1. Field of the Invention
The present invention relates to a broadband wireless access communication system, and more particularly to a system and a method for configuring a neighbor base station advertisement (hereinafter referred to as ‘MOB_NBR-ADV’) message including neighbor base station information.
2. Description of the Related Art
In a next generation communication system, that is, a 4th generation (hereinafter referred to as ‘4G’) communication system, much research has been undertaken to provide users with services which have various qualities of service (hereinafter referred to as ‘QoS’) and to support a transmission speed of about 100 Mbps. Particularly, in the current 4G communication system, research is being vigorously pursued to support high-speed services to broadband wireless access (hereinafter referred to as ‘BWA’) communication systems such as wireless local area network (hereinafter referred to as ‘WLAN’) communication systems and wireless metropolitan area network (hereinafter referred to as ‘WMAN’) communication systems by ensuring both mobility and various QoSs. A typical communication system for this purpose is an IEEE (Institute of Electrical and Electronics Engineers) 802.16 communication system.
The IEEE 802.16 communication system is a communication system which applies an orthogonal frequency division multiplexing (hereinafter referred to as ‘OFDM’)/orthogonal frequency division multiple access (hereinafter referred to as ‘OFDMA’) scheme in order to support a broadband transmission network to a physical channel of the WMAN system.
A structure of an IEEE 802.16 communication system will now be described with reference to FIG. 1, which schematically illustrates the common IEEE 802.16e communication system.
Referring to FIG. 1, the IEEE 802/16e communication system has a multiple cell structure, for example, it has cells 100 and 150. The IEEE 802.16e communication system also includes a base station (hereinafter referred to as ‘BS’) 110 controlling the cell 100, a BS 140 controlling the cell 150, and a plurality of mobile stations (hereinafter referred to as ‘MS’) 111, 113, 130, 151, and 153. Signal transmission/reception between the BSs 110, 140 and the MSs 111, 113, 130, 151, and 153 is implemented using the OFDM/OFDMA scheme. In addition, from among the MSs 111, 113, 130, 151, and 153, the MS 130 exists in a boundary area between the cells 100 and 150, that is, a handover area. Thus, the BS 100 or the BS 150 must be capable of supporting handover of the MS 130.
For example, when the MS 130 moves to an area covered by the cell 150 while it communicates with the BS 110 in the cell 100, and the MS 130 undergoes handover to the BS 140, the MS 130 must conduct a network re-entry procedure with the BS 140. This is because the BS 110 and the BS 140 have different physical layers and different medium access control (hereinafter referred to as ‘MAC’) layer structures.
If an MS conducts a network re-entry procedure during handover from a serving BS, in which the MS is currently located, to a neighbor BS as stated above, a data service in transmission/reception is interrupted and must newly be started after the MS completes the handover to the neighbor BS. In order to handover to the neighbor BS in this way, the MS must be capable of recognizing neighbor BS information. The neighbor BS information may be recognized by receiving an MOB_NBR-ADV message which each BS periodically broadcasts.
Hereinafter, an MOB-NBR-ADV message format will be described with reference to FIGS. 2A and 2D, which illustrate a format of a common MOB_NBR-ADV message.
Referring to FIGS. 2A and 2D, the MOB_NBR-ADV message is configured of a plurality of information elements (hereinafter referred to as ‘IE’), and the IEs are as follows:                Management Message Type: represents the type of a transmitted message:        Operator ID: represents an unique identifier assigned to a operator,        Configuration Change Count: each time message configuration changes, increases by 1 to indicate whether a corresponding message has changed;        Fragmentation Index: represents the number of times that a message is transmitted when the MOB_NBR-ADV message is fragmented and the fragmented messages are separately transmitted;        Total Fragmentation: represents the total number of fragmented messages;        Skip-Optional-Fields Flag: indicates a BS-ID when the BS-ID is omitted in a corresponding message;        N-NEIGHBORS: represents information on how many neighbor BSs are included in a current message; that is, it represents the number of neighbor BSs;        Length: represents information field length according to BS-Ids;        PHY Profile ID: indicates an information ID of a radio channel used in a corresponding BS;        FA Index: indicates an inherent ID representing a frequency allocated to a corresponding BS;        BS EIRP: represents transmission power intensity of a corresponding BS;        Neighbor BS-ID: indicates IDs of neighbor BSs;        Preamble Index: indicates an ID of a preamble to be used in a corresponding sector of a corresponding BS;        HO Process Optimization: dividedly indicates information about indispensable procedures and information about omissible procedures during handover to a corresponding BS;        Scheduling Service Supported: indicates QoS classes supportable by a corresponding BS, from among various QoS classes predefined between BSs;        Available Radio Resource: indicates the degree of availability of radio channel resources of a corresponding BS;        Handoff Neighbor Preference: defines the degree of logical preference when a serving BS controls an MS to handover to a neighbor BS;        DCD Configuration Change Count: indicates the DCD (Downlink Channel Descriptor) information serial number of a corresponding neighbor BS;        UCD Configuration Change Count: indicates the UCD (Uplink Channel Descriptor) information serial number of a corresponding neighbor BS;        Other neighbor information (hereinafter referred to as ‘TLV (Type/Length/Value) Encoded Neighbor Information’): represents all information related to a neighbor BS other than the aforementioned information.        
Now, the MOB_NBR-ADV message will be described in more detail.
The MS, having received the MOB_NBR-ADV message periodically broadcasted from the serving BS, can acquire scanning information for measuring signal intensities of neighbor BSs. The MS can identify neighbor BSs by using Neighbor BS-ID information included in the MOB_NBR-ADV message, and thus comes to recognize physical frequency band search information, which is necessary for scanning the neighbor BSs, through the Physical Frequency field. In this way, the serving BS periodically broadcasts the MOB_NBR-ADV message to provide information which the MS requires for handover.
Therefore, the conventional MOB_NBR-ADV message includes a lot of information, and its large size is problematic.
Here, the MS may require, or may not necessarily require, the information included in the MOB_NBR-ADV depending on the present circumstances. Also, the MOB_NBR-ADV message is not a message which is transmitted to a specific MS, but is a broadcast message which is repeatedly transmitted to many unspecified MSs in very short cycles. On account of this, bandwidth consumption in a radio channel section is very large. In the end, there is a problem in that radio channel resources are wasted because a network operator must include unnecessary information in the MOB_NBR-ADV message.