Adaptive handover measurement interval

• US 20060205406A1
• Filed: 05/19/2005
• Published: 09/14/2006
• Est. Priority Date: 03/14/2005
• Status: Active Grant

• Current Assignee: WSOU Investments, LLC (WSOU Holdings, LLC)
• Original Assignee: Nokia Corporation
• Inventors: Vesma, Jussi, Pekonen, Harri J.
• Granted Patent: US 7,460,869 B2
• Time in Patent Office: Days
• US Class Current: 455/436
• CPC Class Codes: H04W 24/10 Scheduling measurement reports ; Arrangements for measurement reports
• CPC Class Codes: H04W 36/0088 Scheduling hand-off measurements
• CPC Class Codes: H04W 36/302 due to low signal strength
• CPC Class Codes: Y02D 30/70 in wireless communication networks

Abstract

Apparatus and methods are provided for adaptively determining a handover measurement interval. Power savings are achieved when a mobile terminal in a digital broadcast broadband network does not constantly attempt to measure the signal strength of nearby cells. By determining cell parameters, such as size and carrier frequency, and also determining dynamic information, such as signal strength and mobile speed over time, the time until the next handover measurement is adjusted up or down. When a mobile terminal is moving towards a transmitter in a cell, the handover measurement interval may be lengthened, and when a mobile terminal is moving away from a transmitter, the interval may be shortened.

Claims

1. A method for making a handover measurement, the method comprising steps of:

determining cell parameters for a current cell, wherein the current cell broadcasts a broadband digital signal;

determining a handover measurement interval based on the cell parameters;

measuring the signal quality of one or more candidate cells at a time varying based on the handover measurement interval.

2. The method of claim 1, further comprising:

receiving the broadband digital signal from the current cell;

determining a rate of signal quality change over time for the current cell; and

determining the handover measurement interval further based on the rate of signal quality change.

3. The method of claim 2, wherein the rate of signal quality change over time is determined at least in part by calculating a rate of signal strength change.

4. The method of claim 2, wherein the rate of signal quality change over time is determined at least in part by calculating a rate of change for one of a bit error ratio and a packet error ratio.

5. The method of claim 1, further comprising:

determining a receiver speed relative to a cell transmission station; and

determining the handover measurement interval further based on the receiver speed.

6. The method of claim 5, wherein the receiver speed relative to a cell transmission station is determined in part by measuring the Doppler shift of signals received from the cell transmission station.

7. The method of claim 1, wherein cell parameters comprise a size of the current cell.

8. The method of claim 1, further comprising:

adjusting the handover measurement interval so that a handover measurement is scheduled to coincide with receiving a signal broadcast from the current cell.

9. A mobile terminal, comprising:

a receiver, capable of receiving a digital broadband broadcast signal from a transmitter in a current cell;

a processor, configured to perform the steps of;

determining parameters for the current cell;

determining a handover measurement interval based on the current cell parameters; and

scheduling a handover measurement at a time based on the handover measurement interval.

10. The mobile terminal of claim 9, further comprising:

a memory, and

wherein the processor is further configured to perform steps of;

storing signal quality information for the current cell in the memory; and

calculating an adjustment to the handover measurement interval based on the stored signal quality information for the current cell.

11. The mobile terminal of claim 10, wherein the signal quality information comprises signal strength measurements over time.

12. The mobile terminal of claim 10, wherein the signal quality information comprises one of a bit error ratio and a packet error ratio calculated over time.

13. The mobile terminal of claim 9, wherein the processor is further configured to perform steps of:

determining a speed of the mobile terminal relative to the transmitter;

calculating an adjustment to the handover measurement interval based on the mobile terminal speed.

14. The mobile terminal of claim 13, wherein the speed of the mobile terminal is determined by estimating the Doppler shift of a carrier frequency caused by movement of the mobile terminal.

15. The mobile terminal of claim 9, wherein current cell parameters are determined by receiving the parameters via the digital broadband broadcast signal.

16. The mobile terminal of claim 15, wherein current cell parameters comprise a cell size.

17. The mobile terminal of claim 9, wherein the processor is further configured to perform the step of:

adjusting the handover measurement interval so that the handover measurement is timed to coincide with a scheduled reception of the digital broadband broadcast signal.

18. A mobile terminal, comprising:

a receiver, capable of receiving digital broadband broadcast burst signals from a transmitter in a cell;

a memory, capable of storing information relevant to the cell;

a processor, configured to;

determine a size of the cell;

retrieve signal quality measurements from the receiver;

store signal quality measurements in the memory;

determine a handover measurement interval based on the size of the cell;

adjust the handover measurement interval based on the signal quality measurements stored in the memory; and

schedule handover measurements at a time based on the handover measurement interval.

19. The mobile terminal of claim 18, wherein the processor is configured to determine the size of the current cell by:

receiving longitude and latitude information about the cell via the receiver from the digital broadband broadcast burst signals; and

calculating a size of the cell based on the longitude and latitude information.

20. The mobile terminal of claim 18, further comprising:

a positioning system, wherein the processor is further configured to;

receive a location of the mobile terminal from the positioning system;

calculate a speed and a direction of the mobile terminal based on changes in the location; and

adjust the handover measurement interval based on the calculated speed and direction of the mobile terminal.

21. A set of one or more integrated circuits, the set comprising:

circuitry configured to perform steps of;

determining a rate at which signal quality is changing; and

determining at least a portion of a handover measurement interval based on the rate at which signal quality is changing.

22. An integrated circuit, comprising:

circuitry configured to perform steps of;

determining a speed of a mobile device moving through a current cell; and

determining at least a portion of a handover measurement interval based on the speed of the mobile device.

23. The integrated circuit of claim 22, wherein determining a speed of a mobile device moving through a current cell comprises:

receiving a channel impulse response of a Doppler shifted signal;

performing a Fast Fourier Transform on the channel impulse response to produce a Doppler power spectrum;

estimating a Doppler spread frequency based on the Doppler power spectrum; and

calculating the speed of the mobile device by dividing the Doppler spread frequency by a carrier frequency and multiplying the resulting ratio by the speed of light.

24. At least one integrated circuit, comprising:

circuitry configured to perform steps of;

determining that signal quality of a current cell is declining; and

creating a list of candidate signals, wherein a sliding average of signal strength is computed and stored with the list for at least one candidate signal.