Abstract:
An apparatus and method for a Mobile Station (MS) in an idle mode for performing a location update in a broadband wireless access communication system is provided. The method includes transmitting a ranging request message requesting location update to a Base Station (BS) when a location update condition is met in idle mode, receiving a ranging response message including information for location update response from the BS, and wherein the information indicates whether a downlink traffic is pending for the MS.

Description:
PRIORITY 
     This application claims priority under 35 U.S.C. §119 to an application filed in the Korean Intellectual Property Office on May 30, 2006 and assigned Serial No. 2006-48605, the contents of which are incorporated herein by reference. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates generally to a Broadband Wireless Access (BWA) communication system, and in particular, to an apparatus and a method for fast processing downlink traffic that has been generated during a location update procedure in an idle-mode Mobile Station (MS). 
     2. Description of the Related Art 
     Provisioning of services with diverse Quality of Service (QoS) requirements at or above 100 Mbps to users is an active study area for a future-generation communication system called a 4 th  Generation (4G) communication system. Particularly, active research is conducted on provisioning of high-speed service by ensuring mobility and QoS to a BWA communication system such as a Wireless Local Area Network (WLAN) and a Wireless Metropolitan Area Network (WMAN). Examples of such systems are Institute of Electrical and Electronics Engineers (IEEE) 802.16a and IEEE 802.16e systems. 
     According to the IEEE 802.16e standards, an idle-mode MS shall update its location, if any of a plurality of location update conditions is met. The IEEE 802.16e-2005 standard defines four location update conditions: Zone Update according to change of paging group, Timer Update, Power Down Update, and Medium Access Control (MAC) Hash Skip Threshold Update. 
     Before describing the location update conditions, it is to be clarified that Downlink Channel Descriptor (DCD), Uplink Channel Descriptor (UCD), Mobile Paging Advertisement (MOB_PAG-ADV), Paging Group Identifier (PG-ID), MAC Hash Skip Threshold, MAC Hash Skip Counter, Deregistration Command (DREG-CMD), Ranging Request (RNG-REQ), and Ranging Response (RNG-RSP) messages are in compliance with the IEEE 802.16e-2005 standard. 
     In Zone Update according to change of paging group, the MS performs a location update process when it detects a change in its paging group by comparing a PG-ID stored in the MS with a PG-ID included in a DCD or MOB_PAG-ADV message broadcasted by a preferred BS during a Paging Listening Interval (PLI) known to the MS. If the two PG-IDs are different, the MS determines that its paging group has been changed. 
     In Timer Update, the MS periodically performs the location update process prior to the expiration of an idle-mode timer. The idle-mode timer is set to 128 to 65536 seconds as defined in IEEE 802.16e-2005 Parameters and Constants. 
     In Power Down Update, the MS attempts a location update as part of its orderly power-down procedure. As the MS informs its power-down to a paging controller being a network entity that handles the idle mode of the MS, the paging controller deletes information about the MS. 
     In MAC Hash Skip Threshold Update, the MS performs the location update process if an MS MAC Hash Skip Counter exceeds a MAC Hash Skip Threshold. The MAC Hash Skip Threshold is known from a DREG-CMD message that the MS receives from a network in order to enter the idle mode. When the location update is successful, the MS and the BS need to initialize their MAC Hash Skip Counters. 
     A description will be made of  FIG. 1 , which is a flowchart illustrating a conventional location update process when a preferred BS is changed within the same paging group. 
     Referring to  FIG. 1 , a first BS  110  and a second BS  120  are in the same paging group. When the first BS  110  is a preferred BS, an MS  100  monitors occurrence of a location update event in idle mode in step  130 . Upon occurrence of a location update event, the MS  100  updates its location with the first BS  110  in step  132  and proceeds to step  134 . If a location update event does not occur in step  130 , the MS  100  jumps to step  134 . The MS receives a MOB_PAG-ADV message from the first BS  110  during a PLI in step  134 . Steps  136  to  140  are the same as steps  130  to  134  except that the preferred BS has changed to the second BS  120 . 
     As illustrated in  FIG. 1 , in the case where the preferred BS changes from the first BS  110  to the second BS  120 , an analysis of the occurrence of a location update event in step  136  reveals that the two BSs  110  and  120  are in the same paging group. Hence the MS jumps from step  136  to step  140  without a location update. 
       FIG. 2  is a diagram illustrating a signal flow for a conventional Zone Update process. 
     Referring to  FIG. 2 , when detecting a change in its paging group, the MS  200  transmits an initial ranging/dedicated ranging Code Division Multiple Access (CDMA) Code (M 20 ) to a preferred BS, herein the BS  220 , according to valid DCD and UCD information received from the BS  220 . 
     The BS  220  transmits Uplink BandWidth (UL BW) allocation information to the MS  200  by a RNG-RSP message with status=success (M 21 ) and a CDMA-Allocation-IE message (M 22 ) so that the MS  200  can transmit an uplink message. 
     The MS  200  transmits a RNG-REQ message with ranging purpose=0x02 (M 23 ) according to the UL BW allocation information. That is, the MS  200  sets Value of a Ranging Purpose Indication Type, Length, Value (TLV) to indicate a location update request in the RNG-REQ message with ranging purpose=0x02 (M 23 ). 
     The BS  220  replies with an RNG-RSP message with location update response (M 24 ), i.e. including a Location Update Response (LUR) TLV indicating success. The BS  220  may include paging information such as a new paging cycle, a new paging offset, and a new PG-ID in the RNG-RSP message with location update response (M 24 ). 
     Upon receipt of the RNG-RSP message with location update response (M 24 ), the MS  200  determines whether the location update is successful in step  202 . If the location update is successful, the MS  200  completes the location update process in step  204 . If the location update has failed, the MS  200  performs network entry initialization in step  206 . 
       FIG. 3  is a diagram illustrating a signal flow for a conventional process for processing pending downlink traffic transmission during the Zone Update. Steps ( 302 ˜ 306 ) or messages (M 20 ˜M 24 ) described with reference to  FIGS. 1 and 2  will not be described herein. 
     Referring to  FIG. 3 , when detecting the change of the preferred BS from a first BS  310  to a second BS  320  in a different paging group in an idle mode, i.e., when a location update event occurs, the MS  300  and the second BS  320  exchange M 20  to M 24  messages as illustrated in  FIG. 2 . Upon receipt of a RNG-RSP message with location update response (M 24 ), the MS  300  completes the location update in step  336 . 
     Upon receipt of the RNG-RSP message with location update response (M 24 ), the MS  300  also monitors a valid PLI from the second BS  320  using new paging information included in the RNG-RSP message with location update response (M 24 ). Hence, the MS  300  can receive a MOB_PAG-ADV message (M 30 ) indicating occurrence of downlink traffic in the valid PLI. 
     When detecting the presence of the downlink traffic, the MS  300  releases itself from the idle mode and performs network reentry in step  338 . 
     A network cannot be aware of a paging group of the MS  300  until the MS  300  completes the location update. In this case, if there is downlink traffic for the MS  300 , a downlink traffic transmission delay may occur due to the incapability of transmitting the downlink traffic to the MS  300 . The MS  300  cannot determine the occurrence of the downlink traffic until receiving the MOB_PAG-ADV message (M 30 ), despite the completion of the location update by the time of receiving the RNG-RSP message with location update response (M 24 ). 
     A shortcoming with the above conventional location update process is that the MS does not know whether downlink traffic exists for the MS even after a successful location update. The MS knows the occurrence of the downlink traffic only when an updated PLI comes. 
     SUMMARY OF THE INVENTION 
     An aspect of the present invention is to substantially solve at least the above problems and/or disadvantages and to provide at least the advantages below. Accordingly, an aspect of the present invention is to provide an apparatus and method for updating the location of an idle-mode MS such that the delay of downlink traffic transmission is decreased in a BWA communication system. 
     Another aspect of the present invention is to provide an apparatus and method for reducing the delay of downlink traffic transmission during a location update by an idle-mode MS in a BWA communication system. 
     A further aspect of the present invention is to provide an apparatus and method for transmitting a location update response message indicating whether there is pending downlink traffic transmission for an MS that has requested a location update in a BWA communication system. 
     According to one aspect of the present invention, a location updating method in a broadband wireless access communication system includes receiving a ranging request message requesting a location update from an MS in idle mode, when a location update condition is met, determining whether downlink traffic exists for the MS, if the downlink traffic exists for the MS, generating a ranging response message including information indicating that there is downlink traffic pending for the MS and transmitting the ranging response message to the MS. 
     According to another aspect of the present invention, a method of an MS in idle mode for performing a location update in a broadband wireless access communication system includes transmitting a ranging request message requesting location update to a BS when a location update condition is met in an idle mode, and receiving a ranging response message including information for location update response from the BS, wherein the information indicates whether downlink traffic is pending for the MS. 
     According to yet another aspect of the present invention, a BS in a broadband wireless access communication system includes a transceiver for processing a Radio Frequency (RF) signal and baseband signal for communicating with an MS, a processing unit configured to perform a location update procedure when a ranging request message is received from an MS in the idle mode requesting location update, wherein the location update procedure includes determining whether downlink traffic exists for the MS, and generating a ranging response message including information indicating whether the downlink traffic is pending for the MS. 
     According to still another aspect of the present invention, an MS in a broadband wireless access communication system includes a transceiver for processing an RF signal and baseband signal for communicating with a BS and a processing unit configured to generate a ranging request message for requesting a location update when a location update condition is met in the idle mode, and to process a ranging response message received from the BS in response to the ranging request message to update the location, wherein the ranging response message includes information indicating whether there is downlink traffic pending for the MS. 
     According to still another aspect of the present invention, a broadband wireless access communication system includes at least one BS for receiving a ranging request message requesting location update from an MS in the idle mode when a location update condition is met, determining whether downlink traffic exists for the MS, generating a ranging response message including information indicating that there is downlink traffic pending for the MS if the downlink traffic exists for the MS, and transmitting the ranging response message to the MS and at least one MS for transmitting a ranging request message requesting location update to a BS when a location update condition is met in the idle mode, and receiving a ranging response message including information for a location update response from the BS, the information indicating whether the downlink traffic is pending. 
    
    
     
       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 flowchart illustrating a conventional location update process when a preferred BS is changed within the same paging group; 
         FIG. 2  is a diagram illustrating a signal flow for a conventional Zone Update process; 
         FIG. 3  is a diagram illustrating a signal flow for a conventional process for processing pending downlink traffic transmission during the Zone Update; 
         FIG. 4  is a diagram illustrating a signal flow for a process for processing pending downlink traffic transmission during a Zone Update in a BWA communication system according to the present invention; 
         FIG. 5  is a block diagram of a BS in the BWA communication system according to the present invention; and 
         FIG. 6  is a block diagram of an MS in the BWA communication system according to the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Preferred embodiments 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. 
     The present invention provides an apparatus and method for updating the location of an idle-mode MS so as to reduce the delay of downlink traffic directed to the MS, in particular to overcome the problem encountered with the present IEEE 802.16e standard in that an MS is not aware of the presence of downlink traffic until an updated PLI, in a BWA communication system. 
       FIG. 4  is a diagram illustrating a signal flow for a process for processing pending downlink traffic transmission during a Zone Update in a BWA communication system according to the present invention. A description of steps ( 402 ˜ 406 ) or messages (M 20 ˜M 23 ) described earlier with reference to  FIGS. 1 ,  2  and  3  is not provided herein. 
     Referring to  FIG. 4 , when an MS  400  detects in an idle mode that a preferred BS has changed from a first BS  410  to a second BS  420  in a different paging group in step  432 , the MS  400  transmits an initial ranging/dedicated ranging CDMA Code (M 20 ) to the second BS  420 . The BS  420  transmits a RNG-RSP message with status=success (M 21 ) and a CDMA-Allocation-IE message (M 22 ) to the MS  400 . Then the MS  400  transmits a RNG-REQ message with ranging purpose=0x02 (M 23 ) to the second BS  420 . 
     Hereafter, the second BS  420  determines that there is downlink traffic pending transmission for the MS  400  in step  434  and the second BS  420  transmits a RNG-RSP message with location update response (M 40 ) to the MS  400 . The RNG-RSP message with location update response (M 40 ) contains new paging information and information indicating the presence of the downlink traffic. 
     As the MS  400  is aware of the pending downlink traffic transmission by the RNG-RSP message with location update response (M 40 ), it completes the location update process and performs network reentry from the idle mode in step  436 . 
     The RNG-RSP message with location update response (M 40 ) includes an LUR TLV configured as shown in Table 1 below. 
     
       
         
               
               
               
               
             
               
               
               
               
             
           
               
                   
                 TABLE 1 
               
               
                   
                   
               
               
                   
                 Type 
                 Length 
                 Value 
               
               
                   
                   
               
             
             
               
                   
               
             
          
           
               
                 LUR 
                 23 
                 1 
                 0x00 = Failure of Location Update. The MS shall 
               
               
                   
                   
                   
                 perform Network Reentry from Idle Mode 
               
               
                   
                   
                   
                 0x01 = Success of Location Update 
               
               
                   
                   
                   
                 0x02 = Success of Location Update and presence 
               
               
                   
                   
                   
                 of DL traffic pending 
               
               
                   
                   
                   
                 0x03~0xFF = Reserved 
               
               
                   
               
             
          
         
       
     
     In Table 1, the TLV values other than a Value of 0x02 are in compliance with the IEEE 802.16e-2005 standard. 
       FIG. 5  is a block diagram of a BS in the BWA communication system according to the present invention. Referring to  FIG. 5 , the BS includes a controller  500 , an interface module  502 , a RNG-REQ processing unit  504 , a RNG-RSP processing unit  506 , and a downlink traffic processing unit  508 . 
     The interface module  502  is a module for communicating with an MS, including a Radio Frequency (RF) processing unit and a baseband processing unit. The RF processing unit downconverts an RF signal received through an antenna to a baseband signal and provides the baseband signal to the baseband processing unit. It also upconverts a baseband signal received from the baseband processing unit to an RF signal transmittable over air and transmits the RF signal through the antenna. In BWA, for example, the baseband processing unit processes an RF signal received from the RF processing unit by Fast Fourier Transform (FFT) and channel decoding and provides the original information data to the controller  500 . In the reverse order, the baseband processing unit processes data received from the controller  500  by channel encoding and Inverse Fast Fourier Transform (IFFT) and provides the processed data to the RF processing unit. 
     The RNG-REQ processing unit  504  processes a RNG-REQ message with ranging purpose=0x02 (M 23 ) received from the idle-mode MS  400 . It identifies whether the ranging purpose of the RNG-REQ message with ranging purpose=0x02 (M 23 ) is for location update, initial ranging, or network entry and operates correspondingly. If the RNG-REQ message with ranging purpose=0x02 (M 23 ) includes the ID of the MS  400  and Ranging Purpose Indication Bit#1=1, the RNG-REQ processing unit  504  considers that the RNG-REQ message with ranging purpose=0x02 (M 23 ) requests a location update. 
     The downlink traffic processing unit  508  operates after the location update requested by the MS  400  is performed. If the location update is successful, the downlink traffic processing unit  508  monitors occurrence of downlink traffic for the MS  400  and provides the monitoring result to the RNG-RSP processing unit  506 . 
     The RNG-RSP processing unit  506  generates a RNG-RSP message with location update response (M 40 ) with an LUR TLV parameter configured as shown in Table 1 according to whether the location update is successful and whether there is pending downlink traffic transmission from operations of the RNG-REQ processing unit  504  and the downlink traffic processing unit  508 . 
     The controller  500  controls the interface module  502 , the RNG-REQ processing unit  504 , the RNG-RSP processing unit  506 , and the downlink traffic processing unit  508 . That is, the controller  500  can implement the functionalities of the interface module  502 , the RNG-REQ processing unit  504 , the RNG-RSP processing unit  506 , and the downlink traffic processing unit  508 . While the interface module  502 , the RNG-REQ processing unit  504 , the RNG-RSP processing unit  506 , and the downlink traffic processing unit  508  are shown separately for illustrative purposes, all or part of them may be incorporated into the controller  500  in real implementation. 
       FIG. 6  is a block diagram of an MS in the BWA communication system according to the present invention. Referring to  FIG. 6 , the MS includes a controller  600 , an interface module  602 , a RNG-REQ processing unit  604 , a RNG-RSP processing unit  606 , a location update processing unit  608 , and a network reentry processing unit  610 . 
     The interface module  602  is a module for communicating with the BS, including an RF processing unit and a baseband processing unit. The RF processing unit downconverts an RF signal received through an antenna to a baseband signal and provides the baseband signal to the baseband processing unit. It also upconverts a baseband signal received from the baseband processing unit to an RF signal transmittable over air and transmits the RF signal through the antenna. In BWA, for example, the baseband processing unit processes an RF signal received from the RF processing unit by FFT and channel decoding and provides the original information data to the controller  600 . In the reverse order, the baseband processing unit processes data received from the controller  600  by channel encoding and IFFT and provides the processed data to the RF processing unit. 
     The RNG-REQ processing unit  604  generates a RNG-REQ message with ranging purpose=0x02 (M 23 ) for a location update when any of location update conditions is met in an idle mode. The RNG-REQ message with ranging purpose=0x02 (M 23 ), having the_ranging purpose of location update includes the ID of the MS (herein, the MS  400 ) and Ranging Purpose Indication Bit#1=1. 
     The RNG-RSP processing unit  606  processes a RNG-RSP message with location update response (M 40 ) received from the BS  420  to perform location update for the MS  400  in the idle mode. The RNG-RSP processing unit  606  provides location update information according to an LUR TLV value to the location update processing unit  608  and informs the network reentry processing unit  610  whether there is pending downlink traffic transmission according to the LUR TLV value. Herein, the location update information can be new paging information with a new paging cycle, a new paging offset, and a new PG ID. 
     The location update processing unit  608  updates a PLI using the new paging cycle and the new paging offset, and stores the new PG-ID according to the new paging information provided from the RNG-RSP processing unit  606 . 
     The network reentry processing unit  610  attempts network reentry to the BS  420 , being the preferred BS, when the RNG-RSP processing unit  606  indicates that there is pending downlink traffic transmission. 
     The controller  600  controls the interface module  602 , the RNG-REQ processing unit  604 , the RNG-RSP processing unit  606 , the location update processing unit  608 , and the network reentry processing unit  610 . That is, the controller  600  can implement the functionalities of the interface module  602 , the RNG-REQ processing unit  604 , the RNG-RSP processing unit  606 , the location update processing unit  608 , and the network reentry processing unit  610 . While the interface module  602 , the RNG-REQ processing unit  604 , the RNG-RSP processing unit  606 , the location update processing unit  608 , and the network reentry processing unit  610  are shown separately for illustrative purposes, all or part of them may be incorporated into the controller  600  in real implementation. 
     As described above, the present invention provides a location updating apparatus and method in which a BS determines the presence or absence of downlink traffic for an MS and transmits a RNG-RSP message indicating the presence or absence of downlink traffic to the MS during a location update of the MS in an idle mode. Therefore, the delay of downlink traffic transmission is reduced without using additional resources during the location update. 
     While the invention has been shown and described with reference to certain preferred 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.