Delay compensation

• US 7,460,561 B2
• Filed: 07/19/2004
• Issued: 12/02/2008
• Est. Priority Date: 02/06/1997
• Status: Expired due to Fees

• Current Assignee: Clearwire Ip Holdings LLC (Deutsche Telekom AG)
• Original Assignee: Clearwire Corporation (Deutsche Telekom AG)
• Inventors: Hoole, Elliott
• Primary Examiner(s): Nguyen; Brian D
• Application Number:
  US10/894,257
• Publication Number:
  US 20040264549A1
• Time in Patent Office: 1,597 Days
• Field of Search: 370/519, 370/206, 370/210, 370/319, 370/252
• US Class Current: 370/519
• CPC Class Codes: H04B 1/69 Spread spectrum techniques
• CPC Class Codes: H04J 3/0682 by delay compensation, e.g. by compensation of propagation delay or variations thereof, by ranging
• CPC Class Codes: H04L 27/2646 using feedback from receiver for adjusting OFDM transmission parameters, e.g. transmission timing or guard interval length
• CPC Class Codes: H04L 27/2655 Synchronisation arrangements
• CPC Class Codes: H04L 27/2675 Pilot or known symbols
• CPC Class Codes: H04L 5/026 using code division

Abstract

In a discrete tone system, a base station receives a transmission burst from a remote unit being installed that includes delay compensation pilot tones that are uniformly spread throughout the transmission bandwidth. The arrival time transmission burst is not synchronized with the other remote units transmitting to the base station. The base station measures the phase delay of each tone and calculates the delay of the remote unit from the slope of the line of phase angle versus tone frequency. The base station transmits a signal to the remote unit that includes the magnitude and direction of the delay, which allows the remote unit to adapt the timing of its transmission to be synchronized with the other remote units.

Claims

1. A method for determining a delay compensation of signals transmitted between at least one remote unit and a base station of a wireless communication network, the method comprising:

receiving a first signal from the remote unit, the first signal comprising a plurality of delay compensation tones over a uniformly spaced frequency range;

calculating a phase shift difference between an expected phase and a received phase of the first signal for each of the tones;

unwrapping the phase shift difference associated with one or more of the tones;

linearly regressing the phase shift differences and the unwrapped phase shift differences; and

determining a slope of the linearly regressed phase shift differences, the slope being proportional to the delay compensation.

2. The method of claim 1, wherein the calculating is performed by a digital signal processor (DSP).

3. The method of claim 1, wherein calculating a phase shift difference includes calculating the phase shift difference from correlation coefficients relating to pairs of upper and lower sub-bands of tone bursts, the first signal including the tone bursts.

4. The method of claim 1, wherein calculating a phase shift difference includes calculating the phase shift difference from correlation coefficients relating to upper and lower sub-bands of the first signal received at one antenna element.

5. The method of claim 1, wherein calculating a phase shift difference includes calculating the phase shift difference from correlation coefficients relating to upper and lower sub-bands of the first signal received at more than one antenna element.

6. The method of claim 1, wherein the method is performed by a base station serving a geographic area of the wireless communication network.

7. An apparatus for providing signals within a wireless communication network, the apparatus comprising:

means for providing a first signal to the network, the first signal including delay compensation pilot (DCP) tones comprising frequencies that are spaced through an upper sub-band frequency range and a lower sub-band frequency range;

means for providing a second signal from the network, the second signal including time adjustment data that is determined from a phase difference between an expected phase angle and a received phase angle for each of the tones of the first signal, the phase differences being unwrapped, the unwrapped phase differences being fitted to a line, and a slope of the line being computed; and

means for providing a third signal to the network, wherein a time of transmission of the third signal is configured in accordance with the time adjustment data so that DCP tones of the third signal arrive at the network in phase with each other.

8. The apparatus of claim 7, wherein the slope of the line is proportional to the time adjustment data.

9. The apparatus of claim 7, wherein the time adjustment data is determined from the upper and lower sub-bands of the frequency range received at more than one antenna element included in the network.

10. The apparatus of claim 7, wherein the first signal is digitized into complex numbers representing a number of points in a Quadrature Amplitude Modulation (QAM) constellation, the complex numbers relating to an amount of energy of the DCP tones of the first signal in a frequency increment.

11. The apparatus of claim 7, wherein the first signal is transmitted before the second signal and the second signal is transmitted before the third signal.

12. An apparatus for adjusting a time of transmission of a signal from a mobile unit to a base station, the apparatus comprising:

means for receiving a first signal from the mobile unit, the first signal having a plurality of tones having upper-band and lower-band components over a spaced frequency range;

means for estimating a distance of the mobile unit from the base station to determine an estimated distance;

means for determining a delay measurement relating to phase differences within the tones of the first signal and the estimated distance;

means for transmitting the delay measurement to the mobile unit, the delay measurement configured to adjust a time of transmission of a second signal from the mobile unit to compensate for a delay existing in the first signal;

means for determining cutoff phase angles in accordance with the estimated distance, and wherein the means for determining a delay measurement includes means for normalizing phase differences to be within a range defined between the cutoff phase angles.

13. The apparatus of claim 12, wherein the means for determining a delay measurement includes means for fitting the phase differences to a line.

14. The apparatus of claim 12, further comprising:

means for digitizing the tones of the received first signal; and

means for transforming the digitized tones using a fast Fourier transform into complex numbers relating to an amount of energy of the received tones in a frequency increment.

15. The apparatus of claim 12, further comprising:

means for sampling and digitizing the tones of the first signals;

means for transforming the sampled and digitized tones through a fast Fourier transform processor to form Quadrature Amplitude Modulation (QAM) signals; and

means for storing the QAM signals in incremental frequency bins.

16. An apparatus for adjusting a time of transmission of a signal from a mobile unit to a base station, the apparatus comprising:

p1 means for receiving a first signal from the mobile unit, the first signal having a plurality of tones having upper-band and lower-band components over a spaced frequency range;

means for estimating a distance of the mobile unit from the base station to determine an estimated distance;

means for determining a positive cutoff phase angle and a negative cutoff phase angle in accordance with the estimated distance,

means for determining a delay measurement comprising;

means for detecting whether one or more pairs of adjacent phase differences within the tones of the first signal differ by more than the positive cutoff phase angle or less than the negative cutoff phase angle, each pair of the one or more pairs of adjacent phase differences having a first phase difference followed by a second phase difference,

means for adding −

2π

radians to the second phase difference of each pair of adjacent phase differences differing by more than the positive cutoff phase angle, and

means for adding 2π

radians to the second phase difference of each pair of adjacent phase differences differing by less than the negative cutoff phase angle; and

means for transmitting the delay measurement to the mobile unit, the delay measurement configured to adjust a time of transmission of a second signal from the mobile unit to compensate for a delay existing in the first signal.

17. The apparatus of claim 16, further comprising:

means for adding −

2π

radians to any phase differences following the second phase difference of each pair of adjacent phase differences within the tones of the first signal differing by more than the positive cutoff phase angle; and

means for adding 2π

radians to any phase differences following the second phase difference of each pair of adjacent phase differences within the tones of the first signal differing by less than the negative cutoff phase angle.

18. The apparatus of claim 16, wherein the means for determining a delay measurement includes means for fitting the phase differences to a line.