System and method for supporting soft handover in a broadband wireless access communication system

• US 20060003767A1
• Filed: 06/15/2005
• Published: 01/05/2006
• Est. Priority Date: 06/15/2004
• Status: Active Grant

• Current Assignee: Nokia Technologies Oy (Nokia Corporation)
• Original Assignee: Samsung Electronics Co. Ltd.
• Inventors: Koo, Chang-Hoi, Lee, Sung-Jin, Son, Yeong-Moon, Kim, So-Hyun, Kang, Hyun-Jeong, Son, Jung-Je, Lim, Hyoung-Kyu
• Granted Patent: US 7,593,732 B2
• Time in Patent Office: Days
• US Class Current: 455/436
• CPC Class Codes: H04W 16/24 Cell structures
• CPC Class Codes: H04W 36/06 Reselecting a communication resource in the serving access point
• CPC Class Codes: H04W 36/18 for allowing seamless reselection, e.g. soft reselection

Abstract

A method for supporting handover in a BWA communication system is provided. The system includes an MS, a serving BS, and a plurality of neighbor BSs. The coverage area of each of the BSs is divided into sectors using different subcarrier bands. The MS collects information broadcast from the serving BS on the serving BS and the neighbor BS, measures a signal level for each of the sectors of the serving BS and the neighbor BSs according to the collected information, and sends a handover request based on the measured signal level for each of the sectors. The serving BS broadcasts information on the serving BS and the neighbor BS to the MS, determines if the MS can perform a soft handover from its current sector to another sector upon receiving the handover request from the MS, and permits the MS to perform the soft handover if possible.

Claims

1. A method for supporting a handover in a Broadband Wireless Access (BWA) communication system having a mobile station (MS), a serving base station (BS) from which the MS is currently receiving a service, and a plurality of neighbor BSs being different from the serving BS, the coverage area of each of the BSs being divided into sectors using different subchannel bands, the method comprising the steps of:

collecting, by the MS, information broadcasted from the serving BS on the serving BS and the neighbor BSs;

measuring a signal level for each of the sectors of the serving BS and the neighbor BSs according to the collected information;

sending a handover request to the serving BS based on the measured signal level for each of the sectors;

determining by the serving BS if the MS intends to perform a handover from a sector of the serving BS to another sector, based on the information included in the handover request; and

permitting the MS to perform soft handover.

2. The method of claim 1, wherein the step of performing soft handover comprises the steps of:

sending by the serving BS to the neighbor BS a notification indicating that the MS performs a handover over to the sector of the neighbor BS;

receiving from the neighbor BS a response indicating whether to approve handover of the MS;

if the response is affirmative, transmitting to the MS a handover response indicating that a soft handover to the neighbor BS is possible;

upon receiving the response, sending by the MSS to the serving BS a notification indicating that the MSS performs the handover; and

receiving downlink (DL)-MAP/uplink (UL)-MAP information from the serving BS and the neighbor BS, and exchanging data with corresponding sectors of the BSs.

3. The method of claim 2, further comprising the step of adding by the MS a sector having qualities that fall within a reference range to a soft active sector set.

4. The method of claim 3, wherein the soft active sector set is a set of possible sectors to which the MS can perform a soft handover.

5. The method of claim 1, wherein the MS transmits to the serving BS a handover request including information indicating if a soft handover to the sector of the neighbor BS or the sector of the serving BS is possible.

6. The method of claim 1, wherein the MS sends a handover request including an arrival time difference value between a preamble transmitted from the serving BS and a preamble transmitted from the neighbor BS.

7. The method of claim 6, wherein the serving BS determines to proceed with a soft handover of the MS if the arrival time difference value satisfies a predetermined range.

8. The method of claim 6, wherein unique preambles are transmitted from the sectors of the BSs.

9. A system for supporting a handover to a mobile station (MS) in a Broadband Wireless Access (BWA) communication system, the system comprising:

a serving base station (BS) from which the MS is currently receiving a service; and

a plurality of neighbor BSs being different from the serving BS, the coverage area of each of the BSs being divided into sectors using different subchannel bands,

wherein the MS collects periodically broadcast information on the serving BS, the neighbor BS, and the sectors, measures a signal level for each of the sectors of the serving BS and the neighbor BSs according to the collected information, and sends a handover request according to the measured signal level for each of the sectors, and

wherein the serving BS broadcasts information on the serving BS and the neighbor BS to the MS, determines if the MS can perform a soft handover from its current sector to another sector upon receiving the handover request from the MS, and permits the MS to perform a soft handover if possible.

10. The system of claim 9, wherein in order to perform a soft handover of the MS, the serving BS sends a notification indicating that the MS is to perform a handover to the sector of the neighbor BS, receives a response from the neighbor BS in response to the notification, transmits to the MS a handover response indicating that a soft handover to the neighbor BS is possible, if the response is affirmative, and receives from the MS a notification indicating that the MS performs soft handover.

11. The system of claim 9, wherein the MS receives a response from the serving BS in response to the handover request, sends to the serving BS a notification indicating that the MS is to perform a soft handover if information indicating that soft handover to the sector of the neighbor BS is possible is included in the response, receives downlink (DL)-MAP/uplink (UL)-MAP information from the serving BS and the neighbor BS, and performs ranging to a corresponding sector of the neighbor BS.

12. The system of claim 11, wherein the MS adds to a soft active sector set a sector of the neighbor BS that falls within a predetermined reference range.

13. The system of claim 12, wherein the soft active sector set is a set of possible sectors to which the MS can perform a soft handover.

14. The system of claim 9, wherein the MS sends a handover request including information indicating if soft handover to a sector of the neighbor BS is possible.

15. The system of claim 9, wherein the MS sends a handover request including an arrival time difference value between a preamble from the serving BS and a preamble from the neighbor BS.

16. The system of claim 9, wherein the serving BS determines soft handover of the MS if the arrival time difference value falls within a predetermined range.

17. The system of claim 9, wherein the unique preambles are transmitted from the sectors of the BSs.

18. A method for performing by a mobile station (MS) a handover from a sector of a serving base station (BS) to a sector of a neighbor BS in a Broadband Wireless Access (BWA) communication system having the MS, the serving BS from which the MS is currently receiving a service, and a plurality of neighbor BSs being different from the serving BS, the coverage area of each of the BSs being divided into sectors using different subchannel bands, the method comprising the steps of:

collecting information broadcast from the serving BS on the serving BS and the neighbor BSs;

measuring a signal level for each of the sectors of the serving BS and the neighbor BSs according to the collected information;

sending a handover request to the serving BS based on the measured signal level for each of the sectors;

receiving from the serving BS a handover response including sector information of a possible neighbor BS to which the MS can perform a soft handover to if a handover type determined in the serving BS is a soft handover;

sending to the serving BS a notification indicating that the MS is to perform a soft handover; and

performing ranging to a corresponding sector of the neighbor BS.

19. The method of claim 18, further comprising the step of adding to a soft active sector set a sector of the neighbor BS with reference parameters that fall within a predetermined reference range.

20. The method of claim 19, wherein the soft active sector set is a set of possible sectors to which the MS can perform soft handover.

21. A method for supporting a handover by a serving base station (BS) in a Broadband Wireless Access (BWA) communication system having a mobile station (MS), the serving BS from which the MS is currently receiving a service, and a plurality of neighbor BSs being different from the serving BS, a coverage area of each of the BSs being divided into sectors using different subchannel bands, the method comprising the steps of:

receiving a handover request from the MS;

determining if the MS can perform soft handover from a sector of the serving BS to another sector; and

permitting the MS to perform the soft handover if the MS can perform the soft handover from the sector of the serving BS to the sector of the neighbor BS.

22. The method of claim 21, wherein the step of performing the soft handover comprises the steps of:

sending to the neighbor BS a notification indicating that the MS is to perform a handover to the sector of the neighbor BS;

receiving from the neighbor BS a response indicating whether to approve handover;

transmitting to the MS a handover response indicating that the soft handover to the neighbor BS is possible, if the response is affirmative; and

receiving from the MS a notification indicating that the MS is to perform the soft handover.

23. The method of claim 21, wherein the serving BS receives from the MSS a handover request including information indicating if soft handover to the another sector is possible.

24. The method of claim 23, wherein the handover request received from the MS includes an arrival time difference value between a preamble from the serving BS and a preamble signal from the neighbor BS.

25. The method of claim 24, wherein the serving BS permits the MS to perform the soft handover if the arrival time difference value falls within a predetermined range.

26. The method of claim 24, wherein unique preambles are transmitted from the sectors of the BSs.