Delay lock loops for wireless communication systems

• US 7,817,760 B2
• Filed: 03/03/2006
• Issued: 10/19/2010
• Est. Priority Date: 01/19/2001
• Status: Expired due to Fees

• Current Assignee: Qualcomm, Inc.
• Original Assignee: Qualcomm, Inc.
• Inventors: Black, Peter J., Sindhushayana, Nagabhushana T.
• Primary Examiner(s): Corrielus; Jean B
• Application Number:
  US11/368,115
• Publication Number:
  US 20060146918A1
• Time in Patent Office: 1,691 Days
• Field of Search: 375/130, 375/316, 375346-350, 375354-355, 375/224, 375/227, 455/296, 455/226.1, 455/226.2, 455/226.3, 370/500, 370/503
• US Class Current: 375/355
• CPC Class Codes: H03L 7/089 the phase or frequency detector generating up-down pulses H03L7/087 takes precedence
• CPC Class Codes: H03L 7/091 the phase or frequency detector using a sampling device H03L7/087 takes precedence
• CPC Class Codes: H03L 7/093 using special filtering or amplification characteristics in the loop H03L7/087 - H03L7/091 take precedence
• CPC Class Codes: H04B 7/082 selecting best antenna path

Abstract

Techniques for deriving sample timing for multiple signal instances received on multiple antennas for a given propagation path. In one scheme, a DLL is maintained for each path, and each DLL tracks the timing of the best signal instance for the assigned path. In another scheme, a DLL is maintained for each path, and each DLL tracks the average timing of the multiple signal instances for the assigned path. To reduce timing jitter, the SINR of a signal instance may be estimated for a number of different time offsets. The loop filter for the DLL is initially updated in the normal manner. If a change in the time offset used for the sample timing is detected, then the SINRs for the new and prior offsets are compared. The new time offset is used if the associated SINR is better. Otherwise, the prior time offset is retained and used.

Claims

1. A method for deriving sample timing for a plurality of signal instances received on a plurality of antennas at a receiver unit in a wireless communication system, comprising:

deriving an error metric from a signal energy for each of the plurality of signal instances received on a corresponding one of the plurality of antennas, the plurality of signal instances being different multi-path propagation instances of a transmitted first wireless signal, wherein each signal instance includes pilot samples, wherein deriving the error metric for each signal instance comprises subtracting energy of late pilot samples from energy of early pilot samples for each of the plurality of signal instances;

combining error metrics for the plurality of signal instances received on the plurality of antennas for each update period to provide a composite error metric for the update period, wherein each error metric is weighted based on a signal quality of each signal instance;

updating a loop filter based on the composite error metric;

deriving a first sample timing for the plurality of signal instances based on an output of the loop filter;

applying the same first sample timing to each of the plurality of signal instances, wherein the sample timing comprises one of the following;

a timing for the best signal instance from among the plurality of signal instances;

an average timing of the plurality of signal instances;

or

an average timing of a subset of the plurality of signal instances; and

combining the plurality of signal instances after applying the first sample timing to them to reconstruct a version of the first wireless signal.

2. The method of claim 1, wherein said combining step includes combining error metrics for signal instances having estimated signal qualities above a particular threshold.

3. The method of claim 1, wherein the signal quality of each signal instance includes a signal-to-noise-and-interference ratio (SINR).

4. The method of claim 1, wherein the error metric for each signal instance is derived with an early/late discriminator and based on data samples for the signal instance.

5. An apparatus adapted for deriving sample timing for a plurality of signal instances received on a plurality of antennas at a receiver unit in a wireless communication system, comprising:

means for deriving an error metric from a signal energy for each of the plurality of signal instances received on a corresponding one of the plurality of antenna, the plurality of signal instances being different multi-path propagation instances of a transmitted first wireless signal, wherein each signal instance includes pilot samples, wherein deriving the error metric for each signal instance comprises subtracting energy of late pilot samples from energy of early pilot samples for each of the plurality of signal instances;

means for combining error metrics, in a loop filter, for the plurality of signal instances received on the plurality of antennas for each update period to provide a composite error metric for the update period, wherein each error metric is weighted based on a signal quality of each signal instance, wherein the loop filter is updated based on the composite error metric;

means for deriving a first sample timing for the plurality of signal instances based on an output of the loop filter;

means for applying the same first sample timing to each of the plurality of signal instances, wherein the sample timing comprises one of;

a timing for the best signal instance from among the plurality of signal instances;

an average timing of the plurality of signal instances;

or

an average timing of a subset of the plurality of signal instances; and

means for combining the plurality of signal instances after applying the first sample timing to them to reconstruct a version of the first wireless signal.

6. The apparatus of claim 5, wherein said means for combining combines error metrics for signal instances having estimated signal qualities above a particular threshold.

7. The apparatus of claim 5, wherein the signal quality of each signal instance includes a signal-to-noise-and-interference ratio (SINR).

8. The apparatus of claim 5, wherein said means for deriving an error metric includes an early/late discriminator and said error metric is derived based on data samples for the signal instance.

9. An apparatus comprising:

a processor configured to

derive an error metric from a signal energy for each of the plurality of signal instances received on a corresponding one of the plurality of antennas, the plurality of signal instances being different multi-path propagation instances of a transmitted first wireless signal, wherein each signal instance includes pilot samples, wherein deriving the error metric for each signal instance comprises subtracting energy of late pilot samples from energy of early pilot samples for each of the plurality of signal instances;

combine error metrics for the plurality of signal instances received on the plurality of antennas for each update period to provide a composite error metric for the update period, wherein each error metric is weighted based on a signal quality of each signal instance;

update a loop filter based on the composite error metric, wherein the loop filter is implemented by the processor;

derive a first sample timing for the plurality of signal instances based on an output of the loop filter;

apply the same first sample timing to each of the plurality of signal instances, wherein the sample timing comprises one of;

a timing for the best signal instance from among the plurality of signal instances;

an average timing of the plurality of signal instances;

or

an average timing of a subset of the plurality of signal instances; and

combine the plurality of signal instances after applying the first sample timing to them to reconstruct a version of the first wireless signal.

10. A method for deriving sample timing for a plurality of signal instances received on a plurality of antennas at a receiver unit in a wireless communication system, comprising:

deriving an error metric from a signal energy for each of the plurality of signal instances received on a corresponding one of the plurality of antennas, the plurality of signal instances being different multi-path propagation instances of a transmitted first wireless signal, wherein each signal instance includes pilot samples, wherein deriving the error metric for each signal instance comprises subtracting energy of late pilot samples from energy of early pilot samples for each of the plurality of signal instances;

combining error metrics for the plurality of signal instances received on the plurality of antennas for each update period to provide a composite error metric for the update period, wherein each error metric is weighted based on a signal quality of each signal instance;

updating a loop filter based on the composite error metric;

deriving a first sample timing for the plurality of signal instances based on an output of the loop filter;

applying the same first sample timing to each of the plurality of signal instances, wherein the sample timing comprises a timing for the best signal instance from among the plurality of signal instances; and

combining the plurality of signal instances after applying the first sample timing to them to reconstruct a version of the first wireless signal.

11. A method for deriving sample timing for a plurality of signal instances received on a plurality of antennas at a receiver unit in a wireless communication system, comprising:

deriving an error metric from a signal energy for each of the plurality of signal instances received on a corresponding one of the plurality of antennas, the plurality of signal instances being different multi-path propagation instances of a transmitted first wireless signal, wherein each signal instance includes pilot samples, wherein deriving the error metric for each signal instance comprises subtracting energy of late pilot samples from energy of early pilot samples for each of the plurality of signal instances;

combining error metrics for the plurality of signal instances received on the plurality of antennas for each update period to provide a composite error metric for the update period, wherein each error metric is weighted based on a signal quality of each signal instance;

updating a loop filter based on the composite error metric;

deriving a first sample timing for the plurality of signal instances based on an output of the loop filter;

applying the same first sample timing to each of the plurality of signal instances, wherein the sample timing comprises an average timing of the plurality of signal instances; and

combining the plurality of signal instances after applying the first sample timing to them to reconstruct a version of the first wireless signal.

12. A method for deriving sample timing for a plurality of signal instances received on a plurality of antennas at a receiver unit in a wireless communication system, comprising:

deriving an error metric from a signal energy for each of the plurality of signal instances received on a corresponding one of the plurality of antennas, the plurality of signal instances being different multi-path propagation instances of a transmitted first wireless signal, wherein each signal instance includes pilot samples, wherein deriving the error metric for each signal instance comprises subtracting energy of late pilot samples from energy of early pilot samples for each of the plurality of signal instances;

combining error metrics for the plurality of signal instances received on the plurality of antennas for each update period to provide a composite error metric for the update period, wherein each error metric is weighted based on a signal quality of each signal instance;

updating a loop filter based on the composite error metric;

deriving a first sample timing for the plurality of signal instances based on an output of the loop filter;

applying the same first sample timing to each of the plurality of signal instances, wherein the sample timing comprises an average timing of a subset of the plurality of signal instances; and

combining the plurality of signal instances after applying the first sample timing to them to reconstruct a version of the first wireless signal.