Apparatus and method for hard handover in a wireless communication system

• US 20070135125A1
• Filed: 12/11/2006
• Published: 06/14/2007
• Est. Priority Date: 12/10/2005
• Status: Active Grant

• Current Assignee: Samsung Electronics Co. Ltd.
• Original Assignee: Samsung Electronics Co. Ltd.
• Inventors: Kim, Sung-Soo, Kim, Min-Goo, Gu, Young-Mo, Kim, Byung-Sik
• Granted Patent: US 7,860,502 B2
• Time in Patent Office: Days
• US Class Current: 455/436
• CPC Class Codes: H04B 1/7105 Joint detection techniques, e.g. linear detectors
• CPC Class Codes: H04B 2201/70702 Intercell-related aspects
• CPC Class Codes: H04W 36/0079 in case of hand-off failure or rejection
• CPC Class Codes: H04W 36/30 by measured or perceived connection quality data

Abstract

Provided is a hard handover method in a wireless communication system. The hard handover method includes checking a signal-to-noise ratio (SNR) of a signal received from each of at least one neighboring base station (BS) while in communication with a serving BS, and canceling interference if the SNR of the signal received from each of the at least one neighboring BSs satisfies a select condition; sending a handover request to the serving BS, if a difference between a SNR of the interference-canceled signal and a SNR of the interference signal reaches a handover request threshold; and upon receipt of a handover approval from the serving BS, releasing a communication channel to the serving BS, and connecting a call to a BS that provides an interference signal whose SNR has reached the threshold.

Claims

1. A hard handover method in a wireless communication system, comprising:

checking a signal-to-noise ratio (SNR) of a signal received from each of at least one neighboring base station (BS) while in communication with a serving BS, and canceling interference if the SNR of the signal received from each of the at least one neighboring BS satisfies a select condition;

sending a handover request to the serving BS, if a difference between a SNR of the interference-canceled signal and a SNR of the interference signal reaches a handover request threshold; and

upon receipt of a handover approval from the serving BS, releasing a communication channel to the serving BS, and connecting a call to a BS that provides an interference signal whose SNR has reached the threshold.

2. The hard handover method of claim 1, wherein the handover request includes a difference between a SNR of the interference-canceled signal and a SNR of the signal received from each of the at least one neighboring BS.

3. The hard handover method of claim 1, further comprising:

starting a timer being set to a select value, after sending the handover request; and

upon failure to receive a handover response signal from the serving BS, re-sending the handover request periodically at an interval substantially equal to the time set in the timer.

4. The hard handover method of claim 1, wherein the select condition comprises:

registering other BSs in an interferer candidate group (ICG), if a difference between a SNR of the signal received from the serving BS among all received interference signals and a SNR of the signal received from each of the other BSs is within a select threshold;

registering, in an interferer group (IG), any BS that transmit a signal having a higher strength than a threshold for interference cancellation among the signals in the ICG; and

canceling interference caused by the signal received from each of the BSs registered in the IG.

5. The hard handover method of claim 4, further comprising deregistering a corresponding BS from the IG and registering the corresponding BS in the ICG, if a SNR of the signal received from the corresponding BS registered in the IG is lower than a threshold of interference variance.

6. The hard handover method of claim 4, wherein if a SNR of a signal received from a BS registered in the IG decreases within a range of the threshold of interference variance, the BS remains in the IG and interference cancellation by the signal received from the BS is maintained.

7. The hard handover method of claim 4, wherein the threshold of interference variance is determined by simulating a variance in a Doppler frequency based on mean fading, and a variance in signal strength.

8. The hard handover method of claim 4, wherein the threshold of interference variance is determined by checking a variance in a Doppler frequency based on mean fading and a variance in signal strength in the field.

9. The hard handover method of claim 4, further comprising registering the serving BS in the ICG when the handover is completed.

10. The hard handover method of claim 4, further comprising deregistering a corresponding BS from the IG and registering the corresponding BS in the ICG, if strength of a signal from a BS in interference cancellation is less than the threshold for interference cancellation for a select amount of time.

11. The hard handover method of claim 1, further comprising:

completing the handover if a handover approval is not received until a strength of the signal received from the serving BS decreases lower than a threshold of serving cell detection; and

performing an initialization setting for searching for a new serving BS.

12. A hard handover method in a wireless communication system, comprising:

checking a signal-to-noise ratio (SNR) of a signal received from each of at least one neighboring base station (BS) while in communication with a serving BS, and canceling interference if the SNR of the signal received from each of the at least one neighboring BS satisfies a select condition;

estimating a transmitted symbol from a symbol demodulated during the interference cancellation, and calculating an energy difference between the demodulated symbol and the estimated symbol;

sending a handover request to the serving BS, if the energy difference reaches a handover request threshold; and

upon receipt of a handover approval from the serving BS, releasing a communication channel to the serving BS, and connecting a call to a BS that provides an interference signal whose SNR has reached the threshold.

13. The hard handover method of claim 12, wherein the handover request includes a difference between a SNR of the interference-canceled signal and a SNR of the signal received from each of the at least one BS.

14. The hard handover method of claim 12, further comprising:

starting a timer being set to a select value, after sending the handover request; and

upon failure to receive a handover response signal from the serving BS, re-sending the handover request periodically at an interval substantially equal to the time set in the timer.

15. The hard handover method of claim 12, wherein the select condition comprises:

registering other BSs in an interferer candidate group (ICG), if a difference between a SNR of the signal received from the serving BS among all received interference signals and a SNR of the signal received from each of the other BSs is within a select threshold;

registering, in an interferer group (IG), any BSs that transmit a signal having a higher strength than a threshold for interference cancellation among the signals in the ICG; and

canceling interference caused by the signal received from each of the BSs registered in the IG.

16. The hard handover method of claim 15, further comprising deregistering a corresponding BS from the IG and registering the corresponding BS in the ICG, if a SNR of the signal received from the corresponding BS registered in the IG is lower than a threshold of interference variance.

17. The hard handover method of claim 15, wherein if a SNR of a signal received from a BS registered in the IG decreases within a range of the threshold of interference variance, the BS remains in the IG and interference cancellation by the signal received from the BS is maintained.

18. The hard handover method of claim 15, wherein the threshold of interference variance is determined by simulating a variance in a Doppler frequency based on mean fading, and a variance in signal strength.

19. The hard handover method of claim 15, wherein the threshold of interference variance is determined by checking a variance in a Doppler frequency based on mean fading and a variance in signal strength in the field.

20. The hard handover method of claim 15, further comprising registering the serving BS in the ICG when the handover is completed.

21. The hard handover method of claim 15, further comprising deregistering a corresponding BS from the IG and registering the corresponding BS in the ICG, if strength of a signal from a BS in interference cancellation is less than the threshold for interference cancellation for a select amount of time.

22. The hard handover method of claim 12, further comprising:

completing the handover if a handover approval is not received until a strength of the signal received from the serving BS decreases lower than a threshold of serving cell detection; and

performing initialization setting for searching for a new serving BS.

23. A hard handover method in a wireless communication system, comprising:

checking a signal-to-noise ratio (SNR) of a signal received from each of at least one neighboring base station (BS) while in communication with a serving BS, and canceling interference if the SNR of the signal received from each of the at least one neighboring BS satisfies a select condition;

sending a handover request to the serving BS, if a SNR of the interference signal reaches a threshold for handover trial during the interference cancellation; and

upon receipt of a handover approval from the serving BS, releasing a communication channel to the serving BS, and connecting a call to a BS that provides an interference signal whose SNR has reached the threshold.

24. The hard handover method of claim 23, wherein the handover request includes a difference between a SNR of the interference-canceled signal and a SNR of the signal received from each of the at least one BS.

25. The hard handover method of claim 23, further comprising:

starting a timer being set to a specific value, after sending the handover request; and

upon failure to receive a handover response signal from the serving BS, re-sending the handover request periodically at an interval substantially equal to the time set in the timer.

26. The hard handover method of claim 23, wherein the select condition comprises:

registering other BSs in an interferer candidate group (ICG), if a difference between a SNR of the signal received from the serving BS among all received interference signals and a SNR of the signal received from each of the other BSs is within a select threshold;

registering, in an interferer group (IG), BSs that transmit a signal having higher strength than a threshold for interference cancellation among the signals in the ICG; and

canceling interference caused by the signal received from each of the BSs registered in the IG.

27. The hard handover method of claim 26, further comprising deregistering a corresponding BS from the IG and registering the corresponding BS in the ICG, if a SNR of the signal received from the corresponding BS registered in the IG is lower than a threshold of interference variance.

28. The hard handover method of claim 26, wherein if a SNR of a signal received from a BS registered in the IG decreases within a range of the threshold of interference variance, the BS remains in the IG and interference cancellation by the signal received from the BS is maintained.

29. The hard handover method of claim 26, wherein the threshold of interference variance is determined by simulating a variance in a Doppler frequency based on mean fading, and a variance in signal strength.

30. The hard handover method of claim 26, wherein the threshold of interference variance is determined by checking a variance in a Doppler frequency based on mean fading and a variance in signal strength in the field.

31. The hard handover method of claim 26, further comprising registering the serving BS in the ICG when the handover is completed.

32. The hard handover method of claim 26, further comprising deregistering a corresponding BS from the IG and registering the corresponding BS in the ICG, if a strength of a signal from a BS in interference cancellation is less than the threshold for interference cancellation for a select amount of time.

33. The hard handover method of claim 23, further comprising:

completing the handover if a handover approval is not received until a strength of the signal received from the serving BS decreases lower than a threshold of serving cell detection; and

performing initialization setting for searching for a new serving BS.

34. A hard handover apparatus in a wireless communication system, comprising:

a receiver for estimating a channel from each of at least one base station (BS), and converting a signal from a serving BS into data while receiving signals from BSs using the estimated information;

an interference signal generator for generating a signal of a particular interfering BS among the signals processed by the receiver, and generating an interference signal using the channel estimation information;

a transmitter for performing transmission of a signal and a control message to be transmitted to a BS; and

a controller for;

controlling the interference signal generator so as to cancel an interference signal, if a strength of a signal received from each of interfering BSs among the BSs satisfies an interference cancellation condition;

generating a handover request message and controlling transmission of the handover request message to the serving BS by controlling the controller, if strength of a signal received from a particular BS among the neighboring BSs satisfies a handover condition during the interference cancellation; and

upon receipt of a handover approval from the serving BS, controlling a release of a communication channel to the serving BS and controlling a connection of a call to the particular BS.

35. The hard handover apparatus of claim 34, wherein the handover condition is satisfied when a difference between a signal-to-noise ratio (SNR) of the interference-canceled signal and a SNR of the interference signal exceeds a select threshold.

36. The hard handover apparatus of claim 34, wherein a transmitted symbol is estimated from a symbol demodulated during the interference cancellation, and the handover condition is satisfied when an energy difference between the demodulated symbol and the estimated symbol exceeds a select threshold.

37. The hard handover apparatus of claim 34, wherein the handover condition is satisfied when a SNR of a signal received from each of neighbor BSs exceeds a select threshold.

38. The hard handover apparatus of claim 34, wherein the interference cancellation condition comprises:

registering other BSs in an interferer candidate group (ICG), if a difference between a SNR of the signal received from the serving BS among all received interference signals and a SNR of the signal received from each of the other BSs is within a select threshold;

registering, in an interferer group (IG), BSs that transmit a signal having higher strength than a threshold for interference cancellation among the signals in the ICG; and

canceling interference caused by the signal received from each of the BSs registered in the IG.

39. The hard handover apparatus of claim 38, wherein if a SNR of a signal received from a BS registered in the IG is lower than a threshold of interference variance, the BS is deregistered from the IG and registered in the ICG

40. The hard handover apparatus of claim 38, wherein if a SNR of the signal received from a BS registered in the IG decreases within a range of a threshold of interference variance, the BS remains in the IG and interference cancellation by the signal received from the BS is maintained.

41. The hard handover apparatus of claim 38, wherein the serving BS is registered in the ICG when the handover is completed.

42. The hard handover apparatus of claim 34, wherein the handover request message includes a difference between a SNR of the interference-canceled signal and a SNR of the interference signal transmitted from each of the BSs.

43. The hard handover apparatus of claim 34, wherein the handover request message comprises:

starting a timer being set to a specific value, after sending the handover request; and

upon failure to receive a handover response signal from the serving BS, re-sending the handover request periodically at an interval substantially equal to the time set in the timer.