Noise distribution shaping for signals, particularly CDMA signals

Abstract

A method is provided for noise distribution shaping of signals, particularly for the application in receivers for CDMA signals. The method includes the acts of generating a blanking control signal by comparing a received signal with at least one blanking threshold, adapting the at least one blanking threshold or the received signal according to an offset value depending on the amplitude of the received signal, and modifying the noise distribution of the received signal by applying blanking of the received signal under control of the blanking control signal.

Claims

1. A method for noise distribution shaping for signals, the method comprising the acts of: generating a blanking control signal by comparing a received signal with at least one blanking threshold; adapting the received signal by adding an offset value depending on an amplitude of the received signal; and modifying the noise distribution of the received signal by applying blanking of the received signal under control of the blanking control signal, wherein the amplitude of the received signal is calculated based on the estimated power P.sub.est of the received signal and the offset value is calculated from the calculated amplitude of the received signal by multiplying a square root of the estimated power P.sub.est with a predefined scaling factor , wherein the predefined scaling factor is positive or negative, constant or time dependent, or a sign of the predefined scaling factor is changeable over time as function of the received signal.

2. The method according to claim 1, wherein the adapting of the received signal according to an offset value depending on the amplitude of the received signal comprises offsetting at least one predefined blanking threshold or the received signal, respectively, with the scaled estimated amplitude of the received signal.

3. The method according to claim 1, wherein the modifying of the noise distribution of the received signal by applying blanking under control of the blanking control signal comprises setting a sample of the received signal to a predefined value depending on the blanking control signal, wherein the predefined value is set to 0 for samples exceeding the blanking thresholds.

4. The method according to claim 1, wherein a set of blanking thresholds is used, the set comprising at least one blanking threshold for each one of a plurality of received signals.

5. The method according to claim 1, wherein the received signal is a CDMA signal, and the offset value is calculated by multiplying the square root of the estimated power P.sub.est with a scaling factor being +1 or 1 depending on the chip values of the CDMA signal.

6. The method according to claim 1, wherein a different blanking threshold is applied at each time instant.

7. The method according to claim 1, wherein the received signal is a signal of interest, and wherein the instantaneous amplitude of the received signal is used to determine the offset value.

8. The method according to claim 1, wherein the adapted blanking threshold is asymmetrical with respect to zero for the received signal.

9. A computer product, comprising a computer readable non-transitory medium having stored thereon program code segments that: generate a blanking control signal by comparing a received signal with at least one blanking threshold; adapt the received signal by adding an offset value depending on an amplitude of the received signal; and modify the noise distribution of the received signal by applying blanking of the received signal under control of the blanking control signal, wherein the amplitude of the received signal is calculated based on the estimated power P.sub.est of the received signal and the offset value is calculated from the calculated amplitude of the received signal by multiplying a square root of the estimated power P.sub.est with a predefined scaling factor , wherein the predefined scaling factor is positive or negative, constant or time dependent, or a sign of the predefined scaling factor is changeable over time as function of the received signal.

10. A device for noise distribution shaping for signals, the device comprising: a memory storing a computer program; a processor configured to execute the computer program to: a comparator circuit configured to generate a blanking control signal by comparing a received signal with at least one blanking threshold; adapt the received signal by adding an offset value depending on an amplitude of the received signal; and modify the noise distribution of the received signal by applying blanking of the received signal under control of the blanking control signal, wherein the processor is further configured to execute the computer program to adapt the received signal by calculating the amplitude of the received signal based on the estimated receive power P.sub.est of the received signal and to calculate the offset value from the calculated amplitude of the received signal by multiplying a square root of the estimated power P.sub.est with a predefined scaling factor , wherein the predefined scaling factor is positive or negative, constant or time dependent, or a sign of the predefined scaling factor is changeable over time as function of the received signal.

11. The device according to claim 10, wherein the comparator circuit comprises a first input for receiving signal samples and at least one second input for receiving the at least one blanking threshold.

12. The device according to claim 10, wherein the processor is further configured to execute the computer program to adapt the received signal according to an offset value depending on the amplitude of the received signal by offsetting at least one predefined blanking threshold or the received signal, respectively, with the scaled estimated amplitude of the received signal.

13. The device according to claim 10, wherein the processor is further configured to execute the computer program to modify the noise distribution of the received signal by setting a sample of the received signal to a predefined value depending on the blanking control signal, wherein the predefined value is set to 0 for samples exceeding the blanking thresholds.

14. The device according to claim 10, wherein the device is configured to use a set of blanking thresholds, wherein the set comprises at least one blanking threshold for each one of a plurality of received signals.

15. The device according to claim 10, wherein the received signal is a CDMA signal, and the means for adapting are configured to calculate the offset value by multiplying the square root of the estimated power P.sub.est with a scaling factor being +1 or 1 depending on the chip values of the CDMA signal.

16. A Global Navigation Satellite System (GNSS) receiver circuitry, comprising; receiving circuitry configured to received Code Division Multiple Access (CDMA) signals; an analog to digital converter for generating samples of the received CDMA signals; a plurality of noise distribution hardware shapers for modifying the noise distribution of the sampled CDMA signals, wherein the modifying of the noise distribution of the sampled CDMA signals is carried out by adapting the received CDMA signals by adding an offset value depending on an amplitude of the respectively received CDMA signals; and a signal processor configured to process the sampled CDMA signals output by the noise distribution shapers and to output chip values of the received CDMA signals, wherein the offset value is calculated by multiplying a square root of an estimated power P.sub.est with a scaling factor being +1 or 1 depending on the chip values of the received CDMA signals.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 shows an embodiment of a GNSS receiver circuitry with a noise distribution shaper according to the invention;

(2) FIG. 2 shows a flow chart of an embodiment of a noise distribution shaping method for CDMA signals according to the invention; and

(3) FIG. 3 shows a diagram with different adapted blanking thresholds

DESCRIPTION OF PREFERRED EMBODIMENTS

(4) In the following, functionally similar or identical elements may have the same reference numerals. Absolute values are shown below by way of example only and should not be construed as limiting the invention. Even if the following description is applied to CDMA signals of a GNSS, it should be noted that the invention can generally be applied to any kind of signal and is, therefore, not restricted to CDMA signals.

(5) FIG. 1 shows a block diagram of a GNSS receiver circuitry 10 comprising a noise distribution shaper according to embodiments of the invention. The shown circuitry 10 comprises a RF front end circuitry 14 for filtering and down converting CDMA signals received from GNSS signals into a baseband for further processing, an ADC (Analog to Digital Converter) 16 for sampling the down converted CDMA signals and converting the analog samples of the CDMA signals into digital values, a noise distribution shaper 18 for shaping the noise distribution of the digitized CDMA signal samples of one of the plurality of the received CDMA signals, and a GNSS signal processor 26 for correlating the received CDMA signals with spreading sequences or chip values used to encode the CDMA signals and processing the CDMA signals for determining and outputting positioning data 28. It should be noted that the noise distribution shaping can also be applied directly in RF, and is therefore not restricted to the baseband as described above.

(6) In the following, the implementation of the noise distribution shaper 18 is described in detail. The digitized CDMA samples output by the ADC 16 are input to a blanker 20 and an input of a comparator circuit 22. The comparator circuit 22 further receives a first adaptive blanking threshold BTH(i) and a second adaptive blanking threshold BTH+(i), which are both output from a blanking threshold generator 24. The adaptive blanking thresholds BTH(i) and BTH+(i) are assigned to one signal (index i) of the plurality of the received I CDMA signals. In other words, each received CDMA signal usually has its own dedicated adaptive blanking thresholds. Also, less or more than two adaptive blanking thresholds may be provided. Furthermore, for each chip value taken at instant k, the blanking thresholds BTH(i) and BTH+(i) will be modified according to this binary chip value. Now the time dependency is considered implicitly in the example to ease readability.

(7) The blanking threshold generator 24 receives from the GNSS signal processor 26 the chip values, which are used by the processor to decode and despread the received CDMA signals. For example, if the processor 26 is able to decode four (I=4) CDMA signals among the plurality of received CDMA signals, it outputs the four chip values corresponding to the spreading sequences assigned to the four received CDMA signals and used to decode them by the processor 26. It should be noted that in such case four different adaptive blanking threshold generators 24 are required since each block will be adapted to the chip value of each sequence (in FIG. 1, only one generator block 24 is shown).

(8) The blanking threshold generator 24 generates with the received chip values the first adaptive blanking threshold BTH(i) and the second adaptive blanking threshold BTH+(i). The blanking thresholds BTH+(i) and BTH(i) may be generated by offsetting predefined blanking thresholds BTH.sub.pre+ and BTH.sub.pre with the scaled amplitude of the respective CDMA signal i. The amplitude of the offset applied to the predefined blanking thresholds BTH.sub.pre+ and BTH.sub.pre is calculated based on the estimated power (P.sub.est) of the received signal based on the samples provided by the Analog to Digital Converter (ADC), from block 16, multiplied with a scaling factor, which is a function of the binary chip value. Two scaling factors + and are respectively deduced from the positive and negative chip value. The predefined blanking thresholds BTH.sub.pre+ and BTH.sub.pre may be, for example, selected depending on the environment of operation of the GNSS receiver and particularly be configured depending on the occurrence of pulsed interferences such as generated by vehicle ignition systems, power lines, heavy current switches or microwave ovens. For example, in an environment with strong pulsed interferences, such as in the neighborhood of vehicle ignition systems or power lines, the predefined blanking thresholds may be selected with a higher value than in environments with weaker pulsed interferences. For the selection of predefined blanking thresholds suitable for a certain environment, the strength and frequency of occurrence of pulsed interferences in the received CDMA signals may be determined, and depending thereon suitable predefined blanking thresholds may be determined.

(9) The offsetting of the predefined blanking thresholds BTH.sub.pre+ and BTH.sub.pre may comprise adding the estimated received power P.sub.est multiplied with a positive scaling factor .sub.+ for positive chip value, or adding the estimated received power P.sub.est multiplied with a negative scaling factor .sub. for negative chip value:

(10) Hence for positive chip values the adapted blanking thresholds are given by:
(BTH.sub.pre)+.sub.+(i)(sqrt(P.sub.est)).fwdarw.BTH(i)
(BTH.sub.pre+)+.sub.+(i)(sqrt(P.sub.est)).fwdarw.BTH+(i)

(11) And for negative chip values the adapted blanking thresholds are given by:
(BTH.sub.pre)+.sub.(i)(sqrt(P.sub.est)).fwdarw.BTH(i)
(BTH.sub.pre+)+.sub.(i)(sqrt(P.sub.est)).fwdarw.BTH+(i)

(12) The adaptive blanking thresholds BTH+(i) and BTH(i) are sent to second inputs of the comparator circuit 22, which receives on its first input the digitized CDMA samples from the ADC 16. The comparator circuit 22 compares the amplitudes (algebraic values) of the digitized CDMA samples with the adaptive blanking thresholds BTH+(i) and BTH(i) and generates, depending on the comparison, a blanking control signal NBCTRL(i), which controls the blanker 20.

(13) The comparator circuit 22 may generate the blanking control signal NBCTRL(i) for example as follows:
amplitudes of CDMA samples of CDMA signal i>BTH+(i).fwdarw.NBCTRL(i)=+1
amplitudes of CDMA samples of CDMA signal i<BTH(i).fwdarw.NBCTRL(i)=1
amplitudes of CDMA samples of CDMA signal i<BTH+(i) and >BTH(i).fwdarw.NBCTRL(i)=0

(14) The blanker 20 sets the samples of the CDMA signals received at its input to a predefined value such as zero as long as the noise blanking control signal NBCTRL(i) is +1 or 1, and passes the received digitized CDMA signals from its input to its output if the blanking control signal NBCTRL(i) is 0.

(15) The above example is given for two blanking thresholds BTH+ and BTH (N=2). In the following, a brief example for the case of a larger N=4 for a CDMA signal i is given (hereby BTH(n, i) means blanking threshold n for CDMA signal i):
CDMA signal i Amplitude<BTH(1,i).fwdarw.NBCTRL(i)=+1.
BTH(1,i)<CDMA signal i Amplitude<BTH(2,i).fwdarw.NBCTRL(i)=0.
BTH(2,i)<CDMA signal i Amplitude<BTH(3,i).fwdarw.NBCTRL(i)=+1.
CDMA signal i Amplitude>BTH(4,i).fwdarw.NBCTRL(i)=+1.

(16) Again, the proposed control low for the NBCTRL(i) based on a comparison with the 4 thresholds is just one example. The blanking control signal for the blanking thresholds BTH(n, i) is adapted for the i.sup.th tracked CDMA signal among I signals. As a consequence, as many blanking blocks as there are tracked signals (I) are required. Alternatively, a single control block fed with the different chip values for the I CDMA signals can be provided. However, this single control block must then be able to handle the blanking thresholds BTH(n, i) for the i CDMA signal, for example by applying multiplexing inside the block.

(17) FIG. 2 shows a flowchart of a method for noise distribution shaping for I CDMA signals according to embodiments of the invention, which can be implemented as a computer program to be executed by a processor. The method receives in step S0 digitized CDMA signal samples of the i.sup.th CDMA signal from the ADC 16. In step S12, the chip values of the i.sup.th CDMA signal are provided, which are known a priori and stored in a memory. In step S13 the i.sup.th CDMA signal from the ADC 16 is provided in order to estimate the power of the i.sup.th received CDMA signal. The scaled estimated chip amplitudes are then used in step S4 to offset predefined blanking thresholds BTH.sub.pre(i) to generate a set of blanking thresholds BTH(i) for each CDMA signal i. With the set of blanking thresholds BTH(i) and the received digitized CDMA signal samples, the method generates, in step S10, a blanking control signal for each CDMA signal i, for example by a comparison as described above. In step S16, the noise distribution of the received samples of the i.sup.th CDMA signal is shaped by a blanking process controlled by the i.sup.th blanking control signals generated in step S10. The CDMA signal samples with shaped noise distribution are finally output to the GNSS signal processor 26 for further processing.

(18) FIG. 3 shows a diagram with two different adapted blanking thresholds BTH.sub.pre+{square root over (P)} and BTH.sub.pre++{square root over (P)} in case the chip value is positive. The blanking thresholds BTH.sub.pre and BTH.sub.pre+ are adapted with the estimated power of a received CDMA signal x(t) scaled by a coefficient (in this example =.sub.+=1 since the chip value c.sup.1(t) is positive). In the baseline situation, the coefficient shall be the square root of the estimated power multiplied with binary chip value {square root over (P)} of the received CDMA signal. Generally, this coefficient might be different, and it can even be different for the positive and negative blanking threshold as shown in FIG. 3.

(19) The present invention allows reducing the degradation of the SNIR of a received signal, particularly a CMDA signal, when there are no pulsed interferences by offsetting the blanking thresholds or the signal depending on the amplitude of the signal, for example with the scaled amplitude (the amplitude can be positive or negative according to the chip value) of a received CDMA signal, and by comparing the amplitude (algebraic value) of samples of the received signal to the blanking thresholds.

REFERENCE NUMERALS AND ACRONYMS

(20) 10 GNSS receiver circuitry 12 antenna 14 RF front end circuitry 16 ADC 18 noise distribution shaper 20 blanker 22 comparator circuit 24 blanking threshold generator 26 GNSS signal processor 28 GNSS output data ADC Analog to Digital Converter BTH Blanking Threshold CDMA Code Division Multiple Access GNSS Global Navigation Satellite System NBCTRL Noise Blanking Control RF Radio Frequency

(21) The foregoing disclosure has been set forth merely to illustrate the invention and is not intended to be limiting. Since modifications of the disclosed embodiments incorporating the spirit and substance of the invention may occur to persons skilled in the art, the invention should be construed to include everything within the scope of the appended claims and equivalents thereof.