interface. The

Sensor data interface may be an internal interface of the receiver, wherein the sensor is then located within the receiver or an external interface, so that the receiver receives data from a external sensor can receive. Such an external interface may be wired or wireless.

In the following, an embodiment will be described with reference to FIG. 6 described in which a signal to the system with a

Sampling rate of 66.188 MHz and an intermediate frequency (IF) of 14.934 MHz is provided. The received signal is converted to baseband with the frequency compensation. The signal is multiplied by the sine or cosine of the sum of the nominal frequency (ie the IF) and the frequency corrections A / _P ι _L , ..., ΔJ _PL ' _L (304). It should be noted that in this example, to obtain exactly one correlation value, the frequency correction is updated M = 100 times and changed several times during an integration interval of 1 second. For example, every 10 ms the frequency with the

Value 4 / m,

⁺ 4 / _β , kt updated. Subsequently, the result from the frequency compensation is multiplied (308) and coherently integrated with the locally generated reference signal. The reference signal is generated in 3 versions: early, punctual and late. The result of

Correlation with the punctual signal

is forwarded to the PLL / FLL signal tracking system 330, 332, 334, 336, 304, 306, 308. The remaining

Signals {I _e >Qe>Ii> Qι) are forwarded to the DLL signal tracking system (338), (340), (342), (344), (348), (310), (308). For both systems so-called discriminators D _{PU! FU} , D _DLL (330), (338) are formed, which are the phase storage of the carrier phase

(PLL) / carrier frequency (FLL) or the code phase (DLL) estimate. The result is filtered (Fp _{LL / Fhh} (s) (232) and F _DhL (s) (340)) and scaled (L _PLIj (334) and L _DiL (342)). The PLL Discriminator (330) is a traditional noncoherent Costas discriminator. The loop filter (232) is a simple first-order filter with a bandwidth of, for example, 0.1 Hz. The DLL discriminator (338) is an ordinary early-end late-amplitude discriminator with a bandwidth of, for example, 0.01 Hz.

The external sensor (322) in this example is an INS that provides acceleration values in 3 orthogonal directions. In addition, the position and the rotation rates are output around all 3 axes. These data refer to the local reference system of the INS sensor. The preprocessing (324) projects the acceleration values onto the respective connecting lines between satellite and receiver. The results are scaled to the frequency and weight (K _PLL ) (326) and provided with 100 Hz to the integration process.

Claims

claims

A method for correlating signals, wherein a first signal has a first frequency, - a second signal has a second frequency, a third signal is a predefined signal

o the first signal is multiplied by a second signal, o the multiplied signal is correlated with the third signal during a time interval, or o the third signal is multiplied by the second signal, o the multiplied signal correlates to the first signal during a time interval becomes,

characterized in that

the second frequency is changed during the time interval.

2. The method according to claim 1, characterized in that

the predefined third signal consists of a code, the code has a code rate, and the code rate is changed during the time interval.

3. The method according to claim 1, characterized in that the correlation is applied to the acquisition of the first signal.

4. The method according to claim 1, characterized in that the correlation is applied for tracking the first signal.

5. The method according to claim 4, characterized in that the change of the second frequency and / or the code rate from information from a

Rule loop feedback and independent of the control loop information is determined.

6. The method according to claim 3, wherein the change of the second frequency and / or the code rate is determined from a value predefined for a correlation interval and from information independent of this predefined value.

A method according to claim 5 or 6, characterized in that one or more sensors provide the independent information.

8. The method according to claim 7, characterized in that the independent information is obtained from a preprocessing of the raw sensor data.

9. The method according to claim 7, characterized in that the one or more sensors

Motion sensors are.

10. The method according to claim 2, characterized in that a stored motion scenario data for the Changing the second frequency and / or the code rate supplies.

11. The method according to claim 1, characterized in that the correlation of hardware correlators is performed.

12. The method according to claim 1, characterized in that the correlation takes place via a Fourier transformation or via an optimum filter.

13. The method of claim 7, wherein the frequency change and / or code rate change from the data of the one or more sensors is determined by projecting the acceleration and higher order dynamic terms onto the line of sight and after projection into first and second Doppler values higher order.

14. The method according to claim 1, characterized in that the first signal is a scanned signal.

A correlator unit having means for performing correlation during an integration interval, wherein a first signal has a first frequency, a second signal has a second frequency, a third signal is a predefined signal - and wherein the correlation is performed between o the third Signal and one from one

Multiplication of the first signal with the second signal resulting signal, or o the first signal and one from a

Multiplication of the third signal resulting signal with the second signal, characterized in that - the second signal is changed during the integration interval and the correlator unit uses the signal resulting from the multiplication for the integration.

16. Correlator unit according to claim 15, characterized in that the predefined third signal consists of a code, the code has a code rate, - the code rate is changed during the time interval and the correlator unit uses the third signal changing during the integration interval for the integration.

17. Correlator unit according to claim 15, characterized in that the correlator unit has hardware correlators.

18. Correlator unit according to claim 15, characterized in that the correlator unit has means for performing the correlation via an optimum filter or via a Fourier transformation.

19. A signal processing unit for processing signals, wherein a first signal has a first frequency, a second signal has a second frequency, a third signal is a predefined signal comprising a frequency multiplying unit for

Multiplying the first and third signals by the second signal, a correlator for correlating the one of

Multiplication resulting signal with the third and first signal, a frequency changing unit for changing the second frequency, characterized in that the frequency changing unit has means to the second frequency during a temporal

To change intervals and

- The frequency multiplier unit comprises means for changing the first and third frequency with the second during the time interval

Multiply frequency and pass it to the correlator.

20. The signal processing unit according to claim 19, wherein the third signal is a code and has a code rate, additionally comprising a frequency changing unit for changing the code rate of the third signal.

Signal processing unit according to claim 20, characterized in that the frequency changing unit for changing the second frequency and the frequency changing unit for changing the code rate each comprise a frequency change determining unit which determines the magnitude and direction of the change of frequency by values of acceleration and dynamic terms of higher order.

22. The signal processing unit according to claim 21, characterized in that the signal processing unit has a sensor data interface that sends motion data to the frequency change determination unit.

23. Signal processing unit according to claim 19, characterized in that the signal processing unit is used to acquire the first signal.

24. Signal processing unit according to claim 19, characterized in that the signal processing unit is used to track the first signal.

25. A receiver, characterized in that the receiver comprises a signal processing unit according to claim 23 and / or a signal processing unit according to claim 24.

26. A receiver according to claim 25, characterized in that the receiver has a motion data receiver that sends motion data to the sensor data interface.