Abstract:
There is disclosed a method for performing channel assignment in a base station for a mobile communication system. Upon receipt of a request for assigning a channel to a mobile station, a base station transceiver system (BTS) generates a connect message including channel information, which indicates a Walsh code, out of 256 Walsh codes, to be used for a channel to be assigned to the mobile station, and a quasi-orthogonal function (QOF) index. The BTS transmits the generated connect message to a base station controller (BSC). The BSC generates a connect ACK message for acknowledging the channel assignment-related information included in the connect message and transmits the generated connect ACK message to the BTS. Upon receipt of the connect ACK message, in the BTS assigns the channel that was acknowledged by the BSC to the mobile station.

Description:
This application claims the benefit of Provisional Application No. 60/133,790, filed May 12, 1999. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates generally to a CDMA (Code Division Multiple Access) mobile communication system, and in particular, to a method for providing 4 quasi-orthogonal functions (QOF), which are used in association with 256 Walsh codes in a forward link, in a base station transceiver system (BTS) and a base station controller (BSC). 
     2. Description of the Related Art 
     Existing IS-95A/B CDMA communication systems spread a radio channel with a Walsh function. However, as the IS-2000 standard introduces new channels to the forward and reverse links, the existing conventional communication system lacks the necessary amount of Walsh codes to maintain orthogonality between channels. 
     Accordingly, there is a need for a method for increasing the number of the channels, without decreasing the orthogonality between the existing channels. For the IS-2000 forward link, several methods have been proposed. One method is to define a quasi-orthogonal function (QOF) necessary for the mobile station thereby to assign 4 times the channels as compared with the case when the existing Walsh function is used, and another method is to expand the existing Walsh function which can generate 64 Walsh codes, so as to generate 256 Walsh codes. The quasi-orthogonal function (QOF) is commonly applied to IS-2000 forward channels, such as the fundamental channel (FCH), the dedicated control channel (DCCH) and the supplemental channel (SCH). However, existing base stations can only support 64 Walsh code channels. 
     Now, reference will be made to the types of the channels used in the IMT-2000 (International Mobile Telecommunications 2000) standard. IMT-2000 includes UMTS (Universal Mobile Telecommunication Service) and CDMA-2000/IS-2000. 
     Every channel is divided into a physical channel and a logical channel. The logical channel is established over the physical channel, and several logical channels can be established on a single physical channel. If the physical channel is released, the logical channel established over the physical channel is automatically released. It is not necessary to establish another physical channel in order to establish a certain logical channel. When a physical channel to be established for a logical channel is already established for another logical channel, the only required operation is to assign this logical channel to the previously established physical channel. 
     The physical channel can be divided into dedicated channels and common channels according to its characteristics. Dedicated channels are exclusively used for communication between the BTS and a particular mobile station (MS), and include a fundamental channel (FCH), a dedicated control channel (DCCH) and a supplemental channel (SCH). The fundamental channel is used to transmit voice, data and signaling signals. Such a fundamental channel is compatible with TIA/EIA-95-B. The dedicated control channel is used to transmit data and signaling signals. The dedicated control channel supports a discontinuous transmission (DTX) mode in which data is only transmitted when the upper layer generates transmission data. Because of this property, the dedicated control channel is suitable for effectively providing a packet service. The supplemental channel is used to transmit large amounts of data. 
     In addition to the dedicated channels stated above, the physical channel includes a common channel which is used in common by the base station and several mobile stations. A physical channel for the forward link transmitted from the BTS to the MS is called a paging channel, and a physical channel for the reverse link transmitted from the MS to the BTS is called an access channel. These common channels are compatible with IS-95B. 
     The logical channels to be assigned on the above physical channels include a dedicated signaling channel (dsch) and a dedicated traffic channel (dtch). The dedicated signaling channel can be assigned to the fundamental channel and the dedicated control channel, which are physical channels. The dedicated traffic channel can be assigned to the fundamental channel, the dedicated control channel and the supplemental channel. The dedicated signaling channel is used when the base station and the mobile station exchange a control signal. The dedicated traffic channel is used when the base station and the mobile station exchange user data. 
     The common logical channel to be assigned on the common physical channel is divided into a common signaling channel (csch) used to transmit control signal, and a common traffic channel (ctch) use to transmit user data. The common logical channels are assigned on the paging channel for the forward link, and are assigned on the access channel for the reverse link. 
       FIG. 1  shows a structure of a general mobile communication system. More specifically,  FIG. 1  shows a reference model of a 3G IOS (Interoperability Specifications) for a digital air interface between a mobile switching center (MSC) and a base station, and between base stations in the common mobile communication system. 
     Referring to  FIG. 1 , between MSC  20  and BSC  32 , a signal is defined as an A 1  interface and user information is defined as an A 2 /A 5  (circuit data) interface. An A 3  interface is defined to connect a target BS  40  to a frame selection/distribution unit (SDU) function block  34  of a source BS  30  for soft/softer handoff between base stations. The signaling and user traffic between the target BS  40  and the SDU function block  34  of the source BS  30  are transmitted through the A 3  interface. An A 7  interface is defined for signal exchange between the target BS  40  and the source BS  30 , for soft/softer handoff between the base stations. In the CDMA mobile communication system, a wired communication link between the base station  30  and the base station  40 , and between the base station  30  and the MSC  20 , is comprised of a forward link transmitted from the MSC  20  to the base station  30 , a reverse link transmitted from the base station  30  to the MSC  20 . Generally, a wired bi-directional line connected between the MSC  20  and the base station  30  carries the forward and reverse links. The MSC  20  includes a call control and mobility management block  22  and a switching block  24 . Further, the MSC  20  is connected to a data network such as the Internet through an interworking function (IWF) block  50 . The wired line exists over all the interfaces in the RAN, e.g., MSC-BSC, BS-BS, BSC-BTS, BSC-Target BTS and so on. 
       FIG. 2  shows a procedure for exchanging signals between the BTS and the BSC (more specifically, the SDU function block in the BSC, BSC-SDU) according to the prior art. The operation can be performed either between the BSC  32  (or BSC-SDU  34 ) and the BTS  36  in the source BS  30 , or between the BSC  42  and the BTS  44  in the target BS  40 .  FIG. 2  is independent of types of the required physical channel, i.e., DCCH, FCH, SCH or whatever. That is, the invention in this document can be applied to all types of physical channels. 
     Referring to  FIG. 2 , the BTS determines forward and reverse channels to be established with the MS and then generates a signaling message (more specifically, a connect message) necessary for channel establishment, in step  201 . The generated signaling message includes a frame selector (or channel type) and channel information. The detailed operation of step  201  will be described later with reference to FIG.  3 . The BTS sends the generated connect message to the BSC in step  203 . Upon receipt of the connect message, the BSC analyzes the received connect message to check the channel assigned to the MS, and generates a connect ACK message to be transmitted to the BTS, in step  205 . The detailed operation of receiving the connect message will be described later with reference to FIG.  4 . The BSC sends the generated connect ACK message to the BTS in step  207 . The connect ACK message includes information for acknowledging establishment of the channel requested by the BTS. The BTS then assigns the acknowledged channel to the MS in step  209 . 
     Summarizing the operation of  FIG. 2 , the BTS generates the connect message including information about a channel to be assigned to the MS and sends the generated connect message to the BSC. Upon receipt of the connect message, the BSC processes the received connect message, generates the connect ACK message for acknowledging channel assignment and sends the generated connect ACK message to the BTS. The BTS then assigns the acknowledged channel to the MS. 
       FIG. 3  shows a detailed procedure for transmitting the connect message according to the prior art. This operation is performed when the BTS transmits the connect message to the BSC-SDU when it is required to assign a channel to the MS. The structures of the connect message transmitted from the BTS to the BSC-SDU are shown in  FIGS. 5A and 5B . 
     Referring to  FIG. 3 , the BTS determines in step  301  whether the channel to be assigned to the MS is a supplemental code channel (SCCH). SCCH is the IS-2000 defined name corresponding to IS-95B SCH (Supplemental Channel). IS-2000 is on the evolution path of IS-95A/B. IS-2000 also has the IS-95 A/B channels in order to maintain backward compatibility. It is determined in step  301  that the channel to be assigned to the MS is SCCH, the BTS sets (designates) in step  303  the frame selector (or channel type) in the connect message, whose structure is shown in  FIGS. 5A and 5B , to IS-95B SCCH, so as to enable the BSC to recognize that the channel to be assigned is an IS-95B channel, and then designates a Walsh code with 6-bit channel information. Thereafter, in step  305 , the BTS ignores an information element overlapped due to establishment of the IS-95A/B fundamental channel in the connect message, whose structure is shown in  FIGS. 5A and 5B . Cell Information, Extended Handoff Parameters in the A 3  Connect Information element are overlapped with those in the same Connect message used when IS-95 A/B FCH is newly established. IS-95B SCCH establishment procedure follows the IS-95 A/B FCH establishment procedure. IS-95B SCCH has to be established in parallel to IS-95A/B FCH under the same cell. The BTS fills all other information elements to complete the connect message, and then transmits the connect message to the BSC. Here, in a handoff (HO) situation, the BTS fills all the handoff-related information element. 
     If it is determined in step  301  that the channel to be assigned to the MS is not SCCH, the BTS designates in step  307  the frame selector (or channel type) in the connect message shown in  FIGS. 5A and 5B  to the fundamental channel, so as to enable the BSC to recognize that the channel to be assigned is an IS-95B fundamental channel, and then designates a Walsh code with 6-bit channel information. Thereafter, in step  309 , the BTS fills all the information elements in the connect message of  FIGS. 5A and 5B  to complete the connect message, and then transmits the connect message to the BSC. Here, in the handoff (HO) situation, the BTS fills all the handoff-related information element. 
       FIG. 4  shows a procedure for receiving the connect message according to the prior art. This operation is performed when the BSC-SDU receives the connect message for requesting channel assignment, transmitted from the BTS, and generates a connect ACK message for the connect message. 
     Referring to  FIG. 4 , the BSC-SDU receives the connect message for requesting channel assignment from the BTS in step  401 . In step  401 , the BSC-SDU analyzes the received connect message, and examines the establishment-requested channel in the message of  FIGS. 5A and 5B  and an identifier of a traffic channel between the BTS and BSC. The BSC-SDU assigns the traffic channel between the BSC and BTS, corresponding to the radio channel, in step  403 . As a result, channel connection among BSC-BTS-MS is completed. Further, in step  405 , the BTS-SDU fills all the information elements of the connect ACK message shown in FIG.  6  and transmits it to the BTS. 
     A simplified structure of the connect ACK message shown in  FIG. 6  will be described with reference to Table 1 below. 
     
       
         
               
               
               
               
             
           
               
                   
                 TABLE 1 
               
               
                   
                   
               
               
                   
                 Information Element 
                 Element Direction 
                 Type 
               
               
                   
                   
               
             
             
               
                   
                 Message Type II 
                 BTS &gt; SDU 
                 M 
               
               
                   
                 Call Connection Reference 
                 BTS &gt; SDU 
                 0 
               
               
                   
                 Correlation ID 
                 BTS &gt; SDU 
                 0 
               
               
                   
                 SDU ID 
                 BTS &gt; SDU 
                 0 
               
               
                   
                 A3 Connect Information 
                 BTS &gt; SDU 
                 0 
               
               
                   
                   
               
               
                   
                 M: Mandatory,   
               
               
                   
                 O: Optional,   
               
               
                   
                 R: Recommend,   
               
               
                   
                 C: Conditionally Recommend   
               
             
          
         
       
     
     The connect message shown in Table 1 is an A 3  message transmitted when the target BS  40  initiates or adds one or more A 3  user traffic connections to the SDU  34  of the source BS  30 . The A 3  message includes the following information. 
     Message Type II: an information element indicating A 3 /A 7  message type. 
     Call Connection Reference: an information element for uniquely defining a call connection over all zones. This value is always maintained during call connection over every handoff. 
     Correlation ID: an information element used to correlate a request message with a response message for the request message. 
     SDU ID: an information element for identifying a specific SDU instance in one SDU node. 
     A 3  Connect Information: an information element used to add one or more cells to one new A 3  connection or existing A 3  connection. This information element field is shown in Table 2 below, and 4 th  to (j−1)th octets of Table 2 include Cell Information Record fields of Table 3 below. 
     
       
         
               
               
               
               
               
               
               
               
               
             
               
               
             
               
               
               
               
             
               
               
             
               
               
               
               
             
           
               
                 TABLE 2 
               
               
                   
               
               
                 7 
                 6 
                 5 
                 4 
                 3 
                 2 
                 1 
                 0 
                 Octet 
               
               
                   
               
             
             
               
                   
               
             
          
           
               
                 A3/A7 Element Identifier 
                 1 
               
             
          
           
               
                 Reserved 
                 Framed Selector Index 
                 New A3 
                 2 
               
               
                   
                   
                 Indicator 
               
               
                   
                 Length of Cell Info Record 
                   
                 3 
               
               
                   
                 Cell Info Record-1 st  octet 
                   
                 4 
               
               
                   
                 Cell Info Record-2 nd  octet 
                   
                 5 
               
               
                   
                 . . . 
                   
                 6 
               
               
                   
                 Cell Info Record-last octet 
                   
                 . . . 
               
               
                   
                 Length of Traffic Circuit ID 
                   
                 j 
               
               
                 (MSB) 
                 Traffic Circuit ID 
                   
                 j + 1 
               
               
                   
                 . . . 
                   
                 j + 2 
               
               
                   
                 . . . 
                   
                 . . . 
               
               
                   
                   
                 (LSB) 
                 k 
               
             
          
           
               
                 Extended Handoff Direction Parameters Field Length 
                 k + 1 
               
               
                 Extended Handoff Direction Parameters-1 st  cell, 1 st  octet 
                 k + 2 
               
               
                 . . . 
                 . . . 
               
               
                 Extended Handoff Direction Parameters-1 st  cell, last octet 
                 1 
               
               
                 . . . 
                 . . . 
               
               
                 Extended Handoff Direction Parameters-last cell, 1 st  octet 
                 m 
               
               
                 . . . 
                 . . . 
               
               
                 Extended Handoff Direction Parameters-last cell, last octet 
                 n 
               
             
          
           
               
                   
                 Length of Channel Element ID 
                   
                 n + 1 
               
               
                 (MSB) 
                 Channel Element ID-1 st  octet 
                   
                 n + 2 
               
               
                   
                 . . . 
                   
                 . . . 
               
               
                   
                   
                 (LSB) 
                 p 
               
               
                   
               
             
          
         
       
     
     
       
         
               
               
               
               
               
               
               
               
               
             
               
               
             
               
               
               
               
               
             
               
               
               
             
               
               
             
               
               
               
               
               
             
               
               
               
             
           
               
                 TABLE 3 
               
               
                   
               
               
                 7 
                 6 
                 5 
                 4 
                 3 
                 2 
                 1 
                 0 
                 Octet 
               
               
                   
               
             
             
               
                   
               
             
          
           
               
                 A3/A7 Element Identifier 
                 1 
               
               
                 Length 
                 2 
               
               
                 Cell Identification Discriminator 1 
                 3 
               
               
                 Cell Identification 
                 Vari- 
               
               
                   
                 able 
               
             
          
           
               
                 Reserved 
                 New Cell 
                 PWR —   
                 (MSB) 
                 j 
               
               
                   
                 Indicator 
                 Comb_Ind 
               
             
          
           
               
                 Pilot_PN 1 
                 (LSB) 
                 j + 1 
               
               
                 Code_Chan 1 
                   
                 j + 2 
               
               
                 . . . 
                   
                 . . . 
               
             
          
           
               
                 Cell Identification Discriminator n 
                 k 
               
               
                 Cell Identification n 
                 Vari- 
               
               
                   
                 able 
               
             
          
           
               
                 Reserved 
                 New Cell 
                 PWR —   
                 (MSB) 
                 1 
               
               
                   
                 Indicator 
                 Comb_Ind 
               
             
          
           
               
                 Pilot_PN n 
                 (LSB) 
                 l + 1 
               
               
                 Code_Chan n 
                   
                 1 + 2 
               
               
                   
               
             
          
         
       
     
     Table 3 shows a message including air interface channel information for the cells attached to one call leg, and each field is defined as follows. 
     Length: the number of octets of the elements following a Length field. 
     Cell Identification Discriminator: a value used to describe the formats following a Cell Identification field according to cells. 
     Cell Identification: identification of the cells relating to A 3  connection. 
     Reserved: this value is set to ‘00000’. 
     New Cell Indicator: a field indicating whether a corresponding cell is a cell newly added to A 3  traffic connection in the present procedure or a cell which previously exists in A 3  connection. 
     PWR_Comb_Ind: a power control symbol combining indicator. The BTS sets this field to ‘1’, if a forward traffic channel relating to the corresponding pilot transmits the same bits as closed-loop power control subchannel bits of a previous pilot in this message. Otherwise, the BTS sets this field to ‘0’. When this record occurs first in this element, the BTS sets this field to ‘0’. 
     Pilot_PN: this field includes a PN sequence offset corresponding to the related cell and is set in a unit of 64 PN chips. 
     Code_Chan: this field includes a code channel index corresponding to the related cell. The BTS sets a value used on the forward traffic channel in connection with a designated pilot to one of 0 to 63. 
     A simplified structure of the connect ACK message shown in  FIG. 6  will be described with reference to Table 4 below. 
     
       
         
               
               
               
               
             
           
               
                   
                 TABLE 4 
               
               
                   
                   
               
               
                   
                 Information Element 
                 Element Direction 
                 Type 
               
               
                   
                   
               
             
             
               
                   
                 Message Type II 
                 SDU &gt; BTS 
                 M 
               
               
                   
                 Call Connection Reference 
                 SDU &gt; BTS 
                 0 
               
               
                   
                 Correlation ID 
                 SDU &gt; BTS 
                 0 
               
               
                   
                 A3 Connect Information 
                 SDU &gt; BTS 
                 0 
               
               
                   
                   
               
               
                   
                 M: Mandatory,         
               
               
                   
                 O: Optional,   
               
               
                   
                 R: Recommend,   
               
               
                   
                 C: Conditionally Recommend   
               
             
          
         
       
     
     The connect ACK message of Table 4 is an A 3  message for transmitting A 3 -CDMA Long Code Transition Directive results performed on the A 3  signaling interface from the target BS  40  to the SDU  34  of the source BS  30 . Further, an A 3  CDMA Long Code Transition Directive Ack message for the A 3  CDMA Long Code Transition Directive of Table 4 is shown in Table 5 below. 
     
       
         
               
               
               
             
           
               
                 TABLE 5 
               
               
                   
               
               
                 Information Element 
                 Element Direction 
                 Type 
               
               
                   
               
             
             
               
                 Message Type II 
                 BTS &gt; SDU 
                 M 
               
               
                 Call Connection Reference 
                 BTS &gt; SDU 
                 0 
               
               
                 Cell Information Record (Committed) 
                 BTS &gt; SDU 
                 0 
               
               
                 SDU ID 
                 BTS &gt; SDU 
                 0 
               
               
                 PMC Cause 
                 BTS &gt; SDU 
                 0 
               
               
                 Cell Information Record (Uncommitted) 
                 BTS &gt; SDU 
                 0 
               
               
                   
               
               
                 M: Mandatory,   
               
               
                 O: Optional,   
               
               
                 R: Recommend,   
               
               
                 C: Conditionally Recommend   
               
             
          
         
       
     
     The A 3  CDMA Long Code Transition Directive Ack message of Table 5 includes the following information elements. 
     Message Type II: an information element indicating an A 3 /A 7  message type. 
     Call Connection Reference: an information element for uniquely defining a call connection over all zones. This value is always maintained during call connection over every handoff. 
     SDU ID: an information element for identifying a specific SDU instance in one SDU node. 
     PMC Cause: an information element indicating failed results of A 3 /A 7  message. 
     Cell Information Record (Committed, Uncommitted): a Cell Information Record field of Table 3 is used, as it is. This is an information element including air interface channel information for the cells attached to one call leg. When successful, this field is set to ‘Committed’, and when failed, this field is set to ‘Uncommitted’. This field is used together with the PMC Cause field. 
     Problems of the existing channel assignment method will be described based on the foregoing descriptions. 
     As described with reference to Tables 1 to 5, in the conventional 3G IOS radio channel information, the quasi-orthogonal function (QOF) specified in the CDMA-2000 standard is not defined. Further, only 64 Walsh codes of 0 to 63 are supported for the code channels. Thus, when the base station does not support the quasi-orthogonal function (QOF) which is necessary for the mobile station, the 3G forward radio channel cannot be assigned in the mobile station. Therefore, it is necessary to define a message field which can support the quasi-orthogonal function (QOF) and 256 Walsh codes for the radio channel information in the existing 3G IOS. 
     SUMMARY OF THE INVENTION 
     It is, therefore, an object of the present invention to provide a method for expanding existing 64 supportable Walsh codes to 256 Walsh codes and supporting a quasi-orthogonal function (QOF) for a forward channel in a base station of a mobile communication system. 
     To achieve the above objects, there is provided a method for performing channel assignment in a base station for a mobile communication system. Upon receipt of a request for assigning a channel to a mobile station, a base station transceiver system (BTS) generates a connect message including channel information indicating a Walsh code to be used for a channel to be assigned to the mobile station, out of 256 Walsh codes, and information indicating a quasi-orthogonal function (QOF) index, and transmits the generated connect message to a base station controller (BSC). The BTS generates a connect ACK message for acknowledging the channel assignment-related information included in the connect message and transmits the generated connect ACK message to the BSC. Upon receipt of the connect ACK message, in the BTS assigns a channel acknowledged by the BSC to the mobile station. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The above and other objects, features and advantages of the present invention will become more apparent from the following detailed description when taken in conjunction with the accompanying drawings in which: 
         FIG. 1  is a diagram illustrating a reference model of a 3G IOS (Interoperability Specification) for a digital air interface between a mobile switching center (MSC) and a base station (BS), and between the base stations in a common mobile communication system; 
         FIG. 2  is a flow diagram illustrating a procedure for exchanging signals between a base station transceiver system (BTS) and a base station controller (BSC) for radio channel assignment according to the prior art; 
         FIG. 3  is a flow chart illustrating a procedure for transmitting a connect message according to the prior art, wherein the BTS transmits the connect message to the BSC-SDU when it is necessary to assign a channel to a mobile station (MS); 
         FIG. 4  is a flow chart illustrating a procedure for receiving the connect message according to the prior art, wherein the BSC-SDU receives the connect message for requesting channel assignment, transmitted from the BTS, and generates a connect ACK message for the connect message; 
         FIGS. 5A through 5D  are diagrams illustrating the connect message transmitted from the BTS to the BSC according to the prior art; 
         FIG. 6  is a diagram illustrating the connect ACK message transmitted from the BSC to the BTS according to the prior art; and 
         FIG. 7  is a flow chart illustrating a procedure for transmitting a connect message according to a preferred embodiment of the present invention, wherein the BTS transmits the connect message to the BSC-SDU when it is necessary to assign a channel to the MS. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     A preferred embodiment of the present invention will be described herein below with reference to the accompanying drawings. In the following description, well-known functions or constructions are not described in detail since they would obscure the invention in unnecessary detail. 
     In an exemplary embodiment of the invention, a base station supports a quasi-orthogonal function (QOF), defined by IS-2000, necessary for the mobile station and 256 Walsh codes, in addition to the maximum 64 code channels defined by the existing IS-95A/B. 
       FIG. 7  shows a procedure for transmitting a connect message according to a preferred embodiment of the present invention. In this procedure, the BTS transmits the connect message to BSC-SDU when it is necessary to assign a channel to the MS. A detailed structure of the Cell Information Record included in the connect message transmitted from the BTS to the BSC-SDU will be described later with reference to FIG.  6 . 
     Referring to  FIG. 7 , the BTS determines in step  701  whether a channel to be assigned to the MS is SCCH. If it is determined in step  701  that the channel to be assigned is SCCH, the BTS designates in step  713  the frame selector (or channel type) shown in  FIG. 6  to ‘IS-95B SCCH’ so as to enable the BSC to recognize that the channel to be assigned is an IS-95B channel, and designates a Walsh code with 6-bit channel information. Then, in step  715 , the BTS ignores the information elements overlapped due to establishment of IS-2000 FCH RC ½in the connect message shown in  FIG. 5 , fills all the remaining elements to generate (or complete) the connect message, and transmits the generated connect message to the BSC. Here, in the handoff situation, the BTS fills the handoff-related information elements to complete the connect message, and transmits the connect message to the BSC. 
     If it is determined to step  701  that the channel to be assigned is not SCCH, the BTS determines in step  703  whether the channel to be assigned is a supplemental channel (SCH). If it is determined in step  703  that the channel to be assigned is the supplemental channel, the BTS determines in step  707  whether to perform QOF masking on the channel to be assigned. 
     If it is determined in step  707  that QOF masking should be performed on the channel, the BTS designates in step  717  the frame selector (or channel type) shown in  FIG. 6  to ‘SCH’ so as to enable the BSC to recognize that the channel to be assigned is a supplemental channel. Further, the BTS designates the channel information indicating a Walsh code to be assigned to the channel (with 8 bits or 11 bits). 8 bits can support up to 256 Walsh Codes. However, IS-2000 uses 11 bits for specifying Walsh Codes even if the present IS-2000 can only support up to 256 Walsh Codes. The remaining 3 bits are prepared for the future extension. For compliance with IS-2000, 11 bits is acceptable. But just 8 bits are sufficient for the present need. The BTS then designates a QOF mask index (=01,10,11) corresponding to the Quasi orthogonal function codes to be assigned. Then, in step  719 , the BTS ignores the information elements overlapped due to the establishment of the fundamental channel (FCH) and the dedicated control channel (DCCH) in the connect message shown in  FIG. 5 , fills all the remaining elements to complete the connect message, and transmits the connect message to the BSC. Here, in the handoff situation, the BTS fills the handoff-related information elements of the message shown in  FIG. 5  to complete the connect message, and transmits the connect message to the BSC. 
     If it is determined in step  707  that QOF masking should not be performed on the channel to be assigned, the BTS designates in step  721  the frame selector (or channel type) to ‘SCH’ so as to enable the BSC to recognize that the channel to be assigned is a supplemental channel. Further, the BTS designates the channel information indicating a Walsh code to be assigned to the channel bit number (8 bits or 11 bits) of IS-2000, and then sets the QOF mask index ‘00’. Here, the QOF mask index is set to ‘00’, since QOF masking should not be performed. Then, in step  723 , the BTS ignores the information elements overlapped due to establishment of the fundamental channel (FCH) and the dedicated control channel (DCCH) in the connect message shown in  FIG. 5 , fills all the remaining elements to complete the connect message, and transmits the connect message to the BSC. Here, in the handoff situation, the BTS fills the handoff-related information elements of the message shown in  FIG. 5  to complete the connect message, and transmits the connect message to the BSC. 
     Meanwhile, if it is determined in step  703  that the channel to be assigned is not the supplemental channel, the BTS determines in step  705  whether the channel to be assigned is a fundamental channel (FCH). If it is determined in step  705  that the channel to be assigned is a fundamental channel, the BTS examines in step  709  whether QOF masking should be performed on the channel to be assigned. 
     If it is determined in step  709  that QOF masking should be performed on the channel, the BTS designates in step  725  the frame selector (or channel type) shown in  FIG. 6  to ‘FCH’ so as to enable the BSC to recognize that the channel to be assigned is a fundamental channel. Further, the BTS designates the channel information indicating a Walsh code to be assigned to the channel bit number (8 bits or 11 bits) of IS-2000, and then designates a QOF mask index (=01, 10,11) corresponding to the Quasi orthogonal function codes to be assigned. Then, in step  727 , the BTS fills all the information elements included in the connect message shown in  FIG. 5  to complete the connect message, and transmits the connect message to the BSC. Here, in the handoff situation, the BTS fills the handoff-related information elements of the message shown in  FIG. 5  to complete the connect message, and transmits the connect message to the BSC. 
     If it is determined in step  709  that QOF masking should not be performed on the channel to the assigned, the BTS designates in step  729  the frame selector (or channel type) to ‘FCH’ so as to enable the BSC to recognize that the channel to be assigned is a fundamental channel. Further, the BTS designates the channel information indicating a Walsh code to be assigned to the channel bit number (8 bits or 11 bits) of IS-2000 and then sets the QOF mask index to ‘00’. Here, the QOF mask index is set to ‘00’, since QOF masking should not be performed. Then, in step  731 , the BTS fills all the information elements included in the connect message shown in  FIG. 5  to complete the connect message, and transmits the connect message to the BSC. Here, in the handoff situation, the BTS fills the handoff-related information elements of the message shown in  FIG. 5  to complete the connect message, and transmits the connect message to the BSC. 
     However, if it is determined in step  705  that the channel to be assigned is not the fundamental channel, the BTS determines in step  711  whether QOF masking should be performed on the channel to be assigned. If it is determined in step  711  that QOF masking should be performed on the channel, the BTS designates in step  733  the frame selector (or channel type) shown in  FIG. 6  to ‘DCCH’ so as to enable the BSC to recognize that the channel to be assigned is a dedicated control channel. Further, the BTS designates the channel information indicating a Walsh code to be assigned to the channel bit number (8 bits or 11 bits) of IS-2000, and then designates a QOF mask index (=01,10,11) corresponding to the Quasi orthogonal function codes to be assigned. Then, in step  735 , the BTS fills all the information elements included in the connect message shown in  FIG. 5  to complete the connect message, and transmits the connect message to the BSC. Here, in the handoff situation, the BTS fills the handoff-related information elements of the message shown in  FIG. 5  to complete the connect message, and transmits the connect message to the BSC. 
     If it is determined in step  711  that QOF masking should not be performed on the channel to be assigned, the BTS designates in step  737  the frame selector (or channel type) to ‘DCCH’ so as to enable the BSC to recognize that the channel to be assigned is a dedicated control channel. Further, the BTS designates the channel information indicating a Walsh code to be assigned to the channel bit number (8 bits or 11 bits) of IS-2000, and then sets the QOF mask index to ‘00’. Here, the QOF mask index is set to ‘00’, since QOF masking should not be performed. Then, in step  739 , the BTS fills all the information elements included in the connect message shown in  FIG. 5  to complete the connect message, and transmits the connect message to the BSC. Here, in the handoff situation, the BTS fills the handoff-related information elements of the message shown in  FIG. 5  to complete the connect message, and transmits the connect message to the BSC. 
     Table 6 below shows the detailed structure of Cell Information Record for supporting the quasi-orthogonal function (QOF) and the 256 Walsh codes. The Cell Information Record includes a QOF MASK field for recording the QOF mask index according to the present invention and a Code_Chan field for designating 256 Walsh codes. Upon receipt of the connect message including the above fields, the BSC analyzes the channel assignment-related information recorded in the above fields, and then transmits a connect ACK message including ACK information for the connect message. Upon receipt of the connect ACK message, the BTS assigns the channel to the MS. 
     
       
         
               
               
               
               
               
               
               
               
               
             
               
               
             
               
               
               
               
               
               
             
               
               
               
             
               
               
             
               
               
               
               
               
               
             
               
               
               
             
           
               
                 TABLE 6 
               
               
                   
               
               
                 7 
                 6 
                 5 
                 4 
                 3 
                 2 
                 1 
                 0 
                 Octet 
               
               
                   
               
             
             
               
                   
               
             
          
           
               
                 A3/A7 Element Identifier 
                 1 
               
               
                 Length 
                 2 
               
               
                 Cell Identification Discriminator 1 
                 3 
               
               
                 Cell Identification 
                 Vari- 
               
               
                   
                 able 
               
             
          
           
               
                 Reserved 
                 QOF MASK 
                 New Cell 
                 PWR —   
                 (MSB) 
                 j 
               
               
                 (3 bits) 
                   
                 Indicator 
                 Comb_Ind 
               
             
          
           
               
                 Pilot_PN 1 
                 (LSB) 
                 j + 1 
               
               
                 Code_Chan 1(0-255) 
                   
                 j + 2 
               
               
                 . . . 
                 . . . 
               
             
          
           
               
                 Cell Identification Discriminator n 
                 k 
               
               
                 Cell Identification n 
                 Vari- 
               
               
                   
                 able 
               
             
          
           
               
                 Reserved 
                 QOF MASK 
                 New Cell 
                 PWR —   
                 (MSB) 
                 l 
               
               
                 (3 bits) 
                   
                 Indicator 
                 Comb_Ind 
               
             
          
           
               
                 Pilot_PN 1 
                 (LSB) 
                 l + 1 
               
               
                 Code_Chan 1(0-255) 
                   
                 l + 2 
               
               
                   
               
             
          
         
       
     
     As described above, the present invention provides a signaling message and a procedure for processing the signaling message such that the base station can support the quasi-orthogonal function (QOF) necessary for the mobile station. In this manner, the base station and the mobile switching center can assign 256 Walsh codes for the radio channels. 
     While the invention has been shown and described with reference to a certain preferred embodiment 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.