Method and apparatus for combined timing recovery, frame synchronization and frequency offset correction in a receiver

• US 6,058,150 A
• Filed: 09/30/1997
• Issued: 05/02/2000
• Est. Priority Date: 09/30/1997
• Status: Expired due to Term

• Current Assignee: Quarterhill Inc. (f/k/a Wi-LAN Inc.)
• Original Assignee: Wireless Access Incorporated (EDCI Holdings Incorporated)
• Inventors: Ghosh, Biswa R.
• Primary Examiner(s): Chin, Stephen
• Assistant Examiner(s): JIANG, LENNY R
• Application Number:
  US08/941,598
• Time in Patent Office: 945 Days
• Field of Search: 375/365, 375/371, 375/344, 375/355, 375/334, 375/354, 375/362, 370/514
• US Class Current: 375/365
• CPC Class Codes: H04L 2027/0028 at passband only
• CPC Class Codes: H04L 2027/0055 single phase
• CPC Class Codes: H04L 7/042 Detectors therefor, e.g. correlators, state machines digital correlators in general G06F17/15
• CPC Class Codes: H04L 7/046 using a dotting sequence

Abstract

A method and apparatus for combined timing recovery, frame synchronization and frequency offset correction in a digital receiver is provided. In general, the present invention provides a pair of correlators that operate on a set of samples output by a discriminator. A positive correlator generates a positive correlation value and a negative correlator generates a negative correlation value. The positive and negative correlation values are used to determine frame synchronization, frequency offset and timing recovery values so that timing recovery, frame synchronization and frequency offset correction may be performed simultaneously.

Claims

1. A method for performing timing recovery, frame synchronization and frequency offset correction in a receiver comprising:

sampling a received analog signal;

determining an average amplitude of a predetermined number of most recent samples;

determining a first correlation value that indicates when a synchronization sequence is received based on the average amplitude;

performing a frequency offset correction based on a second correlation value which is based on the average amplitude, wherein the first correlation value and the second correlation value are determined simultaneously; and

sampling incoming data at a fixed offset from an end of the synchronization sequence.

2. The method of claim 1, wherein determining an average amplitude of a predetermined number of most recent samples further comprises:

summing the values of the predetermined number of most recent samples to generate an integrator output; and

multiplying the integrator output by a scale factor.

3. The method of claim 1, wherein determining an average amplitude of a predetermined number of most recent samples further comprises:

subtracting an oldest sample value of the predetermined number of most recent samples from the average amplitude of the predetermined number of most recent samples; and

adding a most recent sample value to the average amplitude of the predetermined number of most recent samples.

4. The method of claim 1, wherein determining a correlation value that indicates when a synchronization sequence is received further comprises:

determining a positive correlation value;

determining a negative correlation value;

subtracting the negative correlation value from the positive correlation value to determine the first correlation value; and

determining synchronization when the correlation value surpasses a predetermined threshold correlation value.

5. The method of claim 4, wherein the positive correlation value is determined by:

##EQU5## wherein i and k are indices over T/8-spaced samples.

6. The method of claim 4, wherein the negative correlation value is determined by:

##EQU6## wherein i and k are indices over T/8-spaced samples.

7. The method of claim 4, wherein the correlation value is determined by:

space="preserve" listing-type="equation">corr[k]=p.sub.-- corr[k]-n.sub.-- corr[k],

wherein k is an index value, p_-- corr[k] is the positive correlation value, and n_-- corr[k] is the negative correlation value.

8. The method of claim 1, wherein performing frequency offset correction further comprises:

determining a frequency offset value in proportion to the average amplitude of the predetermined number of most recent samples when the synchronization sequence is received; and

adjusting the sampling in response to the frequency offset value.

9. The method of claim 1, wherein performing frequency offset correction further comprises:

determining a frequency offset value in proportion to the average amplitude of the predetermined number of most recent samples when the synchronization sequence is received; and

correcting the received signal in response to the frequency offset value.

10. The method of claim 1 further comprising determining a timing phase, wherein the timing phase trails the sampling of an analog signal by a predetermined period of time.

11. An apparatus for performing timing recovery, frame synchronization and frequency offset correction in a digital receiver, wherein the receiver samples a signal at a predetermined rate, the apparatus comprising:

means for sampling a received analog signal;

means for determining an average amplitude of a predetermined number of most recent samples;

means for determining a correlation value that indicates when a synchronization sequence is received;

means for performing frequency offset correction based on inputs used to determine the correlation value; and

means for sampling incoming data at a fixed offset from an end of the synchronization sequence.

12. The apparatus of claim 11, wherein the means for determining an average amplitude of a predetermined number of most recent samples further comprises:

means for summing the values of the predetermined number of most recent samples to generate an integrator output; and

means for multiplying the integrator output by a scale factor.

13. The apparatus of claim 11, wherein the means determining an average amplitude of a predetermined number of most recent samples further comprises:

means for subtracting an oldest sample value of the predetermined number of most recent samples from the average amplitude of the predetermined number of most recent samples; and

means for adding a most recent sample value to the average amplitude of the predetermined number of most recent samples.

14. The apparatus of claim 11, wherein the means for determining a correlation value that indicates when a synchronization sequence is received further comprises:

means for determining a positive correlation value;

means for determining a negative correlation value;

means for subtracting the negative correlation value from the positive correlation value to determine the correlation value; and

means for determining synchronization when the correlation value surpasses a predetermined threshold correlation value.

15. The apparatus of claim 14, wherein the positive correlation value is determined by:

##EQU7## wherein i and k are indices over T/8-spaced samples.

16. The apparatus of claim 14, wherein the negative correlation value is determined by:

##EQU8## wherein i and k are indices over T/8-spaced samples.

17. The apparatus of claim 14, wherein the correlation value is determined by:

space="preserve" listing-type="equation">corr[k]=p.sub.-- corr[k]-n.sub.-- corr[k],

wherein k is an index value, p_-- corr[k] is a positive correlation value, and n_-- corr[k] is the negative correlation value.

18. The apparatus of claim 11, wherein the means for performing frequency offset correction further comprises:

means for determining a frequency offset value in proportion to the average amplitude of the predetermined number of most recent samples when the synchronization sequence is received;

means for adjusting the sampling in response to the frequency offset value.

19. The apparatus of claim 11, wherein the means for performing frequency offset correction further comprises:

means for determining a frequency offset value in proportion to the average amplitude of the predetermined number of most recent samples when the synchronization sequence is received;

means for correcting the received signal in response to the frequency offset value.

20. The apparatus of claim 11 further comprising means for determining a timing phase, wherein the timing phase trails the sampling of an analog signal by a predetermined period of time.

21. A circuit for performing timing recovery, frame synchronization and frequency offset correction in a digital receiver, the circuit comprising:

a discriminator to sample a signal and to output a digital signal;

an integrator to receive the digital signal and to generate an average amplitude of a predetermined number of most recent samples;

a positive correlator coupled to the integrator, the positive correlator to generate a positive correlation value;

a negative correlator coupled to the integrator, the negative correlator to generate a negative correlation value;

a first summing circuit coupled to the positive correlator and to the negative correlator, the first summing circuit to subtract the negative correlation value from the positive correlation value;

a threshold detector coupled to the first summing circuit, the th reshold detector to indicate frame synchronization when the output of the first summing circuit exceeds a predetermined value;

a second summing circuit coupled to the positive correlator and to the negative correlator, the second summing circuit to add the positive correlation value to the negative correlation value; and

an AFC circuit coupled to the second summing circuit, the AFC circuit to generate a frequency correction value in response to an output generated by the second summing circuit, wherein the frequency correction value is generated simultaneously with the frame synchronization, and further wherein a frequency offset value is generated simultaneously with the frequency correction value.

22. The circuit of claim 21, wherein the positive correlation value is determined by:

##EQU9## wherein i and k are indices over T/8-samples.

23. The circuit of claim 21, wherein the negative correlation value is determined by:

##EQU10## wherein i and k are indices over T/8-samples.