Basestation for cellular communication system

• US 8,041,393 B2
• Filed: 05/05/2010
• Issued: 10/18/2011
• Est. Priority Date: 08/29/2006
• Status: Active Grant

• Current Assignee: Cisco Technology, Inc. (Cisco Systems, Inc.)
• Original Assignee: Ubiquisys Limited (Cisco Systems, Inc.)
• Inventors: Whittaker, Stephen, Carter, Alan
• Primary Examiner(s): Gelin; Jean
• Assistant Examiner(s): Nguyen; Michael
• Application Number:
  US12/774,655
• Publication Number:
  US 20100216408A1
• Time in Patent Office: 531 Days
• Field of Search: 455/405, 455423-425, 455/435.2, 455439-444, 455 85- 87, 455/151.3, 455255-265, 455312-323, 455/561, 455/13.2, 455/24, 455/502, 455/125, 455/135, 370/379
• US Class Current: 455/561
• CPC Class Codes: H01Q 1/246 specially adapted for base stations
• CPC Class Codes: H03J 7/02 Automatic frequency control H03J7/18 takes precedence

Abstract

A basestation in a cellular communication system corrects frequency errors in signals generated within the basestation. The frequency errors may be corrected on the basis of signals transmitted by one or more other basestations within the network. As an alternative, the basestation may request information from one or more mobile devices that are also able to detect transmissions from other basestations.

Claims

1. A method for controlling operation of an oscillator in a basestation of a cellular communications system, the method comprising:

in said basestation, identifying at least one other basestation of the cellular communications system, and requesting a mobile device to report a first measurement of a time difference between frames transmitted from the basestation and the identified other basestation;

in said mobile device, making said first measurement, and reporting to said basestation;

in said basestation, requesting the mobile device to report a second measurement of the time difference between frames transmitted from the basestation and the identified other basestation;

in said mobile device, making said second measurement, and reporting to said basestation;

in said basestation, based on said reported first and second measurements, estimating a frequency offset between a signal generated within said basestation and a corresponding signal generated within said other basestation; and

applying a frequency control signal to said oscillator based on said estimated frequency offset.

2. A method as claimed in claim 1, wherein the step of estimating the frequency offset comprises:

determining a difference between the reported first and second measurements;

determining from said difference, an amount of difference that accumulates in a predetermined time period; and

estimating said frequency offset therefrom.

3. A method for controlling operation of an oscillator in a basestation of a cellular communications system, the method comprising:

requesting a mobile device to report a first measurement of a System Frame Number difference, representing a time difference between frames transmitted from the basestation and another basestation;

in said mobile device, making the first measurement of the System Frame Number difference, and reporting to said basestation;

requesting the mobile device to report a second measurement of the System Frame Number difference, representing the time difference between frames transmitted from the basestation and the other basestation;

in said mobile device, making the second measurement of the System Frame Number difference, and reporting to said basestation;

based on said reported first and second measurements, estimating a frequency offset between a signal generated within said basestation and a corresponding signal generated within said other basestation; and

controlling operation of said oscillator based on said estimated frequency offset.

4. A method for controlling operation of an oscillator in a basestation of a cellular communications system, the method comprising:

in said basestation, identifying a plurality of other basestations of the cellular communications system, and requesting a mobile device to report respective first measurements of a time difference between frames transmitted from the basestation and each identified other basestation;

in said mobile device, making said first measurements, and reporting to said basestation;

in said basestation, requesting the mobile device to report a second measurement of the time difference between frames transmitted from the basestation and the identified other basestations;

in said mobile device, making said second measurements, and reporting to said basestation;

in said basestation, based on said reported first and second measurements, estimating a frequency offset between a signal generated within said basestation and a corresponding signal generated within said other basestation; and

applying a frequency control signal to said oscillator based on said estimated frequency offset.

5. A method for controlling operation of an oscillator in a basestation of a cellular communications system, the method comprising:

identifying at least one other basestation of the cellular communications system;

requesting a mobile device to report a first measurement of a time difference between frames transmitted from the basestation and the identified other basestation;

receiving said first measurement from said mobile device;

requesting the mobile device to report a second measurement of the time difference between frames transmitted from the basestation and the identified other basestation;

receiving said second measurement from said mobile device;

based on said received first and second measurements, estimating a frequency offset between a signal generated within said basestation and a corresponding signal generated within said identified other basestation; and

applying a frequency control signal to said oscillator based on said estimated frequency offset.

6. A method as claimed in claim 5, wherein the step of estimating the frequency offset comprises:

determining a difference between the reported first and second measurements;

determining from said difference, an amount of difference that accumulates in a predetermined time period; and

estimating said frequency offset therefrom.

7. A method for controlling operation of an oscillator in a basestation of a cellular communications system, the method comprising:

requesting a mobile device to report a first measurement of a System Frame Number difference, representing a time difference between frames transmitted from the basestation and another basestation;

receiving from the mobile device the first measurement of the System Frame Number difference;

requesting the mobile device to report a second measurement of the System Frame Number difference, representing the time difference between frames transmitted from the basestation and the other basestation;

receiving from the mobile device the second measurement of the System Frame Number difference;

based on said received first and second measurements, estimating a frequency offset between a signal generated within said basestation and a corresponding signal generated within said other basestation; and

controlling operation of said oscillator based on said estimated frequency offset.

8. A method for controlling operation of an oscillator in a basestation of a cellular communications system, the method comprising:

in said basestation, identifying a plurality of other basestations of the cellular communications system, and requesting a mobile device to report respective first measurements of a time difference between frames transmitted from the basestation and each identified other basestation;

receiving from said mobile device said first measurements;

in said basestation, requesting the mobile device to report a second measurement of the time difference between frames transmitted from the basestation and the identified other basestations;

receiving from said mobile device said second measurements;

in said basestation, based on said received first and second measurements, estimating a frequency offset between a signal generated within said basestation and a corresponding signal generated within said other basestation; and

applying a frequency control signal to said oscillator based on said estimated frequency offset.

9. A method, comprising:

in a mobile device, receiving a request from a first basestation to report a first measurement representing a time difference between frames transmitted from the first basestation and a second basestation;

in said mobile device, making the first measurement, and reporting to said first basestation;

in said mobile device, receiving a request from the first basestation to report a second measurement representing the time difference between frames transmitted from the first basestation and the second basestation;

in said mobile device, making the second measurement, and reporting to said first basestation,

wherein based on said reported first and second measurements, the first basestation estimates a frequency offset between a signal generated within said first basestation and a corresponding signal generated within said second basestation, and

wherein the first basestation applies a frequency control signal to an oscillator in the basestation based on said estimated frequency offset.

10. A basestation in a cellular communications network configured to control operation of an oscillator in the basestation, the basestation comprising:

memory, and

one or more processors, the one or more processors configured to;

identify at least one other basestation of the cellular communications system, and request a mobile device to report a first measurement of a time difference between frames transmitted from the basestation and the identified other basestation;

receive from said mobile device said first measurement;

request the mobile device to report a second measurement of the time difference between frames transmitted from the basestation and the identified other basestation;

receive from said mobile device said second measurement;

based on said received first and second measurements, estimate a frequency offset between a signal generated within said basestation and a corresponding signal generated within said other basestation; and

apply a frequency control signal to said oscillator based on said estimated frequency offset.

11. A cellular wireless communications network, comprising:

one or more basestations, the one or more basestations configured to;

identify at least one other basestation of the cellular communications system, and request a mobile device to report a first measurement of a time difference between frames transmitted from the basestation and the identified other basestation;

receive from said mobile device said first measurement;

request the mobile device to report a second measurement of the time difference between frames transmitted from the basestation and the identified other basestation;

receive from said mobile device said second measurement;

based on said received first and second measurements, estimate a frequency offset between a signal generated within said basestation and a corresponding signal generated within said other basestation; and

apply a frequency control signal to said oscillator based on said estimated frequency offset; and

one or more mobile devices, the one or more mobile devices configured to;

make said first measurement, and report to said basestation;

make said second measurement, and report to said basestation.