Patent Document

PRIORITY 
   This application claims the benefit under 35 U.S.C. 119(a) of a Korean Patent Application entitled “Apparatus And Method For Transmitting Wireless LAN Information In Mobile Communication Network For Wireless LAN Interworking”, filed with the Korean Intellectual Property Office on Aug. 14, 2004 and assigned Serial No. 2004-64134, the entire contents of which are hereby incorporated by reference. 
   BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates to interworking between a mobile communication network and a wireless local area network (WLAN). More particularly, the present invention relates to an apparatus and a method for transmitting WLAN information in a mobile communication network. 
   2. Description of the Related Art 
   Recently, as portable electronic appliances including portable computers and mobile phones have been rapidly developed, many studies and research have been performed in relation to wireless access schemes for a wired network, such as an Intranet, the Internet or the World Wide Web (WWW). A wireless local area network (WLAN) is known as a technology to access the wired network at a high rate with a low cost. In addition, 3 rd  generation mobile communication systems, such as the code division multiple access (CDMA) 2000, the wideband code division multiple access/universal mobile telecommunications system (WCDMA/UMTS), the general packet radio system (GPRS) or the evolution data and voice (1×EV-DV), may attain high rate data transmission through wireless channels so that the mobile station or user equipment can access the packet communication network, such as the Internet, through a cellular mobile communication network. 
   However, such advancements may cost a lot in wireless access technologies. For this reason, studies and research are currently focused on interworking terminals capable of accessing both the mobile communication network and the WLAN in order to attain interworking between the mobile communication network and the WLAN. The main purpose of the interworking is to provide services of the mobile communication network by using the WLAN, which is a mass storage network constructed at a low cost. 
   Differently from the mobile communication network, the IEEE 802.11 WLAN does not use a paging channel for tracking accessible network nodes, that is, access points. An operation of an IEEE 802.11 interworking terminal for detecting the access points is called a “scan”. The scan scheme of the WLAN may be divided into an active scan and a passive scan. According to the active scan, the terminal transmits a probe signal in order to probe access points in the vicinity of the terminal. Upon receiving the probe signal, the access point sends a response signal comprising various parameters required for accessing the access point, so that the terminal can recognize the access points. Although the terminal can rapidly find the access points by using the active scan, power consumption of the terminal may increase. According to the passive scan, the access points may transmit a beacon signal to a peripheral area thereof every several hundred milliseconds and the terminal receives the beacon signal, thereby recognizing the access points. Since the beacon signal comprises various parameters required for the terminal to access the WLAN, the terminal receiving the beacon signal can access the corresponding access point. Although the terminal employing the passive scan can reduce power consumption as compared with the terminal employing the active scan, the terminal cannot find the access points as rapidly. 
   In the case of a WLAN according to the IEEE 802.11 standard, it is difficult for the terminal to find the WLAN allowing access to the terminal, and in particular, a WLAN capable of interworking with the mobile communication network. That is, in order to scan all access points when the access points of the WLAN operate in mutually different frequency bands, the terminal must transmit probe signals through various frequency channels (active scan) or the terminal must search various frequency channels to receive the beacon signals of the frequency channels (passive scan). Thus, the time for finding a WLAN may increase. If the terminal continuously performs the scan operation to find a WLAN, power consumption of the terminal may significantly increase. 
   Therefore, the WLAN can provide an indicator for directing cells to perform the WLAN scanning by using system information broadcasted from the mobile communication network or can provide detailed WLAN information, for example, frequency information, a WLAN identifier: service set identifier (SSID) and the like for the purpose of fast WLAN scan. 
     FIG. 1  is a schematic view illustrating WLAN-interworking (WLAN-I) in a conventional mobile communication system. 
   Referring to  FIG. 1 , WLAN information  115  is transmitted by using system information broadcasted from a node B  100  provided in a cell  110  comprising a WLAN area  120 . Terminals  101  through  107  are WLAN-I terminals. The node B  100  provides the terminals  101  to  107  with the WLAN information  115  indicating that the WLAN area exists in the cell so that the terminals  101  to  107  scan the WLAN and then are handed over to the WLAN area  120 . 
   The WLAN area  120  is significantly smaller than the cell  110  of the mobile communication network. Thus, if the terminals  101  to  105  and  107  except for the terminal  106  adjacent to the WLAN area  120  perform the WLAN scanning, power consumption may unnecessarily increase. This problem may become severe as the size of the WLAN area  120  is reduced relative to the size of the cell  110 . In addition, although the WLAN area  120  is concentrated on a hot spot area in the cell, terminals located in other areas also perform the WLAN scan so that power consumption of the terminals may increase. In view of a network, the conventional mobile communication system transmits the WLAN information to the boundary area of the cell, in which the WLAN area  120  is not provided, so that transmission power is unnecessarily wasted. 
   SUMMARY OF THE INVENTION 
   Accordingly, the present invention has been made to solve the above-mentioned problems occurring in the prior art, and an object of the present invention is to provide an apparatus and a method capable of effectively transmitting WLAN information to a terminal in a mobile communication system without unnecessarily wasting power consumption in the mobile terminal. 
   Another object of the present invention is to provide an apparatus and a method for selectively transmitting WLAN-interworking (WLAN-I) information to a WLAN area by taking the direction of the WLAN in a cell and a distance between the WLAN area and a node B into consideration. 
   Still another object of the present invention is to provide an apparatus and a method for handling a direction of WLAN information transmission by using beam forming and for adjusting a radius of a WLAN area relative to a cell by using a separate code and transmission power different from those used for system information. 
   In order to accomplish these objects, according to one aspect of the present invention, a method is provided for transmitting wireless local area network (WLAN) information in a mobile communication network for WLAN-interworking. The method comprises the steps of setting a WLAN threshold value for determining if a WLAN area is present in a cell and a measurement period in system information, broadcasting the system information in the cell, and transmitting a common pilot channel, which indicates that the WLAN area is present in the cell, in a predetermined direction with predetermined transmission power to cover the WLAN area by using beam forming. 
   According to another aspect of the present invention, a method is provided for transmitting wireless local area network (WLAN) information in a mobile communication network for WLAN-interworking. The method comprises the steps of setting a WLAN threshold value for determining if a WLAN area is present in a cell in system information, broadcasting the system information in the cell, and transmitting a common pilot channel, which indicates that the WLAN area is present in the cell, with predetermined transmission power to cover the WLAN area. 
   According to still another aspect of the present invention, a method is provided for transmitting wireless local area network (WLAN) information in a mobile communication network for WLAN-interworking. The method comprises the steps of determining whether a WLAN area present in a cell has a directional characteristic and a radius characteristic relative to a base station (node B) provided in the cell, setting a WLAN scan indication, which indicates that the WLAN area is present in the cell, in the system information if the WLAN area has no directional characteristic and radius characteristic, and broadcasting the system information in the cell. 
   According to still yet another aspect of the present invention, a method is provided for transmitting wireless local area network (WLAN) information in a mobile communication network for WLAN-interworking. The method comprises the steps of receiving system information broadcasted in a cell and determining whether the system information includes a WLAN threshold value for determining if a WLAN area is present in the cell, as well as code information and a measurement period of a second common pilot channel, measuring a first common pilot channel and determining whether a measurement result of the first common pilot channel exceeds the WLAN threshold value if the system information includes the WLAN threshold value only, measuring a second common pilot channel and determining whether a measurement result of the second common pilot channel exceeds the WLAN threshold value if the system information comprises all of the code information and the measurement period of the second pilot channel and the WLAN threshold value, and initiating a WLAN scan if the measurement result of the first common pilot channel or the second common pilot channel exceeds the WLAN threshold value. 
   According to still yet another aspect of the present invention, an apparatus is provided for transceiving wireless local area network (WLAN) information in a mobile communication network for WLAN-interworking. The apparatus comprises a radio network controller for establishing a WLAN threshold value for determining if a WLAN area is present in a cell, and a measurement period in system information, broadcasting the system information in the cell, and transmitting a common pilot channel, which indicates that the WLAN area is present in the cell, in a predetermined direction with predetermined transmission power to cover the WLAN area by using beam forming, and a terminal for receiving the system information, determining whether the system information includes the WLAN threshold value as well as code information and a measurement period of the common pilot channel, measuring the common pilot channel, determining whether a measurement result of the common pilot channel exceeds the WLAN threshold value if the system information includes all of the code information and the measurement period of the second pilot channel and the WLAN threshold value, and initiating a WLAN scan if the measurement result of the common pilot channel exceeds the WLAN threshold value. 
   According to still yet another aspect of the present invention, an apparatus is provided for transceiving wireless local area network (WLAN) information in a mobile communication network for WLAN-interworking. The apparatus comprises a radio network controller establishing a WLAN threshold value for determining if a WLAN area is present in a cell, in system information, broadcasting the system information in the cell, and transmitting a common pilot channel, which indicates that the WLAN area is present in the cell, in a predetermined direction with predetermined transmission power to cover the WLAN area by using beam forming, and a terminal for receiving the system information, determining whether the system information includes the WLAN threshold value as well as code information and a measurement period of a second common pilot channel, measuring a first common pilot channel for distinguishing the cell, if the system information includes the WLAN threshold value only, determining whether a measurement result of the first common pilot channel exceeds the WLAN threshold value, and initiating a WLAN scan if the measurement result of the first common pilot channel exceeds the WLAN threshold value. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The above and other objects, features and advantages of the present invention will be more apparent from the following detailed description taken in conjunction with the accompanying drawings, in which: 
       FIG. 1  is a schematic view illustrating WLAN-I in a conventional mobile communication system; 
       FIG. 2  is a view illustrating WLAN information transmission according to an exemplary embodiment of the present invention; 
       FIG. 3  is a view illustrating WLAN information transmission according to an exemplary embodiment of the present invention; 
       FIGS. 4   a  and  4   b  are flowcharts illustrating the procedure of a RNC according to an exemplary embodiment of the present invention; and 
       FIG. 5  is a flowchart illustrating the operational procedure of a terminal according to an exemplary embodiment of the present invention. 
   

   Throughout the drawings, like reference numerals will be understood to refer to like parts, components and structures. 
   DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS 
   Hereinafter, exemplary embodiments of the present invention will be described with reference to the accompanying drawings. In the following description, a detailed description of known functions and configurations incorporated herein will be omitted for clarity and conciseness. The terms used in the following description are defined by taking functions thereof into consideration, so the terms may vary depending on customs or intentions of a user/administrator. Thus, definitions for the terms must be determined based on the whole contents of the present invention. 
     FIG. 2  is a view illustrating WLAN information transmission according to an exemplary embodiment of the present invention. 
   Referring to  FIG. 2 , a WLAN area  220  is located in a cell  210  with a directional characteristic relative to a node B  200 . 
   WLAN-interworking (WLAN-I) information is selectively transmitted to the WLAN area  220  located in the cell  210  by taking the direction of the WLAN area  220  in the cell  210  and the distance between the WLAN area  220  and a node B  200  into consideration. 
   Terminals  201  through  207  are WLAN-I terminals. The WLAN area  220  is located in a predetermined direction of the cell  210 , that is, in a 2 o&#39;clock direction. Accordingly, it is not necessary for the node B  200  to transmit the WLAN information in all directions of the cell  210 . 
   If the node B  200  indicates the terminal  206  of a start of the WLAN scan without detailed WLAN information, for example, frequency information, a WLAN identifier: service set identifier (SSID) and the like, the node B  200  carries a WLAN scan indication, which indicates the start of the WLAN scan, through a secondary common pilot channel (S-CPICH)  225  by using beam forming. 
   It is not necessary to transmit the S-CPICH  225  to the boundary area of the cell and transmission power for the S-CPICH  225  is determined according to the distance between the WLAN area  220  and the node B  200 . The terminal  206  periodically performs the S-CPICH measurement without continuously performing the WLAN scan in the cell. If a sufficient result of the S-CPICH measurement is obtained, the terminal  206  determines that the WLAN scan indication is detected, so the terminal  206  initiates the WLAN scan. 
   In order to implement the exemplary embodiment of the present invention, a channel code and a scrambling code of the S-CPICH, which may serve as the WLAN scan indication, are transmitted in the cell by using system information  215 . According to the current 3GPP standard, a code of spreading factor (SF) is used as the channel code and one of 15 secondary scrambling codes is used as the scrambling code. Thus, in order to allow the terminal  206  to analyze the S-CPICH which serves as the WLAN scan indication and is transmitted to the WLAN area  220  in the cell, the node B  200  indicates the terminal  206  of the channel code and the scrambling code used for the S-CPICH by using the system information  215  broadcasted in the cell. The channel code and the scrambling code may be indicated by using a corresponding index. If a scrambling code different from the above 15 secondary scrambling codes is used, the scrambling code can be directly indicated. In addition, the node B  200  can determine a WLAN_offset value and a WLAN_timer value for the S-CPICH measurement by using the system information  215  in order to allow the terminal  206  to determine if the result of the S-CPICH measurement is sufficient. 
   In contrast, if the node B  200  indicates the terminal  206  of detailed WLAN information such as frequency information, WLAN identifier (SSID), the WLAN information is transmitted to the WLAN area  220  together with the S-CPICH  225  by using a specific code. At this time, the WLAN information is transmitted to the WLAN area  220  with reduced transmission power by using beam forming. At this time, the system information  215  comprises information related to the channel for transmitting the WLAN information in addition to S-CPICH information. The terminal  206  primarily receives the S-CPICH  225 . If reception power for the S-CPICH  225  is sufficient, the terminal  206  receives the WLAN information according to channel information comprised in the system information  215 . 
   In the meantime, it is also possible that the node B  200  indicates the terminal  206  of the detailed WLAN information for the WLAN area  220 , which is WLAN frequency information, WLAN identifier (SSID) and the like by using the system information  215  and transmits the WLAN scan indication through the S-CPICH. 
     FIG. 3  is a view illustrating WLAN information transmission according to another exemplary embodiment of the present invention. Referring to  FIG. 3 , a WLAN area  320  is located in a cell  310  without the directional characteristic relative to a node B  300 . The exemplary embodiment of the present invention as shown in  FIG. 3  is embodied when the WLAN area  320  is adjacent to the node B  300 . 
   Terminals  301  through  307  are WLAN-I terminals. Since the WLAN area  320  is located in the cell  310  without the directional characteristic relative to the node B  300 , the node B may not use the beam forming scheme. In addition, since the WLAN area  320  is located adjacent to the node B  300 , if the node B  300  directs the terminals provided in the cell  310  to perform the WLAN scan by using system information  315 , the terminals except for the terminal  302  may unnecessarily perform the WLAN scan and waste power. Therefore, the node B  300  does not use the beam forming scheme related to the directional characteristic of the WLAN scan, but may transmit the WLAN scan indication through a S-CPICH  325  with reduced transmission power according to the distance between the WLAN area  320  and the node B  300 . 
   Thus, WLAN-offset and WLAN_timer, which are code information of the S-CPICH which serves as the WLAN scan indication, are transmitted to the terminals  301  through  307  by using the system information  315 . Accordingly, the S-CPICH  325  can be transmitted against all directions of the cell  310  with reduced transmission power without using the beam forming scheme. Therefore, the terminals  301  and  303  through  307  may attain insufficient measurement results with respect to the S-CPICH  325 , so they do not perform the WLAN scan. If the node B  300  indicates the terminal  302  of the detailed WLAN information, such as frequency information, WLAN identifier (SSID), of the WLAN area  320 , the node B  300  may transmits the WLAN information to the WLAN area  220  by using a specific code or by adding the WLAN information to the system information  315 . 
   In the meantime, if the WLAN area  320  does not have directional characteristics relative to the node B  300  as shown in  FIG. 3 , the node B  300  may allow the terminal  302  to perform the WLAN scan based on the WLAN_offset value without using the S-CPICH while preventing the WLAN scan of other terminals  301  and  303  through  307  remote from the WLAN area  320 . At this time, the node B  300  may not separately establish the S-CPICH which serves as the WLAN scan indication, but properly determine the WLAN_offset value and transmit the WLAN_offset value by using the system information  315 . In addition, the terminal uses the WLAN_offset value as a threshold value for the measurement result of the P-CPICH, which is a common pilot channel. In addition, the node B  300  transmits the WLAN scan indication or detailed WLAN information by using system information. 
     FIGS. 4   a  and  4   b  are flowcharts illustrating the procedure of a radio network controller (RNC) according to an exemplary embodiment of the present invention, in which  FIG. 4   a  shows transmission of system information and  FIG. 4   b  shows transmission of a S-CPICH. 
   Step  401  shown in  FIG. 4   a  represents initialization of WLAN-I. In step  402 , the RNC determines whether the WLAN area has a radius characteristic only in the cell without the directional characteristic. If it is determined in step  402  that the WLAN area has the radius characteristic only in the cell, the RNC establishes the WLAN_offset value, which is used as a threshold value of the P-CPICH, in the system information. However, if it is determined in step  402  that the WLAN area does not have radius characteristic only in the cell, step  403  is performed in order to determine if the WLAN area has the directional characteristic. 
   If it is determined in step  403  that the WLAN area has the directional characteristic, the RNC establishes the S-CPICH for transmitting the WLAN scan indication, WLAN_offset serving as the threshold value of the S-CPICH and WLAN_timer, which is a periodic value for the S-CPICH measurement, in the system information. However, if it is determined in step  403  that the WLAN area does not have directional characteristic in the cell, it indicates that the WLAN area does not have both the radius characteristic and the directional characteristic in the cell. This may happen when a plurality of WLAN areas is irregularly provided in the cell. Thus, the RNC sets the WLAN scan indication in the system information in step  404  and then performs step  412 . 
   In step  412 , the system information established in steps  411 ,  421  and  404  is broadcasted in the cell. 
   Referring to  FIG. 4   b , the RNC determines whether the WLAN area has the radius characteristic only in the cell in step  413 . If it is determined in step  413  that the WLAN area has the radius characteristic only in the cell, there is no need for action in step  431 . 
   However, if it is determined in step  413  that the WLAN area does not have the radius characteristic only in the cell, step  414  is performed. In step  414 , the RNC determines whether the WLAN area has the directional characteristic relative to the node B in the cell. If it is determined in step  414  that the WLAN area has the directional characteristic relative to the node B in the cell, the WLAN scan indication is transmitted through the S-CPICH by using the beam forming to cover the WLAN area in step  441 . However, if it is determined in step  414  that the WLAN area has no directional characteristic, step  415  is performed. 
   In step  415 , the RNC determines whether the WLAN area has both the directional characteristic and the radius characteristic in the cell. If it is determined in step  415  that the WLAN area has both the directional characteristic and the radius characteristic in the cell, the WLAN scan indication is transmitted through the S-CPICH by using the beam forming with reduced transmission power to cover the WLAN area in step  451 . However, if it is determined in step  415  that the WLAN area has no directional and radius characteristics in the cell, the RNC may not perform an action in step  461 . 
     FIG. 5  is a flowchart illustrating the operational procedure of a terminal according to an exemplary embodiment of the present. 
   The terminal reads the system information in the cell in step  501  and determines whether the WLAN scan indication is present in the system information in step  502 . If the system information comprises the WLAN scan indication, the terminal initiates the WLAN scan in step  503 . However, if the system information does not comprise the WLAN scan indication, step  511  is performed in order to determine whether only the WLAN_offset is present in the system information. If the system information includes only the WLAN_offset, the terminal measures the P-CPICH in step  512  and determines whether the measurement result is greater than the WLAN_offset value in step  513 . If the measurement result is greater than the WLAN_offset value, the terminal initiates the WLAN scan in step  531 . However, if the measurement result is less than the WLAN_offset value, the procedure returns to step  512 . 
   In the meantime, if it is determined in step  511  that the system information does not exclusively have the WLAN_offset, the terminal determines whether the S-CPICH information used as the WLAN scan indication, WLAN_offset information and WLAN_timer information are present in the system information in step  521 . If the system information includes all of the S-CPICH information, WLAN_offset information and WLAN_timer information, the terminal measures the S-CPICH in step  541 . However, if the system information does not include all of the S-CPICH information, WLAN_offset information and WLAN_timer information, the terminal determines that there is no cell for the WLAN or area for the WLAN-I in step  522 . 
   In addition, the terminal determines whether the measurement result of the S-CPICH is greater than the WLAN_offset value in step  542 . If the measurement result of the S-CPICH is greater than the WLAN_offset value, the terminal initiates the WLAN scan in step  551 . However, if the measurement results of the S-CPICH is less than the WLAN_offset value, the WLAN_timer starts and the terminal waits for expiration of the WLAN_timer in step  543 . Then, the procedure returns to step  541 . 
   As described above, according to the exemplary embodiments of the present invention, the WLAN information is locally transmitted to the area adjacent to the WLAN area by taking the directional characteristic of the WLAN area in the cell and the distance between the WLAN area and the node B into consideration. Thus, the terminals can initiate the WLAN scan with optimized conditions. In addition, in view of the network, it is not necessary to transmit the WLAN information over the whole area of the cell, so transmission power of the terminals can be saved. 
   While the invention has been shown and described with reference to certain exemplary embodiments thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention as defined by the appended claims.

Technology Category: h