Delay compensation

• US 6,785,300 B2
• Filed: 10/17/2002
• Issued: 08/31/2004
• Est. Priority Date: 02/06/1997
• Status: Expired due to Fees

• Current Assignee: Clearwire Ip Holdings LLC (Deutsche Telekom AG)
• Original Assignee: AT&T Wireless Services Incorporated (AT&T, Inc.)
• Inventors: Hoole, Elliott
• Primary Examiner(s): NGUYEN, BRIAN D
• Application Number:
  US10/272,272
• Publication Number:
  US 20030053488A1
• Time in Patent Office: 684 Days
• Field of Search: 370/503, 370/506, 370/508, 370/516, 370/518, 370/519, 370/480, 370/481, 370/483, 370/484, 370/328, 370/334, 370/319, 370/339, 370/344, 370/206, 370/207, 370/210, 370/252, 370/320, 370/335, 370/342, 375/130, 375/261, 375/268, 375/269
• 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. An apparatus for determining a delay compensation of signals transmitted between at least one remote unit and a base station of a wireless communication network, the apparatus comprising:

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

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

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

means for linearly regressing the phase shift difference and the unwrapped phase shift differences; and

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

2. The apparatus of claim 1, wherein the means for calculating comprises a digital signal processor (DSP).

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

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

5. The apparatus of claim 1, wherein means for calculating a phase shift difference includes means for 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 apparatus of claim 1, wherein the apparatus is a base station serving a geographic area of the wireless communication network.

7. A method for providing signals within wireless communication network, the comprising:

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

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

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 method of claim 7, wherein the slope of the line is proportional to the time adjustment data.

9. The method 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 method 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 DCP tones in a frequency increment.

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

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

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 uniformly spaced frequency range;

estimating a distance of the mobile unit from the base station;

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

transmitting the delay measurements 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; and

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

13. A system for providing time delay compensation between first and second stations in a wireless network, comprising:

means for receiving at the first station a plurality of discrete, delay compensation tones with frequencies that are uniformly spaced throughout a frequency range;

means for measuring a phase difference between an expected phase angle and a received a phase angle for each compensation tone;

means for calculating a rate of change of phase differences as a function of frequency for the compensation tones;

means for determining a time delay compensation from the rate of change and the uniform frequency spacing; and

means for sending a signal indicating the time delay compensation to the second station.

14. A system for providing time delay compensation between first and second stations in a wireless network, comprising:

means for receiving at the first station a plurality of discrete, delay compensation tones with frequencies that are uniformly spaced throughout a frequency range;

means for measuring a phase difference between an expected phase angle and a received phase angle for each compensation tone;

means for calculating a rate of change of phase difference as a function of frequency for the compensation tones;

means for determining a time delay compensation from the rate of change and the uniform frequency spacing;

means for sending a signal indicating the time delay compensation to the second station; and

means for adjusting timing at the second station using the time delay compensation signal.