Receiving spread spectrum signals

• US 10,177,950 B2
• Filed: 08/09/2017
• Issued: 01/08/2019
• Est. Priority Date: 08/11/2016
• Status: Active Grant

• Current Assignee: Airbus DS GMBH
• Original Assignee: Airbus DS GMBH
• Inventors: Floch, Jean-Jacques, Soualle, Francis
• Primary Examiner(s): Wong, Linda
• Application Number:
  US15/672,371
• Publication Number:
  US 20180048502A1
• Time in Patent Office: 517 Days
• Field of Search: 375130, 375132, 375134, 375135, 375136, 375137, 375140, 375142, 375141, 375133, 375144, 375145, 375146, 375147, 375149, 375150, 375152, 375143, 375219, 375220, 375221, 375222, 375240, 37524026, 37524028, 37524027, 375259, 375285, 375284, 375278, 375293, 375295, 375316, 375340, 375338, 375346, 375347, 375350, 375326, 375324, 375354, 375362, 375365, 375366, 375367, 375368
• CPC Class Codes: G01S 19/01 Satellite radio beacon positioning systems transmitting time-stamped messages, e.g. GPS [Global Positioning System], GLONASS [Global Orbiting Navigation Satellite System] or GALILEO
• CPC Class Codes: G01S 19/30 code related G01S19/246 takes precedence
• CPC Class Codes: G06F 17/15 Correlation function computation including computation of convolution operations arithmetic circuits for sum of products per se, e.g. multiply-accumulators G06F7/5443; digital filters, e.g. FIR, IIR, adaptive filters H03H17/00
• CPC Class Codes: H04B 1/692 Hybrid techniques using combinations of two or more spread spectrum techniques
• CPC Class Codes: H04B 1/707 using direct sequence modulation
• CPC Class Codes: H04B 2001/6904 using code hopping
• CPC Class Codes: H04B 2001/6908 using time hopping
• CPC Class Codes: H04B 2001/6912 using chirp
• CPC Class Codes: H04B 2001/70706 using a code tracking loop, e.g. a delay locked loop
• CPC Class Codes: H04L 27/2278 using correlation techniques, e.g. for spread spectrum signals
• CPC Class Codes: H04L 27/2637 with direct modulation of individual subcarriers

Abstract

A receiver for spread spectrum signals comprising a first part for preprocessing and digitizing a received signal, and a second part for tracking the digitized signal comprising a carrier loop and a code loop. The code loop comprises a generator for a reference receiver signal for correlation with the received signal and the code loop is configured to modify the reference signal to shape a correlation function between the received signal and the reference receiver signal. The first part is adapted to multiply the received spread spectrum signal with a first analog spectral offsetting signal provided for down-converting the received signal to an intermediate frequency and a sub-carrier frequency, selected from a set of sub-carrier frequencies, such that the received signal is down-converted and spectrally offset in the analog domain during a time interval covering at least one chip of a spreading code of the received signal.

Claims

1. A receiver for spread spectrum signals comprising a first part configured to preprocess and digitize a received spread spectrum signal, and

a second part configured to track the digitized received spread spectrum signal and comprising a carrier loop and a code loop, wherein the code loop comprises a generator for a reference receiver signal for correlation with the received spread spectrum signal and the code loop is configured to modify the reference receiver signal in order to shape a correlation function between the received spread spectrum signal and the reference receiver signal,

wherein one of

the first part is adapted for multiplying the received spread spectrum signal with a first analog spectral offsetting signal provided for down-converting the received spread spectrum signal to an intermediate frequency IF0 and a sub-carrier frequency f_m selected from a set of M sub-carrier frequencies such that the received spread spectrum signal is down-converted and spectrally offset in the analog domain during a time interval covering L_m chips, wherein L_m chips comprises at least one chip of a spreading code of the received spread spectrum signal,

or

the first part is adapted for multiplying the received spread spectrum signal with a second analog spectral offsetting signal provided for down-converting the received spread spectrum signal to an intermediate frequency IF0 in the analog domain, for digitizing the down-converted received spread-spectrum signal, and for multiplying the digitized and down-converted received spread spectrum signal with a digital spectral offsetting signal provided for spectrally offsetting the digitized and down-converted received spread spectrum signal in the digital domain to a sub-carrier frequency f_m selected from a set of M sub-carrier frequencies such that the digitized and down-converted received spread spectrum signal is spectrally offset in the digital domain during a time interval covering L_m chips, wherein L_m chips comprises at least one chip of a spreading code of the received spread spectrum signal.

2. The receiver of claim 1, wherein several spectral offsettings in the analog domain or in the digital domain are performed with different sub-carrier frequencies, f_m, and/or the time interval covering L_m chips varies from cycle to cycle of a frequency offsetting cycle C covering M sub-carrier frequencies {f_m}_1≤

m≤

M,C.

3. The receiver of claim 1, wherein the first analog spectral offsetting signal is defined by e^j(2π

(f<sup>RF+IF0+fm)(t−

τ

est,prec)+φ

m)</sup>, and the second analog spectral offsetting signal is defined by e<sup>j(2π

(fRF+IF0)(t−

τ

est,prec))</sup> and the digital spectral offsetting signal is defined by e<sup>j(2π

(fm)(t−

τ

est,prec)+φ

m)</sup>

with t being a time variable,

f_m being a sub-carrier frequency selected from the set of M sub-carrier frequencies and applied during a time interval covering L_m chips,

τ

_est,prec being a time offset, which is used for synchronization and depends on the actual propagation delay τ

of the transmitted signal up to the receiver and is estimated in a τ

_est,prec generator from at least one of the past outputs of the code loop and/or the carrier loop of the receiver, and/or is estimated by an external estimator of the propagation delay to the receiver and processed by the τ

_est,prec generator, and

φ

m being a phase which ensures that the argument of the exponential term is continuous at a transition between two consecutive time intervals corresponding to two sub-carrier frequencies f_m and f_m+1.

4. The receiver of claim 1, wherein the first part comprises a local oscillator, an analog digital converter and either a frequency generator configured for synthesizing frequency references for the local oscillator for down-converting the received spread spectrum signal to the intermediate frequency IF₀ and the sub-carrier frequency f_m and for the analog digital converter for digitizing the down-converted received spread spectrum signal, or a frequency generator configured for synthesizing frequency references for the local oscillator for down-converting the received spread spectrum signal to the intermediate frequency IF₀ and for the analog digital converter for digitizing the down-converted received spread spectrum signal and an additional digital local oscillator to spectrally offset the down-converted digital spread spectrum signal to the sub-carrier frequency f_m.

5. The receiver of claim 1, wherein the first part comprises a pre-processing unit for pre-processing the received spread spectrum signal before digitizing, wherein the pre-processing unit comprises filtering and an automatic gain control of the received spread spectrum signal.

6. The receiver of claim 1 being configured to receive as spread spectrum signal a signal with any pulse shape type such that the combination of the reference receiver signal multiplied with the offsetting signal can be replaced with a Binary Offset carrier (BOC) (K,N) reference receiver signal if the set of M sub-carrier frequencies contains only 2 frequencies +f_K and −

f_K and the duration of the time intervals when +f_k is applied is identical to the duration of the time intervals when −

f_k is applied.

7. The receiver of claim 6, wherein the receiver is configured to receive as spread spectrum signal a Binary-Phase-Shift-Keying—

BPSK(N)—

modulated spread spectrum signal.

8. A device for positioning using spread spectrum signals transmitted by a Global Navigation Satellite System, the device comprising a receiver of claim 1 for receiving the spread spectrum signals.

9. A method for receiving spread spectrum signals comprising the following steps:

preprocessing and digitizing a received spread spectrum signal,

tracking the digitized received spread spectrum signal by means of a carrier loop and a code loop, wherein the tracking comprises generating a reference receiver signal for correlation with the received spread spectrum signal in the code loop and shaping a correlation function between the received spread spectrum signal and the reference receiver signal by modifying the reference receiver signal in the code loop,

wherein one of

the received spread spectrum signal is multiplied with a first analog spectral offsetting signal provided for down-converting the received spread spectrum signal to an intermediate frequency IF₀ and a sub-carrier frequency f_m selected from a set of M sub-carrier frequencies such that the received spread spectrum signal is down-converted and spectrally offset in the analog domain during a time interval covering L_m chips, wherein L_m chips comprises at least one chip of a spreading code of the received spread spectrum signal,

or

the received spread spectrum signal is multiplied with a second analog spectral offsetting signal provided for down-converting the received spread spectrum signal to an intermediate frequency IF₀ in the analog domain, for digitizing the down-converted received spread-spectrum signal, and for multiplying the digitized and down-converted received spread spectrum signal with a digital spectral offsetting signal provided for spectrally offsetting the digitized and down-converted received spread spectrum signal in the digital domain to a sub-carrier frequency f_m selected from a set of M sub-carrier frequencies such that the digitized and down-converted received spread spectrum signal is spectrally offset in the digital domain during a time interval covering L_m chips, wherein L_m chips comprises at least one chip of a spreading code of the received spread spectrum signal;

wherein the first analog spectral offsetting signal is defined by e<sup>j(2π

(fRF+IF0+fm)(t−

τ

est,prec)+φ

m)</sup>, and the second analog spectral offsetting signal is defined by e<sup>j(2π

(fRF+IF0)(t−

τ

est,prec))</sup> and the digital spectral offsetting signal is defined by e<sup>j(2π

(fm)(t−

τ

est,prec)+φ

m)</sup>

with t being a time variable,

f_m being a sub-carrier frequency selected from the set of M sub-carrier frequencies and applied during a time interval covering L_m chips,

τ

_est,prec being a time offset, which is used for synchronization and is a function of the actual propagation delay τ

of the transmitted signal up to the receiver and is estimated in a τ

_est,prec generator from at least one of the past outputs of the code loop and/or carrier loop of the receiver, and/or is estimated by an external estimator of the propagation delay to the receiver and processed by the τ

_est,prec generator, and

φ

m being a phase which ensures that the argument of the exponential term is continuous at a transition between two consecutive sub-carrier frequencies f_m and f_m+1.

10. The method of claim 9, wherein several spectral offsettings in the analog domain or in the digital domain are performed with different sub-carrier frequencies, f_m, and/or the time interval covering L_m chips varies from cycle to cycle of a frequency offsetting cycle C covering M sub-carrier frequencies {f_m}_1≤

m≤

M,C.

11. The method of claim 9, wherein the step of preprocessing comprises filtering and an automatic gain control of the received spread spectrum signal.

12. A method for receiving spread spectrum signals comprising the following steps:

preprocessing and digitizing a received spread spectrum signal,

tracking the digitized received spread spectrum signal by means of a carrier loop and a code loop, wherein the tracking comprises generating a reference receiver signal for correlation with the received spread spectrum signal in the code loop and shaping a correlation function between the received spread spectrum signal and the reference receiver signal by modifying the reference receiver signal in the code loop,

wherein one of

the received spread spectrum signal is multiplied with a first analog spectral offsetting signal provided for down-converting the received spread spectrum signal to an intermediate frequency IF₀ and a sub-carrier frequency f_m selected from a set of M sub-carrier frequencies such that the received spread spectrum signal is down-converted and spectrally offset in the analog domain during a time interval covering L_m chips, wherein L_m chips comprises at least one chip of a spreading code of the received spread spectrum signal,

or

the received spread spectrum signal is multiplied with a second analog spectral offsetting signal provided for down-converting the received spread spectrum signal to an intermediate frequency IF₀ in the analog domain, for digitizing the down-converted received spread-spectrum signal, and for multiplying the digitized and down-converted received spread spectrum signal with a digital spectral offsetting signal provided for spectrally offsetting the digitized and down-converted received spread spectrum signal in the digital domain to a sub-carrier frequency f_m selected from a set of M sub-carrier frequencies such that the digitized and down-converted received spread spectrum signal is spectrally offset in the digital domain during a time interval covering L_m chips, wherein L_m chips comprises at least one chip of a spreading code of the received spread spectrum signal, wherein the steps of down-converting and digitizing of the received spread spectrum signal comprises either the synthesizing of frequency references for down-converting the received spread spectrum signal to the intermediate frequency IF₀ and the sub-carrier frequency f_m and for digitizing the down-converted received spread spectrum signal, or the synthesizing of frequency references for down-converting the received spread spectrum signal to the intermediate frequency IF₀ and for digitizing the down-converted received spread spectrum signal and for spectrally offsetting the down-converted digital spread spectrum signal to the sub-carrier frequency fm.

13. The method of claim 12, wherein several spectral offsettings in the analog domain or in the digital domain are performed with different sub-carrier frequencies, f_m, and/or the time interval covering L_m chips varies from cycle to cycle of a frequency offsetting cycle C covering M sub-carrier frequencies {f_m}_1≤

m≤

M,C.

14. The method of claim 12, wherein the step of preprocessing comprises filtering and an automatic gain control of the received spread spectrum signal.

15. A method for receiving spread spectrum signals comprising the following steps:

preprocessing and digitizing a received spread spectrum signal,

tracking the digitized received spread spectrum signal by means of a carrier loop and a code loop, wherein the tracking comprises generating a reference receiver signal for correlation with the received spread spectrum signal in the code loop and shaping a correlation function between the received spread spectrum signal and the reference receiver signal by modifying the reference receiver signal in the code loop,

wherein one of

the received spread spectrum signal is multiplied with a first analog spectral offsetting signal provided for down-converting the received spread spectrum signal to an intermediate frequency IF₀ and a sub-carrier frequency f_m selected from a set of M sub-carrier frequencies such that the received spread spectrum signal is down-converted and spectrally offset in the analog domain during a time interval covering L_m chips, wherein L_m chips comprises at least one chip of a spreading code of the received spread spectrum signal,

or

the received spread spectrum signal is multiplied with a second analog spectral offsetting signal provided for down-converting the received spread spectrum signal to an intermediate frequency IF₀ in the analog domain, for digitizing the down-converted received spread-spectrum signal, and for multiplying the digitized and down-converted received spread spectrum signal with a digital spectral offsetting signal provided for spectrally offsetting the digitized and down-converted received spread spectrum signal in the digital domain to a sub-carrier frequency f_m selected from a set of M sub-carrier frequencies such that the digitized and down-converted received spread spectrum signal is spectrally offset in the digital domain during a time interval covering L_m chips, wherein L_m chips comprises at least one chip of a spreading code of the received spread spectrum signal, wherein as spread spectrum signal a signal with any pulse shape type and particularly a Binary-Phase-Shift-Keying—

BPSK(N)—

modulated spread spectrum signal such that the combination of the reference receiver signal multiplied with the offsetting signal can be replaced with a Binary Offset Carrier (BOC) (K,N) reference receiver signal if the set of M sub-carrier frequencies contains only 2 frequencies +f_K and −

f_K and the duration of the time intervals when +f_k is applied is identical to the duration of the time intervals when −

f_k is applied, is received.

16. The method of claim 15, wherein several spectral offsettings in the analog domain or in the digital domain are performed with different sub-carrier frequencies, f_m, and/or the time interval covering L_m chips varies from cycle to cycle of a frequency offsetting cycle C covering M sub-carrier frequencies {f_m}_1≤

m≤

M,C.

17. The method of claim 15, wherein the step of preprocessing comprises filtering and an automatic gain control of the received spread spectrum signal.