Cellular/WLAN hybrid-terminal handover techniques

• US 20070072609A1
• Filed: 09/26/2005
• Published: 03/29/2007
• Est. Priority Date: 09/26/2005
• Status: Active Grant

• Current Assignee: Google Technology Holdings LLC (Alphabet Inc.)
• Original Assignee: Motorola, Inc. (Motorola Solutions, Inc.)
• Inventors: Wu, Fei, Qiao, Yi
• Granted Patent: US 7,515,910 B2
• Time in Patent Office: Days
• US Class Current: 455/436
• CPC Class Codes: H04W 36/302 due to low signal strength

Abstract

Real-time handover decision techniques are provided which can utilize prior known system behavior in making a handover decision to avoid averaging delay and hysteresis delay.

Claims

1. In a wireless communication device, a method for deciding when to handover a communication device from a wireless communication network to a wireless local area network (WLAN) in real-time, the method comprising:

storing a first channel quality estimate of the WLAN prior to a first time instant;

measuring a sample of WLAN channel quality at the first time instant to generate a second channel quality measurement; and

generating a second channel quality estimate of the WLAN at the first time instant based on the second channel quality measurement and the first channel quality estimate.

2. In a wireless communication device, a communication device for deciding when to handover a communication device from a wireless communication network to a wireless local area network (WLAN) in real-time, the communication device comprising:

a memory configured to store a first channel quality estimate of the WLAN prior to a first time instant,

a measurement module configured to measure a sample of WLAN channel quality at the first time instant to generate a second channel quality measurement; and

a processor configured to generate a second channel quality estimate of the WLAN at the first time instant based on the second channel quality measurement and the first channel quality estimate.

3. In a wireless communication device, a method for deciding when to handover a communication device from a wireless communication network to a wireless local area network (WLAN) in real-time, the method comprising:

measuring samples of WLAN channel quality to generate a plurality of first channel quality measurements;

estimating channel quality of the WLAN for each sample based on the plurality of first channel quality measurements to generate a plurality of first channel quality estimates;

storing the first channel quality estimates prior to a first time instant;

measuring a second sample of WLAN channel quality at the first time instant to generate a second channel quality measurement;

defining a virtual window at the first time instant, wherein the virtual window comprises a number of samples (M), the second channel quality measurement CQM(i), and the plurality of first channel quality estimates;

determining the mean of the first channel quality estimates to within the virtual window at the first time instant; and

estimating channel quality of the WLAN at the first time instant based on the second channel quality measurement and the plurality of first channel quality estimates to generate a second channel quality estimate.

4. A method according to claim 3, further comprising:

determining the mean of the virtual window at the first time instant, wherein the mean of the virtual window comprises the mean of the second channel quality estimate and the plurality of the first channel quality estimates; and

determining a gradient of the mean of the virtual window at the first time instant.

5. A method according to claim 4, further comprising:

comparing the gradient of the mean to a gradient threshold;

identifying the WLAN as a candidate WLAN for handover if the gradient of the mean is greater than the gradient threshold;

comparing the mean to a first threshold; and

selecting the candidate WLAN as a selected WLAN suitable for handover if the mean is greater than the first threshold.

6. A method according to claim 5, further comprising:

determining a regression line for the channel quality measurement for the selected WLAN;

determining a mean square error of the regression line and a maximum mean square error of the regression line;

comparing the mean square error of the regression line to the maximum mean square error of the regression line; and

deciding to handover to the selected WLAN if the mean square error is less than the maximum mean square error.

7. A method according to claim 6, further comprising:

maintaining a connection to the wireless communication network if the mean square error for the regression line is greater than the maximum mean square error.

8. A method according to claim 7, further comprising:

determining whether the mean of the virtual window at the first time instant is less than a second threshold.

9. A method according to claim 8, wherein the mean square error is a first mean square error, wherein the maximum mean square error is a first maximum mean square error, and if the mean of the second channel quality measurement and the plurality of first channel quality estimates at the first time instant is greater than the second threshold, then:

determining a second regression line of the channel quality measurement for the selected WLAN;

determining a second mean square error of the second regression line and a second maximum mean square error of the second regression line;

comparing the second mean square error for the second regression line to the second maximum mean square error for the second regression line; and

deciding to handover to the selected WLAN if the second mean square error is less than the second maximum mean square error.

10. A method according to claim 8, further comprising:

maintaining a connection to the wireless communication network if the mean of the virtual window at the first time instant is less than the second threshold.

11. A communication device operable in a wireless communication network and a wireless local area network (WLAN) and adapted to make a handover decision in real-time, comprising:

a measurement module configured to measure samples of WLAN channel quality and generate a plurality of first channel quality measurements based on the samples;

a processor configured to estimate channel quality of the WLAN for each sample based on the plurality of first channel quality measurements and to generate a plurality of first channel quality estimates based on the first channel quality measurements;

a memory configured to store the first channel quality estimates prior to a first time instant,

wherein the measurement module is further configured to measure a second sample of WLAN channel quality at the first time instant to generate a second channel quality measurement based on the second sample, and

wherein the processor is configured to define a virtual window at the first time instant, wherein the virtual window comprises a number of samples (M), the second channel quality measurement CQM(i), and the plurality of first channel quality estimates, and

wherein the processor is configured to determine the mean of the first channel quality estimates to within the virtual window at the first time instant, and estimate channel quality of the WLAN at the first time instant based on the second channel quality measurement and the plurality of first channel quality estimates to generate a second channel quality estimate.

12. A communication device according to claim 11, wherein the processor is further configured to determine the mean of the virtual window at the first time instant, wherein the mean of the virtual window comprises the mean of the second channel quality estimate and the plurality of the first channel quality estimates, and wherein the processor is further configured to determine a gradient of the mean of the virtual window at the first time instant.

13. A communication device according to claim 12, wherein the processor is further configured to identify the WLAN as a candidate WLAN for handover if the gradient of the mean is greater than a gradient threshold.

14. A communication device according to claim 13, wherein the processor is further configured to select the candidate WLAN as a selected WLAN suitable for handover if the mean is greater than a first threshold.

15. A communication device according to claim 14, wherein the processor is further configured to determine a regression line of the channel quality measurement for the selected WLAN, determine a mean square error of the regression line and a maximum mean square error of the regression line, and decide to handover to the selected WLAN if the mean square error is less than the maximum mean square error.

16. A communication device according to claim 15, wherein the processor is further configured to maintain a connection to the wireless communication network if the mean square error for the regression line is greater than the maximum mean square error.

17. A communication device according to claim 16, wherein the processor is further configured to determine whether the mean of the virtual window at the first time instant is less than a second threshold.

18. A communication device according to claim 17, wherein the mean square error is a first mean square error, wherein the maximum mean square error is a first maximum mean square error, and

if the mean of the virtual window at the first time instant is greater than the second threshold, wherein the processor is further configured to determine a second regression line of the channel quality measurement for the selected WLAN, a second mean square error of the second regression line and a second maximum mean square error of the second regression line, and to decide to handover to the selected WLAN if the second mean square error is less than the second maximum mean square error.

19. A communication device according to claim 17, wherein the processor is further configured to maintain a connection to the wireless communication network if the mean of the virtual window at the first time instant is less than the second threshold.

20. A method in a wireless communication device, comprising:

defining a virtual window at a first time instance; and

using the virtual window to generate a channel quality estimate at the first time instance.

21. A method according to claim 20, further comprising:

determining a gradient of the virtual window; and

making a handover decision based on the channel quality estimate and the gradient of the virtual window.

22. A method according to claim 21, wherein using the virtual window to generate a channel quality estimate at the first time instance, comprises:

storing first channel quality estimates prior to the first time instance;

measuring channel quality at the first time instance to generate a first channel quality measurement, wherein the first channel quality estimates are based on channel quality measurements made prior to the first channel quality measurement; and

estimating channel quality at the first time instance using the virtual window defined at the first time instance to generate a second channel quality estimate at the first time instance.

23. A method according to claim 21, wherein the virtual window defined at the first time instance comprises the first channel quality estimates and the channel quality measurement, and wherein estimating channel quality at the first time instance using the virtual window defined at the first time instance to generate a second channel quality estimate at the first time instance, comprises:

estimating channel quality at the first time instance using the first channel quality estimates and the channel quality measurement to generate a second channel quality estimate at the first time instance.