Frequency locked feedback loop for wireless communications

• US 8,140,034 B2
• Filed: 11/24/2009
• Issued: 03/20/2012
• Est. Priority Date: 11/24/2009
• Status: Active Grant

• Current Assignee: MediaTek, Inc.
• Original Assignee: International Business Machines Corporation
• Inventors: DeCusatis, Casimer M., Jacobowitz, Lawrence
• Primary Examiner(s): Phu, Sanh
• Application Number:
  US12/624,677
• Publication Number:
  US 20110122983A1
• Time in Patent Office: 847 Days
• Field of Search: 455/126, 455/315, 455/59, 455/266, 455/255, 455/205, 375/376, 375/259
• US Class Current: 455/126
• CPC Class Codes: H03C 3/09 Modifications of modulator for regulating the mean frequency

Abstract

A method and systems for a frequency locked feedback loop for wireless communications are provided. The method includes applying dither modulation from a harmonic modulator to modulated data at a transmit source, and mixing the dither modulation at a dither modulation frequency with the modulated data at a wireless carrier frequency to produce a modulated signal. The method also includes filtering and splitting the modulated signal using a bandpass filter to produce a wireless output signal and a feedback signal. The method further includes determining a frequency error in the feedback signal as a function of alignment of the wireless carrier frequency to a target frequency in a frequency response of the bandpass filter. The method additionally includes adjusting the wireless carrier frequency in response to the frequency error to establish a frequency lock between the wireless carrier frequency and the target frequency.

Claims

1. A method for providing a frequency locked feedback loop for wireless communications, comprising:

applying dither modulation from a harmonic modulator to modulated data at a transmit source;

mixing the dither modulation at a dither modulation frequency with the modulated data at a wireless carrier frequency to produce a modulated signal;

filtering and splitting the modulated signal using a bandpass filter to produce a wireless output signal and a feedback signal;

determining a frequency error in the feedback signal as a function of alignment of the wireless carrier frequency to a target frequency in a frequency response of the bandpass filter; and

adjusting the wireless carrier frequency in response to the frequency error to establish a frequency lock between the wireless carrier frequency and the target frequency.

2. The method of claim 1 wherein the frequency error is determined as a function of a vector cross product of the dither modulation and the feedback signal, the vector cross product producing a vector cross product signal.

3. The method of claim 2 further comprising:

filtering the vector cross product signal using a lowpass filter to generate a filtered vector cross product;

integrating and digitizing the filtered vector cross product over a period of time to produce an averaged frequency error; and

applying the averaged frequency error to a signal bias block as the error signal, wherein the signal bias block adjusts the wireless carrier frequency.

4. The method of claim 3 wherein the amplitude of the averaged frequency error is proportional to an offset between the wireless carrier frequency and the target frequency, and a phase offset of the averaged frequency error is positive or negative as function of the wireless carrier frequency being higher or lower than the target frequency.

5. The method of claim 3 further comprising:

shifting an output of the signal bias block in response to values in a calibration table.

6. The method of claim 1 wherein the target frequency in the frequency response of the bandpass filter is selectable as an arbitrary point, and the frequency error is tracked as a nonequilibrium frequency error to adjust the wireless carrier frequency.

7. The method of claim 6 wherein the frequency response of the bandpass filter is a comb filter comprising a plurality of frequency peaks, and the arbitrary point is selectable as a null between at least two of the plurality of frequency peaks.

8. The method of claim 7 further comprising:

providing variable frequency resolution by varying one or more of an amplitude and frequency of the modulated signal to span across two or more of the plurality of frequency peaks;

monitoring the frequency error to determine a number of frequency peaks and nulls passed and a direction passed according to a relative frequency and phase of the frequency error to reach the arbitrary point;

stepping the wireless carrier frequency to the arbitrary point within a tolerance band based on the number of frequency peaks and nulls passed and the direction passed; and

reducing the varied one or more of the amplitude and frequency to narrow frequency resolution of the frequency error and increase frequency lock precision.

9. The method of claim 1 further comprising:

receiving the target frequency and the modulated data from a multicore device, wherein the multicore device periodically modifies the target frequency providing frequency tunable security for communications over a wireless network.

10. A system for a frequency locked feedback loop for wireless communications, comprising:

a harmonic modulator to produce a dither modulation at a dither modulation frequency;

a transmit source configured to mix the dither modulation at the dither modulation frequency with modulated data at a wireless carrier frequency to produce a modulated signal;

a bandpass filter and splitter in communication with the transmit source and configured to output a wireless output signal and a feedback signal from the modulated signal; and

a frequency adjustment function configured to determine frequency error in the feedback signal as a function of alignment of the wireless carrier frequency to a target frequency in a frequency response of the bandpass filter and command adjustment of the wireless carrier frequency in response to the frequency error to establish a frequency lock between the wireless carrier frequency and the target frequency.

11. The system of claim 10 wherein the frequency adjustment function further comprises:

a vector cross product function configured to produce a vector cross product signal as a vector cross product of the dither modulation and the feedback signal.

12. The system of claim 11 further comprising a signal bias block between the harmonic modulator and the transmit source, wherein frequency adjustment function further comprises:

a lowpass filter to filter the vector cross product signal and generate a filtered vector cross product; and

an integrate and digitize function to produce an averaged frequency error by integrating and digitizing the filtered vector cross product over a period of time, wherein the averaged frequency error provides an adjustment command to the signal bias block to adjust the wireless carrier frequency.

13. The system of claim 12 wherein the amplitude of the averaged frequency error is proportional to an offset between the wireless carrier frequency and the target frequency, and a phase offset of the averaged frequency error is positive or negative as function of the wireless carrier frequency being higher or lower than the target frequency.

14. The system of claim 12 further comprising:

a shifter and a calibration table, wherein the shifter is configured to shift output of the signal bias block in response to values in the calibration table.

15. The system of claim 10 wherein the target frequency in the frequency response of the bandpass filter is selectable as an arbitrary point, and the frequency error is tracked as a nonequilibrium frequency error to adjust the wireless carrier frequency.

16. The system of claim 15 wherein the frequency response of the bandpass filter is a comb filter comprising a plurality of frequency peaks, and the arbitrary point is selectable as a null between at least two of the plurality of frequency peaks.

17. The system of claim 10 wherein the frequency adjustment function is implemented in digital signal processing circuitry.

18. The system of claim 10 further comprising:

a multicore device to provide the target frequency and the modulated data, wherein the multicore device is configured to periodically modify the target frequency as part of frequency tunable security for communications over a wireless network.

19. A wireless communication security system, comprising:

a multicore device in communication with a plurality of frequency locked feedback loops, wherein the plurality of frequency locked feedback loops are independently configurable to lock on separate target frequencies and output modulated data on wireless carrier frequencies aligned with the separate target frequencies, and the multicore device is configured to periodically modify the separate target frequencies to provide frequency tunable security for communications over a wireless network.

20. The wireless communication security system of claim 19 wherein each of the frequency locked feedback loops receives a selected target frequency from the multicore device, and each of the frequency locked feedback loops further comprises:

a transmit source configured to mix the dither modulation at the dither modulation frequency with modulated data at a wireless carrier frequency to produce a modulated signal;

a bandpass filter and splitter in communication with the transmit source and configured to output a wireless output signal and a feedback signal from the modulated signal; and

a frequency adjustment function configured to determine frequency error in the feedback signal as a function of alignment of the wireless carrier frequency to the selected target frequency in a frequency response of the bandpass filter and command adjustment of the wireless carrier frequency in response to the frequency error to establish a frequency lock between the wireless carrier frequency and the selected target frequency.