Patent ID: 7593732
Filing Date: 2009-09-22
Classification: H04W

Abstract:
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; sending, by the MS, a scan request message to the serving BS; sending, by the serving BS to the MS, a scan response message including a signal quality measurement method for measuring signals from the serving BS and the neighbor BSs in response to the scan request message; measuring, by the MS, a signal level for each of the sectors of the serving BS and the neighbor BSs according to the collected information and the scan response message; adding, by the MS, a second sector of a neighbor BS having quality that satisfies a reference range to a soft active sector set; sending, by the MS, a handover request message including the measured signal level for each of the sectors, an arrival time difference indication field indicating whether soft handover is supported and whether an arrival time difference value is included in the handover request message, and the arrival time difference value being between a preamble transmitted from the serving BS and a preamble transmitted from the neighbor BS, wherein the arrival time difference value is included in the handover request message if a value of the arrival time difference indication field indicates that it is possible to support soft handover of the MS; determining, by the serving BS, if the MS intends to perform a handover from a first sector of the serving BS to the second sector of the neighbor BS, based on the measured signal level, the arrival time difference indication field and the arrival time difference value included in the handover request message; sending, by the serving BS, to the MS, a handover response message to permit the MS to perform the soft handover according to the determining result, when the serving BS determines to proceed with a soft handover of the MS if the arrival time difference value satisfies a predetermined range; sending, by the MS, a handover indication message including a handover indication type field indicating a target BS is deleted or added in the soft active sector set and an identifier of the target BS; and receiving, by the MS, a first downlink (DL)-MAP/uplink (UL)-MAP message from the first sector of the serving BS and a second DL-MAP/UL-MAP message from the second sector on the neighbor BS after sending the handover indication message.