Apparatus and method for synchronization in a multiple-carrier communications system by observing a phase-frequency relationship of a plurality of pilot signals

• US 6,940,933 B1
• Filed: 06/14/2000
• Issued: 09/06/2005
• Est. Priority Date: 06/23/1999
• Status: Expired due to Term

• Current Assignee: AT&T Mobility II LLC (AT&T, Inc.)
• Original Assignee: Cingular Wireless II LLC (AT&T, Inc.)
• Inventors: Heinonen, Jari M., Hirano, Michael R.
• Primary Examiner(s): Corrielus, Jean B.
• Assistant Examiner(s): Munoz, Guillermo
• Application Number:
  US09/593,547
• Time in Patent Office: 1,910 Days
• Field of Search: 370/503, 370/516, 370/517, 370/518, 370/519, 370/514, 370/515, 375/354, 375/355, 375/356, 375/373, 375/375, 375/362
• US Class Current: 375/354
• CPC Class Codes: H04L 27/261 Details of reference signals
• CPC Class Codes: H04L 27/2657 Carrier synchronisation
• CPC Class Codes: H04L 27/2662 Symbol synchronisation
• CPC Class Codes: H04L 27/2675 Pilot or known symbols

Abstract

A method, apparatus and system detects a loss of synchronization between a transmitter and a receiver in a multiple-carrier communication system such as an OFDM system. A phase-frequency synchronization detector determines when the receiver has lost synchronization with the transmitter based on a phase-frequency relationship of plurality of pilot signals transmitted at different frequencies from the transmitter and received at the receiver. A loss of synchronization is detected when a slope of a line defined by the phase-frequency relationship exceeds a timing threshold more at a rate in excess of an occurrence threshold within a time period.

Claims

1. A method for determining a loss of synchronization between a transmitter and a receiver:

receiving, at the receiver, a plurality of pilot signals having different frequencies from transmitter;

detecting a phase-frequency relationship of the plurality of pilot signals; and

determining loss of synchronization from the phase-frequency relationship;

wherein the phase-frequency relationship comprises a line defined by a relationship between a phase and a frequency of the plurality of pilot signals;

wherein determining comprises determining loss of synchronization based on a slope of the line; and

wherein determining further comprises determining loss of synchronization based on the number of times the slope exceeds a timing threshold.

2. A method in accordance with claim 1, wherein determining further comprises:

determining loss of synchronization when the number of times exceeds an occurrence threshold within a time period.

3. A method of determining a loss of synchronization between a transmitter and a receiver:

receiving, at the receiver, a plurality of pilot signals transmitted at different frequencies from the transmitter;

determining a slope of a line defined by a phase-frequency relationship of the plurality of pilot signals, the phase-frequency relationship defined by a plurality of phase-frequency values wherein each of a plurality of phase values is uniquely associated with each of a plurality of frequency values;

counting a number of times the slope exceeds a timing threshold; and

determining loss of synchronization between the transmitter and the receiver when the number of times is greater than an occurrence threshold in a time period.

4. A method in accordance with claim 3, wherein determining the slope comprises:

curve fitting the plurality of phase-frequency values using linear regression.

5. A method in accordance with claim 4, further comprising:

adjusting the receiver to synchronize the receiver to the transmitter in response to the loss of synchronization.

6. A phase-frequency slope synchronization detector comprising:

a phase detector adapted to determine a phase value for each of a plurality of received pilot signals transmitted from a transmitter at different frequencies; and

a controller adapted to determine a loss of synchronization between the transmitter and the receiver based on a phase-frequency relationship of the plurality of pilot signals;

wherein the phase-frequency relationship comprises a line defined by a relationship between a phase and a frequency of the plurality of pilot signals;

wherein the controller is further adapted to determine loss of synchronization based on a slope of the line; and

wherein the controller is further adapted to determine loss of synchronization based on the number of times the slope exceeds a timing threshold.

7. A phase-frequency slope synchronization detector in accordance with claim 6, wherein the controller is further adapted to determine loss of synchronization when the number of times exceeds an occurrence threshold within a time period.

8. A receiver for determining a loss of synchronization between the receiver and a transmitter comprising:

a demodulator adapted to demodulate a plurality of pilot signals transmitted at different frequencies from the transmitter; and

a phase-frequency synchronization detector adapted to;

determine a slope of a line defined by a phase-frequency relationship of the plurality of pilot signals, the phase-frequency relationship defined by a plurality of phase-frequency values wherein each of a plurality of phase values is uniquely associated with each of a plurality of frequency values;

count a number of times the slope exceeds a timing threshold; and

determine loss of synchronization between the transmitter and the receiver when the number of times is greater than an occurrence threshold in a time period.

9. A receiver in accordance with claim 8, wherein the phase-frequency synchronization detector is further adapted to determine the slope by applying a curve fitting algorithm using linear regression to the plurality of phase-frequency values.

10. A receiver in accordance with claim 9, wherein the controller is further adapted to adjust the demodulator to synchronize the receiver to the transmitter in response to the loss of synchronization.

11. A multiple-carrier wireless communication system comprising:

a transmitter adapted to transmit a plurality of pilot signals through a wireless communication channel, each of the pilot signals having a unique frequency; and

a receiver adapted to detect a loss of synchronization between the receiver and the transmitter based on a phase-frequency relationship of the pilot signals received at the receiver, the phase-frequency relationship comprising a line defined by a relationship between a phase and a frequency of the plurality of pilot signals;

wherein the receiver comprises the phase-frequency synchronization detector adapted to;

determine a slope of the line defined by a phase-frequency relationship of the plurality of pilot signals, the phase-frequency relationship defined by a plurality of phase-frequency values wherein each of a plurality of phase values is uniquely associated with each of a plurality of frequency values;

count a number of times the slope exceeds a timing threshold; and

determine loss of synchronization between the transmitter and the receiver when the number of times is greater than an occurrence threshold in a time period.