COMMUNICATION SIGNAL SYMBOL TIMING ERROR DETECTION AND RECOVERY

• US 20080240221A1
• Filed: 03/26/2008
• Published: 10/02/2008
• Est. Priority Date: 03/30/2007
• Status: Active Grant

• Current Assignee: DragonWave-X, LLC (COMSovereign Holding Corp.)
• Original Assignee: DragonWave Incorporated
• Inventors: MORRIS, Keith
• Granted Patent: US 8,036,332 B2
• Time in Patent Office: Days
• US Class Current: 375/232
• CPC Class Codes: H04L 2027/003 at baseband only
• CPC Class Codes: H04L 2027/0067 Phase error detectors
• CPC Class Codes: H04L 27/3863 Compensation for quadrature error in the received signal
• CPC Class Codes: H04L 7/0029 interpolation of received data signal
• CPC Class Codes: H04L 7/0278 Band edge detection

Abstract

Communication signal symbol timing error detection and recovery apparatus and techniques are disclosed. A communication signal that includes symbols is sampled according to receive symbol timing. The samples are band-edge filtered to provide a filtered output signal including band edges of the samples. The filtered output signal is converted to baseband, and a phase error of the receive symbol timing is calculated based on the down converted baseband signal. The communication signal may include symbols associated with quadrature channels, in which case a respective filtered output signal that includes band edges of samples associated with each quadrature channel may be down converted. The down converted baseband signals may then be separated into upper and lower band-edge signals, which are used to calculate a phase error of the receive symbol timing. The upper and lower band-edge signals may also be used for other purposes, such as slope equalization and/or carrier synchronization.

Claims

1. An apparatus comprising:

a band-edge filtering arrangement operable to receive as inputs samples of a received communication signal, and to provide a filtered output signal comprising band edges of the samples, the received communication signal comprising symbols and the samples comprising samples of the communication signal according to receive symbol timing;

a down converter operatively coupled to the band-edge filtering arrangement and operable to convert the filtered output signal to baseband; and

a symbol timing phase error calculator operatively coupled to the down converter and operable to calculate a phase error of the receive symbol timing based on the down converted baseband signal.

2. The apparatus of claim 1, wherein the down converter is operable to down convert the filtered output signal to baseband by multiplying the filtered output signal by quadrature carrier waveforms.

3. The apparatus of claim 2, wherein the quadrature carrier waveforms comprise four-cycle quadrature patterns.

4. The apparatus of claim 2, wherein the symbol timing phase error calculator comprises a sign function for determining a sign of a product of the filtered output signal and one of the quadrature carrier waveforms, and a multiplier for multiplying the product of the filtered output signal and another of the quadrature carrier waveforms by the determined sign.

5. The apparatus of claim 1, wherein the band-edge filtering arrangement comprises a low pass communication channel filter and a high pass filter operatively coupled to the low pass channel filter.

6. The apparatus of claim 1, further comprising:

a sample interpolator operatively coupled to the band-edge filtering arrangement and operable to provide the samples to the band-edge filtering arrangement; and

a feedback path operatively coupled between the symbol timing phase error calculator and the sample interpolator, the feedback path comprising a controller for adjusting the receive symbol timing based on the calculated symbol timing phase error.

7. The apparatus of claim 1, further comprising:

an Analog to Digital Converter (ADC) operatively coupled to the band-edge filtering arrangement and operable to provide the samples to the band-edge filtering arrangement;

a Voltage Controlled Oscillator (VCO) operatively coupled to the ADC and operable to generate the receive symbol timing; and

a feedback path operatively coupled between the symbol timing phase error calculator and the VCO, the feedback path comprising a controller for controlling the VCO to adjust the receive symbol timing based on the calculated symbol timing phase error.

8. The apparatus of claim 1, wherein the symbols comprise symbols associated with quadrature channels, wherein the filtered output signal comprises a respective filtered output signal comprising band edges of samples associated with each quadrature channel, and wherein the down converter is operable to convert the respective filtered output signals to baseband, the apparatus further comprising:

a band-edge signal separator operatively coupled to the down converter and operable to separate the down converted baseband signals into upper and lower band-edge signals; and

a symbol timing phase error calculator operatively coupled to the band-edge signal separator and operable to calculate a phase error of the receive symbol timing based on the upper and lower band-edge signals.

9. The apparatus of claim 8, wherein the down converter is operable to down convert the filtered output signals to baseband by multiplying each of the filtered output signals by quadrature carrier waveforms.

10. The apparatus of claim 8, wherein the band-edge signal separator comprises combiners operatively coupled to the down converter and operable to combine the down converted baseband signals into the upper and lower band-edge signals, and filters operatively coupled to the combiners and operable to filter non-baseband components out of the upper and lower band-edge signals.

11. The apparatus of claim 8, further comprising:

power calculators for calculating powers of the upper and lower band-edge signals; and

a combiner for calculating a difference between the powers of the upper and lower band-edge signals.

12. The apparatus of claim 8, further comprising:

a slope equalizer operatively coupled to the band-edge filtering arrangement; and

a feedback path operatively coupled between the band-edge signal separator and the slope equalizer, the feedback path comprising a controller for controlling the slope equalizer based on the upper and lower band-edge signals.

13. The apparatus of claim 12, further comprising:

a phase error feedback path operatively coupled to the symbol timing phase error calculator, the phase error feedback path comprising a controller for adjusting a phase of the receive symbol timing based on the calculated symbol timing phase error.

14. A method comprising:

band-edge filtering samples of a received communication signal to provide a filtered output signal comprising band edges of the samples, the received communication signal comprising symbols and the samples comprising samples of the communication signal according to receive symbol timing;

down converting the filtered output signal to baseband; and

calculating a phase error of the receive symbol timing based on the down converted baseband signal.

15. The method of claim 14, wherein down converting comprises multiplying the filtered output signal by quadrature carrier waveforms.

16. The method of claim 15, wherein the quadrature carrier waveforms comprise four-cycle quadrature patterns.

17. The method of claim 15, wherein calculating comprises determining a sign of a product of the filtered output signal and one of the quadrature carrier waveforms, and multiplying the product of the filtered output signal and another of the quadrature carrier waveforms by the determined sign.

18. The method of claim 14, further comprising:

interpolating samples of the received communication signal to provide the samples for band-edge filtering.

19. A computer-readable medium storing instructions which when executed perform the method of claim 14.

20. The method of claim 14, wherein the symbols comprise symbols associated with quadrature channels, wherein the filtered output signal comprises a respective filtered output signal comprising band edges of samples associated with each quadrature channel, and wherein the down converting comprises down converting the respective filtered output signals to baseband, the method further comprising:

separating the down converted baseband signals into upper and lower band-edge signals; and

calculating a phase error of the receive symbol timing based on the upper and lower band-edge signals.

21. The method of claim 20, wherein down converting comprises multiplying each of the filtered output signals by quadrature carrier waveforms.

22. The method of claim 20, wherein separating comprises combining the down converted baseband signals into the upper and lower band-edge signals, and filtering non-baseband components out of the upper and lower band-edge signals.

23. The method of claim 20, further comprising:

calculating power of the upper and lower band-edge signals; and

calculating a difference between the powers of the upper and lower band-edge signals.

24. The method of claim 20, further comprising:

adjusting a phase of the receive symbol timing based on the calculated symbol timing phase error.

25. A computer-readable medium storing instructions which when executed perform the method of claim 20.