Method for supporting fast base station switching in a wireless communication system using multiple frequency bands

A method for performing fast base station switching in an mobile station capable of using multiple frequency assignments in a wireless communication system are provided, in which initial network entry to a base station managing at least two frequency assignments is performed in one of the at least two frequency assignments, overlay mode support information and FA information about the at least two frequency assignments are acquired by the initial network entry, the overlay mode support information indicating whether the base station supports multiple frequency assignments, the base station is notified that the mobile station will operate in an overlay mode using multiple frequency assignments based on the acquired information, and signals are transmitted and received to and from the base station in the at least two frequency assignments.

The present application claims the benefit under 35 U.S.C. §119(a) of a Korean Patent Application filed in the Korean Intellectual Property Office on Mar. 26, 2007 and assigned Serial No. 2007-29446 and a Korean Patent Application filed in the Korean Intellectual Property Office on Apr. 20, 2007 and assigned Serial No. 2007-39064, the entire disclosure of both of which is hereby incorporated by reference.

TECHNICAL FIELD OF THE INVENTION

The present invention generally relates to a wireless communication system using multiple frequency bands. More particularly, the present invention relates to a method for supporting Fast Base Station Switching (FBSS).

BACKGROUND OF THE INVENTION

Along with the development of wireless communication systems, more services and more service data are required. To meet the demands, a broadband wireless mobile communication system has emerged. However, due to limited frequency resources, the wireless mobile communication system has limited frequency bands. Accordingly, there exists a need for increasing frequency bands available for providing broadband services.

FIG. 1illustrates a single-frequency band supporting structure and a two-frequency band supporting structure in a conventional wireless mobile communication system.

In a wireless mobile communication system, especially based on Institute of Electrical and Electronics Engineers (IEEE) 802.16, a base station (BS) manages one or more frequency assignments and provides a service to a mobile station (MS) in at least one of the frequency assignments.

Referring toFIG. 1, a mobile station (MS)100can switch from a first frequency assignment (FA)120(FA1) to a second frequency assignment (FA)140(FA2). If the MS100is limited to only one FA or different base stations manage the two FAs120and140, the MS100receives a service in FA2by an inter-FA handover.

If an MS150can operate in two or more FAs or the same base station (BS) manages two FAs160and180(FA1and FA2), the MS150can receive a service in the FAs160and180. In this manner, signal transmission and reception between an MS and a BS in multiple FAs is favorable for high-speed, large-data transmission and reception. However, a procedure for using multiple FAs between the MS and the BS is yet to be specified. Also, a technique for enabling the MS to fast switch from a current FA to a new FA or from a serving BS to another BS is to be developed.

SUMMARY OF THE INVENTION

To address the above-discussed deficiencies of the prior art, it is a primary aspect of exemplary embodiments of the present invention is to address at least the problems and/or disadvantages and to provide at least the advantages described below. Accordingly, an aspect of exemplary embodiments of the present invention is to provide a method for using multiple frequency bands in a wireless communication system.

Another aspect of exemplary embodiments of the present invention provides a method for supporting fast base station (BS) switching or fast frequency band switching in a wireless communication system using multiple frequency bands.

In accordance with an aspect of exemplary embodiments of the present invention, there is provided a method for performing fast base station switching in a mobile station (MS) capable of using multiple frequency assignments in a wireless communication system, in which initial network entry to a base station managing at least two frequency assignments is performed in one of the at least two frequency assignments, overlay mode support information and frequency assignment (FA) information about the at least two frequency assignments are acquired by the initial network entry, the overlay mode support information indicating whether the base station supports multiple frequency assignments, the base station is notified that the mobile station will operate in an overlay mode using multiple frequency assignments based on the acquired information, and signals are transmitted and received to and from the base station in the at least two frequency assignments.

In accordance with another aspect of exemplary embodiments of the present invention, there is provided a method for performing fast base station switching in a mobile station capable of using multiple frequency assignments in a wireless communication system having base stations each managing at least two frequency assignments, in which neighbor base station information including a frequency assignment (FA) list of a neighbor base station is received from a serving base station, total frequency assignments are scanned using the FA list, a target frequency assignment is determined according to a result of the scanning, a switch indication including information about the selected target frequency assignment is transmitted to the serving base station, the target frequency assignment is switched to, overlay mode information is received in the target frequency assignment, a base station managing the target frequency assignment is notified that the mobile station will operate in an overlay mode, and signals are transmitted and received in the target frequency assignment and another frequency assignment of the base station managing the target frequency assignment.

In accordance with a further aspect of exemplary embodiments of the present invention, there is provided a method for supporting fast base station switching in a serving base station that provides a service to a mobile station in a wireless communication system having base stations each managing at least two frequency assignments, in which frequency assignment (FA) lists are exchanged with neighbor base stations, neighbor base station information including the FA lists is transmitted to the mobile station, information indicating whether the mobile station supports an overlay mode and information about a service level that the mobile station wants are exchanged with the neighbor base stations, and upon receipt of a switch indication including a target frequency assignment from the mobile station, a base station managing the target frequency assignment is notified of the target frequency assignment.

In accordance with still another aspect of exemplary embodiments of the present invention, there is provided a method for supporting fast base station switching in a neighbor base station in a wireless communication system having base stations each managing at least two frequency assignments, in which frequency assignment (FA lists are exchanged with a serving base station and other neighbor base stations, a signal indicating that a mobile station will perform fast base station switching to a target frequency assignment managed by the neighbor base station is received from the serving base station, switching is performed with the mobile station in the target frequency assignment, overlay mode information is transmitted to the mobile station in the target frequency assignment, the overlay mode information including information about a primary frequency assignment and a secondary frequency assignment for use in signal transmission and reception to and from the mobile station, and signals are transmitted to and from the mobile station in the primary frequency assignment and the secondary frequency assignment.

DETAILED DESCRIPTION OF THE INVENTION

Exemplary embodiments of the present invention provide a method for supporting fast base station switching (FBSS) in a wireless mobile communication system using multiple frequency bands. The frequency bands can be frequency assignments. Herein, “overlay mode” is defined as a mode in which data can be transmitted and received between a mobile station (MS) and a base station (BS) in multiple frequency bands (i.e., frequency assignments). While the present invention is described in the context of an IEEE 802.16 communication system, it is to be clearly understood that it is also applicable to other communication systems including Mobile Worldwide Interoperability for Microwave Access (WiMAX).

FIG. 2is a diagram illustrating a signal flow for an overlay mode supporting procedure according to an exemplary embodiment of the present invention.

Referring toFIG. 2, a base station (BS)240manages a first frequency assignment (FA)250(FA1) having a first base station identifier (BSID1) and a second FA260(FA2) having a second base station identifier (BSID2). A mobile station (MS)200performs initial network entry to the BS240in FA1in step201. By the initial network entry, the MS200can acquire overlay mode support information and FA information. The initial network entry will be detailed below.

The MS200acquires synchronization to the BS240in FA1and then performs initial ranging to the BS240by exchanging ranging messages.

The MS200transmits a Subscriber Basic Capability REQuest (SBC-REQ) message to the BS240. The SBC-REQ message may include information about whether the MS200supports the overlay mode and information indicating the maximum number of supported FAs in the overlay mode. The information can be included in a REGistration-REQuest (REG-REQ) message used during registration, instead of the SBC-REQ message.

The BS240replies to the MS200with a Subscriber Basic Capability ReSPonse (SBC-RSP) message for the SBC-REQ message. The SBC-RSP message may include information about whether the BS230supports the overlay mode and information indicating the number of FAs supported by the BS240. The SBC-RSP message may further include information about the indexes of all FAs managed by the BS240and center frequency and synchronization information about each FA, or only information about as many FAs as supported for the MS200.

Instead of the SBC-RSP message, the above information can be transmitted in a REGistration-ReSPonse (REG-RSP) message used during the registration. Then the BS240and the MS200perform authentication and registration.

After completing the initial network entry, the MS200transmits in FA1to the BS240an overlay mode notification signal indicating that it will operate in the overlay mode in steps203and205. Since both the MS200and the BS240support the overlay mode, the MS200is aware that the overlay mode is available and transmits the overlay mode notification signal to the BS240in FA1. The overlay mode notification signal can be a Bandwidth Request (BR) header with a BR field set to ‘0’ or a separately procured Medium Access Control (MAC) control message.

While the MS200notifies the BS240that it will operate in the overlay mode after the initial network entry in the above description, it can notify the BS of an overlay mode start time during the initial network entry.

In the illustrated case ofFIG. 2, the MS200notifies the BS240of the overlay mode operation in FA1in steps203and205. Yet, it can be further contemplated that the MS200notifies the BS240of the overlay mode operation in FA2after raging in FA2. In this case, data transmission and reception between the MS200and the BS240may be in progress in FA1. When the MS200determines that data transmission and reception in FA2is possible, it can notify the BS240of the overlay mode operation. For example, upon successful completion of the ranging to the BS240in FA2, the MS can notify the BS240that it will operate in the overlay mode.

In steps207and209, the MS200and the BS240transmit and receive data with each other in FA1and FA2.

Meanwhile, the BS240can allocate a Channel Quality Information (CQI) channel in FA1to the MS200in order to determine the channel statuses of FA1and FA2of the MS200. The MS200reports the channel qualities of FA1and FA2on the allocated CQI channel in steps211to217. The MS200may transmit an FBSS-related signal on the CQI channel and may report the CQIs in a MAC control message without being allocated the CQI channel, which will be described in detail with reference toFIG. 3.

FIG. 3is a diagram illustrating a signal flow for an FBSS supporting procedure in a multiple-FA system according to another exemplary embodiment of the present invention.

Referring toFIG. 3, an MS300belongs to a first BS320(BS1), which is thus a serving BS, and BS1manages two FAs. Second and third BSs340and360(BS2and BS3) are neighbor BSs to BS1, each managing two FAs.

BS1exchanges BS information periodically with BS2340and BS3360in steps301and303. The BS information includes an FA list of the BS that has transmitted the BS information. The FA list lists the indexes and center frequencies of FAs.

In step305, the BS1transmits neighbor BS information in a first FA (FA1)325to the MS300. The neighbor BS information also includes information about the BS1.

The MS300scans BS1320, BS2340and BS3360by measuring the signal strengths of BS1320, BS2340and BS3360based on the neighbor BS information in step307. The scanning results can be Signal-to-Noise Ratios (SNRs). In step309, the MS300transmits a diversity set update request message to the BS1320according to the scanning results. The diversity set update request message includes FAs that the MS300wants to include in its diversity set. Hence, a plurality of FAs managed by the same or different BSs can be included in the diversity set update request message. Also, the BS can request the diversity update to the MS and the BS-initiated diversity update is performed in a similar manner to the MS-initiated diversity update.

Upon receipt of the diversity set update request message, the BS1320exchanges FBSS-related backbone information with neighbor BSs managing the FAs included in the diversity set update request message in step311. The FBSS-related backbone information includes information indicating whether the MS300can support the overlay mode, the maximum number of FAs available to the MS300, and service level information for the MS. The FBSS-related backbone information may further include information about a CQI channel to be allocated to the MS300. The service level information indicates a service level that the MS300can achieve when BS1transmits data in all FAs used for communications with the MS300and service levels that the MS300can achieve when BS2340and BS3360transmit data in all FAs that they can support for the MS300.

In step313, the BS1320transmits a diversity set update response message to the MS300in FA1325. The MS300transmits in FA1325to the BS1320a diversity set update indication message indicating that the diversity set has been updated in step315.

Meanwhile, if the diversity set update request message includes information about a plurality of FAs managed by each of BS1320, BS2340and BS3360, the BS1320selects one FA per BS and includes the selected FAs in the diversity set update response message.

In step317, the MS300reports the CQIs of the FAs included in the diversity set to the BS1320on a CQI channel allocated by FA1325. If the MS300determines that it needs to switch to one of the FAs included in the diversity set as a result of monitoring the FAs, it transmits a switch indication message to the BS1320on the CQI channel in step319. Herein, it is assumed that the MS300wants to switch to a first FA (FA1)345of BS2, having a third BSID (BSID3). Hence, the switch indication message includes BSID3.

The BS1320notifies the BS2340that the MS300will switch to FA1345with BSID3over a backbone network in step321. If a CQI channel for use in communications by FA1345having BSID3has not been allocated to the MS300yet, the BS1320acquires information about the CQI from the BS2340and transmits the CQI channel information to the MS300by Anchor_Switch_IE in step323. The structure of Anchor_Switch_IE is disclosed in an IEEE 802.16 standard document.

In step325, the MS300switches to FA1345of the BS2340. The BS2transmits overlay mode information to the MS300in FA1345in step327. The overlay mode information provides at least one of information indicating whether the BS2will use the overlay mode, information about a primary FA and second FAS when the overlay mode is supported, information about the number of FAs to be used in the overlay mode, information about the indexes and center frequencies of the FAs, and information about a start frame in which the overlay mode will start. The overlay mode information is delivered to the MS300in an extended subheader or a MAC control message. The primary FA is FA1345of the BS2340. If the BS2340manages at least three FAs, the number of secondary FAs will increase.

The MS300notifies the BS2340that it will operate in the overlay mode by transmitting a BR header with a BR field set to 0 or a MAC control message in FA1345in step329. Then the MS300transmits and receives data to and from the BS2340in FA1345and a second FA (FA2)350in step331.

While the MS300notifies BS2that it will operate in the overlay mode in FA1345of BS2in step329, it can be further contemplated that the MS300notifies the BS2340of the overlay mode operation in FA2350or any other secondary FA of the BS2340. In this case, the MS300performs ranging to the BS2340in FA2350or any other secondary FA when needed. Upon successful completion of the ranging, the MS300can notify the BS2340of the overlay mode operation in FA2or any other secondary FA. In this case, data transmission and reception between the MS300and the BS2340may be in progress in FA1.

Meanwhile, if the MS300wants to switch to a second FA (FA2)330of the BS1320, that is, a secondary FA of BS1, or if switching between a primary FA and a secondary FA is required within BS1, BS1can re-establish a data path to the MS300in the primary FA or the secondary FA. That is, when FA2330is set as the primary FA of the MS300inFIG. 3, the data path established in the old primary FA (i.e., FA1325) is released and a data path is established in FA2330. Or instead of establishing the data path in FA2330, a connection in FA2330can be provided by utilizing the data path in FA1325.

FIG. 4is a flowchart illustrating an FBSS operation of an MS according to the present invention.

Referring toFIG. 4, the MS acquires an FA list from its serving BS in step402. The FA list includes information about the indexes and center frequencies of FAs. The MS scans the FAs in step404and updates a diversity set by a diversity set updating procedure with the serving BS in step406. The diversity set updating procedure can be requested by the MS or the BS.

In step408, the MS reports the CQIs of the FAs to the serving BS. The MS indicates connection switching to a target BS to the serving BS in step410. The target BS can be the serving BS or a neighbor BS of the serving BS. In step412, the MS switches to the target BS, that is, it performs an FBSS.

The MS receives overlay mode information from the target BS in step414and notifies the target BS that it will operate in the overlay mode in step416. In step418, the MS transmits and receives data in a plurality of FAs managed by the target BS.

FIG. 5is a flowchart illustrating an FBSS-related operation of a serving BS according to the present invention.

Referring toFIG. 5, the serving BS exchanges BS information with neighbor BSs in step502. The neighbor information includes the FA list of each BS. The serving BS transmits neighbor BS information including the FA lists in step504. If the serving BS receives a diversity set update request from the MS or it transmits the diversity set update request to the MS, it exchanges FBSS-related backbone information with the neighbor BSs in step506.

Upon receipt of a switch indication indicating switching to a particular target BS from the MS in step508, the serving BS exchanges FBBS-related backbone information with the target BS in step510and transmits information about a CQI channel allocated by the target BS to the MS in step512.

FIG. 6is a flowchart illustrating an FBSS-related operation of an FBSS-target BS according to the present invention.

Referring toFIG. 6, the target BS exchanges FBSS-related backbone information with a serving BS in step602. The FBSS-related backbone information may include overlay mode support information and service level information. The target BS performs switching with an MS in a primary FA, FA1in step604and transmits overlay mode information to the MS in step606. In step608, the target BS is notified from the MS that the MS will operate in the overlay mode. The target BS transmits and receives data to and from the MS in the primary FA and a secondary FA in step610.

As is apparent from the above description, the present invention advantageously enables seamless service provisioning by supporting FBSS for an MS in a wireless communication system.