Method and device for estimating a frequency in the acquisition of a spread-spectrum code signal
View Patent ↗In a method for estimating a frequency deviation between a received spread-spectrum code signal and a local frequency signal, the received spread-spectrum code signal is despread using a local spread-spectrum code. The despread signal is integrated over a particular integration period. From at least two successively obtained integration values, a phase change value characteristic of the phase change between the two integration values is calculated. From this, the frequency deviation is determined.
1. A method for estimating a frequency deviation between a received spread-spectrum code signal and a local frequency signal in the acquisition of the received spread-spectrum code signal in a CDMA receiver, comprising:
generating a frequency-shifted spread-spectrum code signal from the received spread-spectrum code signal by downconverting the received spread-spectrum code signal by the local frequency signal;
despreading the frequency-shifted spread-spectrum code signal using a local spread-spectrum code;
repeated coherent integrating of the despread frequency-shifted spread-spectrum code signal over an integration period, thereby forming a sequence of complex integration values; and
evaluating at least two of the sequence of complex integration values by calculating a phase change value characteristic of a phase change between the at least two of the sequence of complex integration values to determine the frequency deviation by calculating the frequency deviation based on the phase change value characteristic,
wherein calculating the phase change value characteristic comprises multiplying one complex integration value by the complex conjugate of the other complex integration value.
2. The method of claim 1 , wherein the signal acquisition method is used in the CDMA receiver of a satellite positioning system.
3. The method of claim 1 , wherein calculating the frequency deviation from the phase change value characteristic comprises applying an argument function to a complex-valued argument dependent on the phase change value characteristic.
4. The method of claim 1 , wherein calculating the frequency deviation from the phase change value characteristic comprises applying an arc tan function to a complex-valued argument dependent on the phase change value characteristic and a signum function to an argument dependent on the phase change value characteristic.
5. The method of claim 1 , wherein calculating the phase change value characteristic comprises calculating the frequency deviation by averaging over a number of single-frequency deviation calculations, wherein each single-frequency deviation is determined from a phase change value characteristic.
6. The method of claim 1 , further comprising that during calculation of the frequency deviation, determining a received timing of the spread-spectrum code in the received spread-spectrum code signal.
7. The method of claim 1 , wherein the integration period comprises the spread-spectrum code period or a multiple of the spread-spectrum code period.
8. The method of claim 1 , further comprising performing signal sampling before despreading the frequency-shifted spread-spectrum code signal, thereby forming a frequency-shifted spread-spectrum code digital signal.
9. The method of claim 1 , wherein the phase change value is characteristic of a phase change between two of the sequence of complex integration values and is calculated on the basis of these two of the sequence of complex integration values.