Method and arrangement for reducing frequency offset in a radio receiver

• US 6,956,895 B2
• Filed: 05/24/2001
• Issued: 10/18/2005
• Est. Priority Date: 05/30/2000
• Status: Expired due to Term

• Current Assignee: Nokia Technologies Oy (Nokia Corporation)
• Original Assignee: Nokia Mobile Phones UK Limited (Nokia Corporation)
• Inventors: Vihriälä, Jaakko
• Primary Examiner(s): Le, Amanda T.
• Assistant Examiner(s): WARE, CICELY Q
• Application Number:
  US09/864,984
• Publication Number:
  US 20020045433A1
• Time in Patent Office: 1,608 Days
• Field of Search: 375147-150, 370/342, 455296-313
• US Class Current: 375/148
• CPC Class Codes: H03J 7/00 Automatic frequency control; Automatic scanning over a band of frequencies
• CPC Class Codes: H04B 1/707 using direct sequence modulation

Abstract

The invention concerns generally the technology of reducing frequency offset in a radio receiver. Especially the invention concerns receivers where a channel estimator is used for correcting the base band signal. The objects of the invention are achieved by monitoring the phase of the channel estimation output and generating a complex phasor on the basis of successive phase values. The received baseband signal is then multiplied by the generated complex phasor for compensating the frequency offset. The frequency compensation can be made before or after said channel estimation thus producing a feedback compensation or feed forward compensation. The feedback compensation can be implemented by compensating the baseband signal either prior to the despreading or after the despreading.

Claims

1. A method for compensating a frequency offset in processing a received radio signal, wherein the receiving and the processing comprises:

(a) receiving a radio signal having a carrier frequency from a radio channel,

(b) producing a local oscillator signal, wherein there is a frequency offset between the carrier frequency of the received radio signal and the frequency of the local oscillator signal,

(c) mixing the received radio signal with the local oscillator signal for producing a baseband signal,

(d) converting the baseband signal into digital samples,

(e) producing a radio channel estimation data,

(f) correcting the phase of the baseband signal on the basis of the channel estimation data,

(g) detecting phases from successive channel estimation data,

(h) generating a complex phasor on the basis of said detected phases,

(i) multiplying the baseband signal with said complex phasor for reducing the frequency offset of the baseband signal

(j) producing a first channel estimation data,

(k) detecting phases from successive first channel estimation data,

(l) generating a complex phasor on the basis of said detected phases from successive first channel estimation data,

(m) multiplying the baseband signal with the complex phasor for correcting the frequency offset,

(n) producing a second channel estimation data on the basis of the frequency corrected signal, and

(o) multiplying an uncorrected baseband signal with the second channel estimate data for forming a corrected output signal.

2. A method according to claim 1, characterized in that the received signal is a spread spectrum signal and the method further comprises the step of despreading the received wideband signal to form a narrowband signal.

3. A method according to claim 2, characterized in that the step of multiplying the baseband signal with said complex phasor is performed to the wideband signal prior to despreading.

4. A method according to claim 2, characterized in that the received signal is a spread spectrum signal and the step of multiplying the baseband signal with said complex phasor is performed to the narrowband signal after despreading.

5. A method according to claim 1, characterized in that the radio channel estimate data is made on the basis of the baseband signal that has been multiplied with a complex phasor for frequency offset correction.

6. A method according to claim 5, characterized in that before the step of detecting phases the method comprises a step of forming a derivative signal on the basis of successive channel estimate data, and a step of low pass filtering the derivated data.

7. A method according to claim 5, characterized in that the after the step of detecting phases the method comprises a step of forming a phase derivative signal on the basis of successive detected phase values, and a step of low pass filtering the derivated data.

8. A method according to claim 5, characterized in that before the step of generating a complex phasor on the basis of said detected phases the method further comprises a step of integrating.

9. A method according to claim 1, characterized in that the after the step of detecting phases the method comprises a step of forming a phase derivative signal on the basis of successive detected phase values.

10. A method according to claim 1, characterized in that the before the step of detecting phases the method comprises a step of forming a phase derivative signal on the basis of successive channel estimate data.

11. A method according to claim 1, characterized in that the processing the baseband signal is made for at least two multipath components of the received signal, and the process of reducing the frequency offset is based on averaging at least one signal from the processing of the different multipath components.

12. A method according to claim 11, characterized in that the complex phasor is generated on the basis of frequency offset estimate values from at least two multipath components.

13. An arrangement for receiving a radio signal and compensating a frequency offset in processing the received radio signal, wherein the arrangement comprises:

(a) means for receiving a radio signal having a carrier frequency from a radio channel,

(b) means for producing a local oscillator signal, wherein there is a frequency offset between the carrier frequency of the received radio signal and the frequency of the local oscillator signal,

(c) means for mixing the received radio signal with the local oscillator signal for producing a baseband signal,

(d) means for converting the baseband signal into digital samples,

(e) means for producing a radio channel estimation data,

(f) means for correcting the phase of the baseband signal on the basis of the channel estimation data,

(g) means for detecting phases from successive channel estimation data,

(h) means for generating a complex phasor on the basis of said detected phases,

(i) means for multiplying the baseband signal with said complex phasor for reducing the frequency offset of the baseband signal

(j) means for producing a first channel estimation data,

(k) means for detecting phases from successive first channel estimation data,

(l) means for generating a complex phasor on the basis of said detected phases from successive first channel estimation data,

(m) means for multiplying the base band signal with the complex phasor for correcting the frequency offset,

(n) means for producing a second channel estimation data on the basis of the frequency corrected signal, and

(o) means for multiplying an uncorrected baseband signal with the second channel estimate data for forming a corrected output signal.

14. An arrangement according to claim 13, characterized in that the received signal is a spread spectrum signal and the arrangement further comprises means for despreading the received wideband signal to form a narrowband signal.

15. An arrangement according to claim 14, characterized in that the arrangement comprises means for multiplying a wideband baseband signal with said complex phasor with the output coupled to the input of said despreading means.

16. An arrangement according to claim 14, characterized in that the arrangement comprises means for multiplying a narrowband baseband signal with said complex phasor with the input coupled to the output of the despreading means.

17. An arrangement according to claim 13, characterized in that input of the means for forming the radio channel estimate data is coupled to the output of said means for multiplying the baseband signal with said complex phasor for reducing the frequency offset of the baseband signal.

18. An arrangement according to claim 13, characterized in that it comprises a derivator that is coupled to the output of said channel estimator and a low pass filter which has an input coupled to the output of said derivator and an output coupled to the input of said means for detecting phases.

19. An arrangement according to claim 13, characterized in that it comprises a derivator that is coupled to the output of said means for detecting phases, and a low pass filter which has an input coupled to the output of said derivator and an output coupled to the input of said means for forming a complex phasor.

20. An arrangement according to claim 13, characterized in comprises an integrator for integrating the phase detected data, to form an error frequency value for the input of the means for forming a complex phasor.

21. An arrangement according to claim 13, characterized in that it comprises a derivator for forming a phase derivative signal on the basis of successive detected phase values.

22. An arrangement according to claim 13, characterized in that it comprises a derivator with its input coupled to the output of said channel estimation means and for forming a derivative signal on the channel estimation data prior to detecting phases.

23. An arrangement according to claim 14, characterized in that it comprises at least two rake fingers, and means for averaging at least one corresponding signal from the at least two rake fingers for the process of reducing the frequency offset.

24. A method according to claim 14, characterized in that it comprises means for generating the complex phasor on the basis of frequency offset estimate values (fe) from the at least two rake fingers.

25. A mobile station including an arrangement for receiving a radio signal and compensating a frequency offset in processing the received radio signal, wherein the arrangement comprises:

(a) means for receiving a radio signal having a carrier frequency from a radio channel,

(b) means for producing a local oscillator signal, wherein there is a frequency offset between the carrier frequency of the received radio signal and the frequency of the local oscillator signal,

(c) means for mixing the received radio signal with the local oscillator signal for producing a baseband signal,

(d) means for converting the baseband signal into digital samples,

(e) means for producing a radio channel estimation data,

(f) means for correcting the phase of the baseband signal on the basis of the channel estimation data,

(g) means for detecting phases from successive channel estimation data,

(h) means for generating a complex phasor on the basis of said detected phases, and

(i) means for multiplying the baseband signal with said complex phasor for reducing the frequency offset of the baseband signal,

(j) means for producing a first channel estimation data,

(k) means for detecting phases from successive first channel estimation data,

(l) means for generating a complex phasor on the basis of said detected phases from successive first channel estimation data,

(m) means for multiplying the baseband signal with the complex phasor for correcting the frequency offset,

(n) means for producing a second channel estimation data on the basis of the frequency corrected signal, and

(o) means for multiplying an uncorrected baseband signal with the second channel estimate data for forming a corrected output signal.

26. A base station including an arrangement for receiving a radio signal and compensating a frequency offset in processing the received radio signal, wherein the arrangement comprises:

(a) means for receiving a radio signal having a carrier frequency from a radio channel,

(b) means for producing a local oscillator signal, wherein there is a frequency offset between the carrier frequency of the received radio signal and the frequency of the local oscillator signal,

(c) means for mixing the received radio signal with the local oscillator signal for producing a baseband signal,

(d) means for converting the baseband signal into digital samples,

(e) means for producing a radio channel estimation data,

(f) means for correcting the phase of the baseband signal on the basis of the channel estimation data,

(g) means for detecting phases from successive channel estimation data,

(h) means for generating a complex phasor on the basis of said detected phases, and

(i) means for multiplying the baseband signal with said complex phasor for reducing the frequency offset of the baseband signal,

(j) means for producing a first channel estimation data,

(k) means for detecting phases from successive first channel estimation data,

(l) means for generating a complex phasor on the basis of said detected phases from successive first channel estimation data,

(m) means for multiplying the baseband signal with the complex phasor for correcting the frequency offset,

(n) means for producing a second channel estimation data on the basis of the frequency corrected signal, and

(o) means for multiplying an uncorrected baseband signal with the second channel estimate data for forming a corrected output signal.