Apparatus and method for hard handover in a wireless communication system

• US 7,860,502 B2
• Filed: 12/11/2006
• Issued: 12/28/2010
• Est. Priority Date: 12/10/2005
• Status: Active Grant

• Current Assignee: Samsung Electronics Co. Ltd.
• Original Assignee: Samsung Electronics Co. Ltd.
• Inventors: Kim, Byung-Sik, Kim, Sung-Soo, Kim, Min-Goo, Gu, Young-Mo
• Primary Examiner(s): Phan; Huy
• Assistant Examiner(s): WANG-HURST, KATHY W
• Application Number:
  US11/636,456
• Publication Number:
  US 20070135125A1
• Time in Patent Office: 1,478 Days
• Field of Search: 370331-334, 370/310, 4554321-444, 455436-453
• 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 performed by a mobile terminal in a wireless communication system including a serving base station (BS) currently serving the mobile terminal and at least one neighboring BS, the mobile terminal located within both a border of a cell served by the serving BS and a border of a cell served by the at least one neighboring BS, the method comprising:

checking, by the mobile terminal, a signal-to-noise ratio (SNR) of an interference signal received from the at least one neighboring BS while in communication with the serving BS, and canceling, by the mobile terminal, from a signal received from the serving BS, interference caused by the interference signal received from the at least one neighboring BS, to generate an interference-canceled signal if, upon using an operation, it is determined that the SNR of the interference signal received from the at least one neighboring BS satisfies a select condition;

sending, by the mobile terminal, a handover request to the serving BS, if a difference between an SNR of the interference-canceled signal and the SNR of the interference signal received from the at least one neighboring BS reaches a handover request threshold; and

upon receipt of a handover approval from the serving BS, releasing, by the mobile terminal, a communication channel to the serving BS, and connecting, by the mobile terminal, a call to the at least one neighboring BS that provides the interference signal whose SNR has satisfied the select condition;

wherein the operation used for determining whether the SNR of the interference signal received from the at least one neighboring BS satisfies the select condition comprises;

registering, in an interferer candidate group (ICG), any neighboring BS if a difference between an SNR of the signal received from the serving BS and an SNR of a signal received from the neighboring BS is within a select threshold;

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

canceling interference caused by a signal received from each of BS(s) registered in the IG.

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

3. The hard handover method of claim 1, further comprising deregistering a corresponding BS from the IG and registering the corresponding BS in the ICG, if an SNR of a signal received from the corresponding BS registered in the IG is lower than a threshold of interference variance.

4. The hard handover method of claim 1, wherein if an SNR of a signal received from a BS registered in the IG decreases within a range of a threshold of interference variance, the BS registered in the IG remains in the IG and interference cancellation by the signal received from the BS registered in the IG is maintained.

5. The hard handover method of claim 1, wherein a threshold of interference variance is determined by simulating a variance in a Doppler frequency based on mean fading, and a variance in a signal strength.

6. The hard handover method of claim 1, further comprising registering the serving BS in the ICG when the handover is completed.

7. 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.

8. A hard handover method performed by a mobile terminal in a wireless communication system including a serving base station (BS) currently serving the mobile terminal and at least one neighboring BS, the mobile terminal located within both a border of a cell served by the serving BS and a border of a cell served by the at least one neighboring BS, the method comprising:

checking, by the mobile terminal, a signal-to-noise ratio (SNR) of an interference signal received from the at least one neighboring BS while in communication with the serving BS, and canceling, by the mobile terminal, from a signal received from the serving BS, interference caused by the interference signal received from the at least one neighboring BS to generate an interference-canceled signal if, upon using an operation, it is determined that the SNR of the interference signal received from the at least one neighboring BS satisfies a select condition;

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

sending, by the mobile terminal, 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, by the mobile terminal, a communication channel to the serving BS, and connecting, by the mobile terminal, a call to the at least one neighboring BS that provides the interference signal whose SNR has satisfied the select condition;

wherein the operation used for determining whether the SNR of the interference signal received from the at least one neighboring BS satisfies the select condition comprises;

registering, in an interferer candidate group (ICG), any neighboring BS if a difference between an SNR of the signal received from the serving BS and an SNR of a signal received from the neighboring BS is within a select threshold;

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

canceling interference caused by a signal received from each of BS(s) registered in the IG.

9. The hard handover method of claim 8, wherein the handover request includes a difference between an SNR of the interference-canceled signal and the SNR of the interference signal received from each of the at least one neighboring BS.

10. The hard handover method of claim 8, further comprising deregistering a corresponding BS from the IG and registering the corresponding BS in the ICG, if an SNR of a signal received from the corresponding BS registered in the IG is lower than a threshold of interference variance.

11. The hard handover method of claim 8, wherein if an SNR of a signal received from a BS registered in the IG decreases within a range of a threshold of interference variance, the BS registered in the IG remains in the IG and interference cancellation by the signal received from the BS registered in the IG is maintained.

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

13. The hard handover method of claim 8, further comprising registering the serving BS in the ICG when the handover is completed.

14. The hard handover method of claim 8, 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.

15. A hard handover method performed by a mobile terminal in a wireless communication system including a serving base station (BS) currently serving the mobile terminal and at least one neighboring BS, the mobile terminal located within both a border of a cell served by the serving BS and a border of a cell served by the at least one neighboring BS, the method comprising:

checking, by the mobile terminal, a signal-to-noise ratio (SNR) of an interference signal received from the at least one neighboring BS while in communication with the serving BS, and canceling, by the mobile terminal, from a signal received from the serving BS, interference caused by the interference signal received from the at least one neighboring BS to generate an interference-canceled signal if, upon using an operation, it is determined that the SNR of the interference signal received from the at least one neighboring BS satisfies a select condition;

sending, by the mobile terminal, a handover request to the serving BS, if an SNR of the interference signal received from the at least one neighboring BS reaches a threshold for handover trial during an interference cancellation; and

upon receipt of a handover approval from the serving BS, releasing, by the mobile terminal, a communication channel to the serving BS, and connecting, by the mobile terminal, a call to the at least one neighboring BS that provides the interference signal whose SNR has satisfied the select condition;

wherein the operation used for determining whether the SNR of the interference signal received from the least one neighboring BS satisfies the select condition comprises;

registering, in an interferer candidate group (ICG), any neighboring BS if a difference between an SNR of the signal received from the serving BS and an SNR of a signal received from the neighboring BS is within a select threshold;

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

canceling interference caused by a signal received from each of BS(s) registered in the IG.

16. The hard handover method of claim 15, wherein the handover request includes a difference between an SNR of the interference-canceled signal and the SNR of the interference signal received from each of the at least one neighboring BS.

17. 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 an SNR of a signal received from the corresponding BS registered in the IG is lower than a threshold of interference variance.

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

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

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:

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.

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

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

an interference signal generator for generating a signal of a particular interfering BS among 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, upon using an operation, it is determined that 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 transmitter, if a 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;

wherein the operation used for determining whether a strength of a signal received from each of interfering BSs among the BSs satisfies the interference cancellation condition comprises;

registering, in an interferer candidate group (ICG), any neighboring BS if a difference between an SNR of the signal received from the serving BS and an SNR of a signal received from the neighboring BS is within a select threshold;

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

canceling interference caused by a signal received from each of BS(s) registered in the IG.

23. The hard handover apparatus of claim 22, wherein the handover condition is satisfied when a difference between an SNR of a interference-canceled signal and an SNR of the interference signal exceeds a select threshold.

24. The hard handover apparatus of claim 22, 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.

25. The hard handover apparatus of claim 22, wherein the handover condition is satisfied when an SNR of a signal received from each of neighbor BSs exceeds a select threshold.

26. The hard handover apparatus of claim 22, wherein if an SNR of a signal received from a BS registered in the IG decreases within a range of a threshold of interference variance, the BS registered in the IG remains in the IG and interference cancellation by the signal received from the BS registered in the IG is maintained.

27. The hard handover apparatus of claim 22, wherein the serving BS is registered in the ICG when the handover is completed.

28. The hard handover apparatus of claim 22, wherein the handover request message includes a difference between an SNR of a interference-canceled signal and an SNR of the interference signal transmitted from each of the BSs.