Basestation for cellular communication system

• US 20080058017A1
• Filed: 05/08/2007
• Published: 03/06/2008
• 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
• Granted Patent: US 8,565,823 B2
• Time in Patent Office: Days
• 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 basestation within the network. As an alternative, the basestation may request information from one or 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:

detecting signals transmitted by at least one other basestation of the cellular communications system;

estimating a frequency error between a signal generated within said basestation and the detected signals transmitted by said at least one other basestation; and

controlling operation of said oscillator to minimize said error.

2. A method as claimed in claim 1, comprising estimating said frequency error based on CPICH signals transmitted by the least one other basestation.

3. A method as claimed in claim 1, comprising:

detecting signals transmitted by a plurality of other basestations of the cellular communications system;

forming estimates of a quality of each of said signals; and

estimating a combined frequency error based on estimated frequency errors between the signal generated within said basestation and the detected signals transmitted by the other basestations, wherein the estimation of the combined frequency error takes into account said quality estimates.

4. A method as claimed in claim 3, wherein the step of estimating the combined frequency error comprises forming a weighted sum of the estimated frequency errors between the signal generated within said basestation and the detected signals transmitted by the other basestations.

5. A method as claimed in claim 3, wherein the step of forming estimates of the quality of each of said signals comprises estimating the signal to noise ratios of said signals.

6. 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 time difference between frames transmitted from the basestation and another basestation;

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

7. A method as claimed in claim 6, wherein said first and second measurements of time differences are SFN-SFN measurements.

8. A method as claimed in claim 6, 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.