Patent Document

PRIORITY 
     This application claims priority under 35 U.S.C. §119(a) to a Korean Patent Application filed in the Korean Intellectual Property Office on Jun. 30, 2008 and assigned Serial No. 10-2008-0062517, the contents of which are herein incorporated by reference. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a method and device for controlling handover message transmission power in a mobile communication system. More particularly, the present invention relates to a method and device for controlling transmission power of a handover ranging message considering uplink of a mobile station. 
     2. Description of the Related Art 
     In general, a mobile communication system supports handover for establishing a new communication path between a Mobile Station (hereinafter, referred to as “MS”) and a Base Station (hereinafter, referred to as “BS”) according to the change of the communication environment in order to support a seamless service. 
     As illustrated in  FIG. 1 , for the handover, the IEEE 802.16e mobile WiMAX system performs a scanning procedure (not shown) in which an MS measures signals of a serving BS and a neighbor BS, a pre-handover procedure  110  of determining a handover target BS of the MS, and a handover execution procedure  120  in which the MS resets connection with the target BS. That is, every predetermined period or whenever a received signal quality of the serving BS decreases below a predetermined level, the MS transmits a scanning request to the serving BS and acquires signal quality information of neighbor BSs. If the handover target BS is determined by the serving BS, the MS performs handover ranging for doing handover to the target BS after releasing connection with the serving BS. Here, a ranging process between the target BS and the MS gets different depending on whether an association procedure of adjusting an initial MS power value, a time difference value for synchronization, etc. with the target BS of the MS has been previously performed. 
     In case that the association procedure has not been previously performed, the MS selects a random ranging code from a CDMA handover ranging domain of the target BS and transmits this within a ranging interval of the target BS. At this time, if the target BS successfully receives the ranging code, the target BS transmits a ranging response (RNG_RSP) message representing a success to the MS, thereby providing uplink allocation for a ranging request (RNG_REQ) message. Or, in case that the target BS has received the ranging code but cannot use the received ranging code, the target BS transmits the MS a ranging response (RNG_RSP) message set to ‘continue’ and allows the MS to transmit a different random ranging code within a ranging interval of a next period. In case that the serving BS fails to receive the ranging code, the MS retransmits a ranging code after a predetermined time (T 3 ) lapses. 
     On the contrary, in case that the association procedure has been previously performed, the serving BS transmits a Fast_ranging_IE( ) to the MS and informs of ranging code and slot information to be used in a ranging request (RNG-REQ), and the MS transmits a ranging request (RNG-REQ) message at a defined slot using the ranging code. 
     When performing handover ranging as above, the conventional art determines the maximum transmission power of the handover ranging message using downlink information as in Equation 1 below and then, transmits the ranging code or ranging request message at a power level below the determined maximum transmission power. Here, the maximum transmission power is a value determined on the presupposition that channel situations of uplink and downlink are symmetric.
 
 P   TX   _   IR   _   MAX =EIR xP   IR,max   −BS _EIRP−RSS  (1)
 
     Here, the ‘T TX   _   IR   _   MAX ’ represents the maximum transmission power for a ranging message, the ‘EIRxP IR,max ’ represents the maximum equivalent isotropic received power at BS, the ‘BS_EIRP’ represents equivalent isotropic radiated power of BS, and the ‘RSS’ represents an RSSI (Received Signal Strength Indicator) measured by an MS. 
     However, in an actual OFDMA (Orthogonal Frequency Division Multiple Access) system, a difference of interference between uplink and downlink may lead to the occurrence of asymmetric channel situations of the uplink and downlink. Accordingly, in case that it is to transmit a handover ranging message at the maximum transmission power considering only downlink as in Equation 1 above, because of the bad channel situation of the uplink, a BS may fail to successfully receive the handover ranging message. In case that the MS fails to successfully receive the ranging code as above, after the MS increases transmission power by one level and waits a response during a predetermined time (T 3 ), the MS selects and retransmits a different ranging code. This causes an increase of a handover interruption time and, resultantly, there is a problem that a quality of a service is deteriorated. If initial transmission power is greatly set to solve the above problem, the power consumption of the MS can increase and act as great interference in a BS, thus leading to the deterioration of performance of the entire system. 
     Accordingly, there is a need to provide a method for controlling the maximum transmission power for handover ranging in an asymmetric situation of the uplink and downlink channels. 
     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, one aspect of the present invention is to provide a method and device for controlling handover message transmission power in a mobile communication system. 
     Another aspect of the present invention is to provide a method and device for controlling handover message transmission power considering uplink of an MS in a mobile communication system. 
     A further aspect of the present invention is to provide a method and device for controlling handover message transmission power, for reducing a handover interruption time in a mobile communication system. 
     The above aspects are achieved by providing a method and device for controlling handover message transmission power in a mobile communication system. 
     According to one aspect of the present invention, a method for controlling handover message transmission power of a mobile station in a mobile communication system is provided. The method includes acquiring uplink information on a handover target base station, determining the maximum transmission power of a handover ranging message using the uplink information, and transmitting the handover target base station a handover ranging message having a power level below the determined maximum transmission power. 
     According to another aspect of the present invention, a method of a serving base station for controlling handover message transmission power of a mobile station in a mobile communication system is provided. The method includes the steps of, if a scanning interval allocation request (MOB_SCN_REQ) message is received from a mobile station, providing information on an uplink and downlink measurement interval to the mobile station and neighbor base stations, receiving uplink information from the neighbor base stations, when handover initiation is requested from the mobile station, determining a handover target base station among the neighbor base stations, and transmitting uplink information received from the handover target base station to the mobile station. 
     According to a further aspect of the present invention, a method of a neighbor base station for controlling handover message transmission power of a mobile station in a mobile communication system is provided. The method includes the steps of measuring an uplink signal of a specific mobile station using information on an uplink measurement interval provided from a serving base station of the specific mobile station, providing the uplink signal measurement result to a mobile station, and providing received power information on a handover ranging message to the mobile station. 
     According to a yet another aspect of the present invention, a device for controlling handover message transmission power of a mobile station in a mobile communication system is provided. The device includes a transceiver for receiving uplink information on a handover target base station, and transmitting the handover target base station a handover ranging message, a transmission power determiner for determining the maximum transmission power of a handover ranging message using the uplink information, and a transmission power controller for controlling the handover ranging message to be transmitted at a power level below the determined maximum transmission power. 
     According to a still another aspect of the present invention, a device of a serving base station for controlling handover message transmission power of a mobile station in a mobile communication system is provided. The device includes a controller for, if a scanning interval allocation request (MOB_SCN_REQ) message is received from a mobile station, providing information on an uplink and downlink measurement interval to the mobile station and neighbor base stations, and transmitting uplink information received from the neighbor base stations to the mobile station. 
     Other aspects, advantages, and salient features of the invention will become apparent to those skilled in the art from the following detailed description, which, taken in conjunction with the annexed drawings, discloses exemplary embodiments of the invention 
    
    
     
       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 handover procedure of the IEEE 802.16e mobile WiMAX system; 
         FIG. 2  is a diagram illustrating a procedure for acquiring uplink information upon handover execution in a mobile communication system according to the present invention; 
         FIG. 3  is a diagram illustrating a procedure of performing handover using the maximum transmission power considering uplink in a mobile communication system according to the present invention; 
         FIG. 4  is a diagram illustrating an operation procedure of an MS determining the maximum transmission power of a handover message considering uplink in a mobile communication system according to an exemplary embodiment of the present invention; 
         FIG. 5  is a diagram illustrating an operation procedure of a serving BS in a mobile communication system according to an exemplary embodiment of the present invention; 
         FIG. 6  is a diagram illustrating an operation procedure of a neighbor BS in a mobile communication system according to an exemplary embodiment of the present invention; 
         FIG. 7  is a block diagram illustrating a construction of an MS in a mobile communication system according to an exemplary embodiment of the present invention; 
         FIG. 8  is a block diagram illustrating a construction of a BS in a mobile communication system according to an exemplary embodiment of the present invention; 
         FIG. 9  is a diagram illustrating a service disruption time at execution of handover on the basis of the maximum transmission power according to the conventional art and the present invention; and 
         FIG. 10  is a diagram illustrating a handover up message success and failure rate at execution of handover on the basis of the maximum transmission power according to the conventional art and 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 
     The following description with reference to the accompanying drawings is provided to assist in a comprehensive understanding of exemplary embodiments of the invention as defined by the claims and their equivalents. It includes various specific details to assist in that understanding but these are to be regarded as merely exemplary. Accordingly, those of ordinary skill in the art will recognize that various changes and modifications of the embodiments described herein can be made without departing from the scope and spirit of the invention. Also, descriptions of well-known functions and constructions are omitted for clarity and conciseness. 
     The terms and words used in the following description and claims are not limited to the bibliographical meanings, but, are merely used by the inventor to enable a clear and consistent understanding of the invention. Accordingly, it should be apparent to those skilled in the art that the following description of exemplary embodiments of the present invention are provided for illustration purpose only and not for the purpose of limiting the invention as defined by the appended claims and their equivalents. 
     It is to be understood that the singular forms “a,” “an,” and “the” include plural referents unless the context clearly dictates otherwise. Thus, for example, reference to “a component surface” includes reference to one or more of such surfaces. 
     A technology for determining the maximum transmission power of a handover message considering uplink of an MS in a mobile communication system according to the present invention is described below. That is, the following description is made for a method and device in which neighbor BSs measure an uplink signal of an MS in a scanning process, and the MS determines the maximum transmission power of a handover ranging message using measured uplink information and then transmits a handover ranging message having a power level below the determined maximum transmission power to a handover target BS. 
     Then, a description is first made for a method for acquiring uplink information for determining the maximum transmission power of a handover ranging message. 
       FIG. 2  illustrates a procedure for acquiring uplink information upon handover execution in a mobile communication system according to the present invention. 
     Referring to  FIG. 2 , first, every preset period or if a downlink signal is attenuated, in step  210 , an MS  200  transmits a scanning interval allocation request (MOB_SCN_REQ) message to a serving BS  202 . After that, in step  212 , the serving BS  202  transmits neighbor BSs  204  and  206  a neighbor BS scanning request (NBR_SCN_REQ) message including information of the MS  200  and information on an uplink measurement interval. In step  214 , the serving BS  202  transmits the MS  200  a scanning interval allocation response (MOB_SCN_RSP) message including information on an interval capable of measuring downlink of the neighbor BSs. 
     After that, in step  216 , the MS  200  and the neighbor BSs  204  and  206  perform synchronization for a scanning process and measures uplink and downlink signals. That is, the MS  200  measures a downlink signal of each of the neighbor BSs  204  and  206  in the downlink measurement interval and measures signal power, interference power, noise power and the like, and the neighbor BSs  204  and  206  each measure an uplink signal of the MS  200  in the uplink measurement interval and measures signal power, interference power, noise power and the like. Here, the MS  200  transmits a scanning message to the neighbor BSs  204  and  206  for the sake of the scanning process, and stores a transmission power value of the scanning message. 
     After that, in step  218 , the neighbor BSs  204  and  206  each transmit a neighbor BS scanning response (NBR_SCN_RSP) message including the uplink signal measurement result to the serving BS  202 . 
     If a downlink signal of a serving BS is attenuated, in step  230 , the MS  200  transmits a handover request (MOB_MSHO_REQ) message to the serving BS  202  and initiates handover. Here, although the MS  200  has requested handover, the serving BS  202  may initiate the handover by sensing that an uplink signal is attenuated below a predetermined level and transmitting a handover request (MOB_BSHO_REQ) message to the MS. 
     In step  232 , the serving BS  202  receiving a handover initiation request from the MS  200  or attempting handover transmits a handover previous notification (HO-pre-notification) message to the neighbor BSs  204  and  206 . Here, the handover previous notification message includes information of required QoS, bandwidth, and the like. 
     Then, in step  234 , the neighbor BSs  204  and  206  transmit a handover previous notification response (HO-pre-notification response) message to the serving BS  202 . At this time, the handover previous notification response message includes a service quality level capable of being provided in each of the neighbor BSs  204  and  206  and average equivalent isotropic received power for handover ranging message (EIR X P HR,average ). At this time, the average equivalent isotropic received power for the handover ranging message represents average equivalent isotropic received power for handover ranging message that the neighbor BSs  204  and  206  each receive from a plurality of MSs. That is, the neighbor BSs  204  and  206  each measure equivalent isotropic received power for handover ranging message received whenever the handover ranging message are received from the plurality of MSs, determine an average value with reference to values of equivalent isotropic received power for previously received handover ranging message and store, and then provide to the serving BS  202  through the handover previous notification response message. 
     After that, the serving BS  202  selects one neighbor BS capable of providing better service to the MS, for example, a 1st neighbor BS  204  among the neighbor BSs  204  and  206  and determines as a handover target BS and then, proceeds to step  236  and transmits a handover confirm (HO-confirm) message to the 1st neighbor BS  204  determined as the handover target BS. 
     And, in step  238 , the serving BS  202  transmits the MS  200  a handover response (MOB_BSHO_RSP) message of indicating a handover to the 1st neighbor BS  204  that is the handover target BS. Here, the handover response message includes ID information of the 1st neighbor BS  204 , uplink measurement information (e.g., power of an uplink received signal, interference power, and noise power) acquired from the neighbor BS  204  in the scanning process, and average equivalent isotropic received power for handover ranging message acquired through the handover previous notification response message. 
     After that, in step  240 , the MS  200  transmits the serving BS  202  a handover indication (MOB_HO_IND) message as final indication for handover execution, so a channel between the MS and the serving BS is released in step  242 . 
     In  FIG. 2  aforementioned, the neighbor BS obtains average equivalent isotropic received power for handover ranging message received from a plurality of MSs and provides to the serving BS, but may obtain the maximum equivalent isotropic received power or the minimum equivalent isotropic received power among equivalent isotropic received power for the handover ranging message received from the plurality of MSs in place of the average equivalent isotropic received power and provide to the serving BS. Also, uplink information measured in the neighbor BS may be forwarded to an MS through a backbone network, and the neighbor BS may forward directly to the MS through a wireless link. 
     Then, a description is made for a method for determining the maximum transmission power of the handover ranging message through the uplink information acquired as in  FIG. 2  above, and performing handover ranging on the basis of this. 
       FIG. 3  illustrates a procedure of performing handover using the maximum transmission power considering uplink in a mobile communication system according to the present invention. 
     Referring to  FIG. 3 , in step  310 , an MS  300  transmits a handover indication (MOB_HO_IND) message to a serving BS  302 . If a channel with the serving BS  302  is released through step  312 , the MS  300  proceeds to step  314  and performs synchronization with a handover target BS  304 . 
     After that, after determining the maximum transmission power of a handover ranging message as in Equation 2 or Equation 3 below using previously acquired uplink information, the MS  300  proceeds to step  316  and transmits a CDMA_Ranging_Code to the target BS  304  at a power level below the determined maximum transmission power. Then, in step  318 , the target BS  304  transmits a ranging response message or a CDMA_allocation_IE( ) message to the MS  300 . 
     Equation 2 below represents a method of determining the maximum transmission power using uplink received signal strength, and Equation 3 below represents a method of determining the maximum transmission power considering uplink received signal strength and uplink interference.
 
 P   TX   _   HR   _   MAX =EIR xP   HR,max,min,average   −MS _EIRP−RSS BS   (2)
 
 P   TX   _   HR   _   MAX =EIR xP   HR,max,min,average   −MS _EIRP−10 log(RSS BS /10 −P   interference   −P   noise )  (3)
 
     In Equation 2 and Equation 3, the T TX   _   HR   _   MAX  represents the maximum transmission power of a handover ranging message, the ‘EIRxP HR,max,min,average ’ represents an average value, maximum value, or minimum value of equivalent isotropic received power for handover ranging message, and is a value determined and received in a neighbor BS determined as a handover target BS. Also, the ‘MS_EIRP’ represents equivalent isotrop radiated power of MS, and uses a transmission power value of a scanning message that the MS transmits in a scanning process. And, the ‘RSS BS ’ represents an RSSI (Received Signal Strength Indicator) measured in the target BS, and the ‘P interference ’ and the ‘P noise ’ represent interference power of a linear unit for uplink measured in the target BS and noise power. 
     After that, in step  320 , the MS  300  transmits the target BS  304  a ranging request (RNG_REQ) message for initial power leveling and range measurement. After transmitting the MS  300  a ranging response (RNG_RSP) message including information on power adjustment in step  322 , the target BS  304  completes a network entry process between the MS  300  and the target BS  304  through step  324 . 
       FIG. 4  illustrates an operation procedure of an MS determining the maximum transmission power of a handover message considering uplink in a mobile communication system according to an exemplary embodiment of the present invention. 
     Referring to  FIG. 4 , every preset period or if it is sensed that downlink signal power is attenuated below a predetermined level in step  401 , the MS proceeds to step  403  and transmits a scanning interval allocation request (MOB_SCN_REQ) message to a serving BS for scanning. 
     After that, in step  405 , the MS receives a scanning interval allocation response (MOB_SCN_RSP) message from the serving BS and acquires information on downlink measurement intervals of neighbor BSs and then, in step  407 , performs synchronization with the neighbor BSs and measures a downlink signal. At this time, the MS transmits a scanning message to the neighbor BSs and stores a transmission power value of the scanning message. 
     Next, in step  409 , the MS senses if downlink signal power of the serving BS is attenuated below a predetermined level and, when it is attenuated, proceeds to step  411  and transmits a handover request (MOB_MSHO_REQ) message to the serving BS  202  and requests handover initiation and then, proceeds to step  415  below. On the contrary, when the downlink signal power is not attenuated below a predetermined level, the MS proceeds to step  413  and checks if a handover request (MOB_BSHO_REQ) message for handover initiation is received from the serving BS and, when the handover request message is not received, returns to step  409  and again performs subsequent steps and, when the handover request message is received, proceeds to step  415  below. 
     In step  415 , the MS receives a handover response (MOB_BSHO_RSP) message including information of a handover target BS from the serving BS. Here, the handover response message includes ID information of the target BS, information that the target BS measures on uplink of the MS, and average equivalent isotropic received power for handover ranging message measured in the target BS. After that, in step  417 , the MS transmits a handover indication (MOB_HO_IND) message to the serving BS and releases a channel with the serving BS. 
     After that, in step  419 , the MS determines the maximum transmission power as in Equation 2 or Equation 3 using the received uplink information of the target BS and the average equivalent isotropic received power for the handover ranging message. 
     Next, in step  421 , the MS transmits the CDMA ranging code or ranging request message at a level below the determined maximum transmission power and performs a network entry process. 
     After that, the MS terminates the algorithm according to the present invention. 
       FIG. 5  illustrates an operation procedure of a serving BS in a mobile communication system according to an exemplary embodiment of the present invention. 
     Referring to  FIG. 5 , if a scanning interval allocation request (MOB_SCN_REQ) message is received from an MS in step  501 , in step  503 , the serving BS transmits neighbor BSs a neighbor BS scanning request (NBR_SCN_REQ) message including information of the MS and information on an uplink measurement interval, and transmits the MS a scanning interval allocation response (MOB_SCN_RSP) message including information on an interval capable of measuring downlink of neighbor BSs. 
     After that, in step  505 , the serving BS receives a neighbor BS scanning response (NBR_SCN_REQ) message including the uplink signal measurement result of the MS from the neighbor BSs. At this time, the uplink signal measurement result includes an uplink received signal power level, an interference power level, a noise power level, and the like. 
     After that, in step  507 , the serving BS monitors if uplink signal power of the MS is attenuated below a predetermined level and, when it is attenuated, the serving BS proceeds to step  509  and transmits a handover request (MOB_BSHO_REQ) message to the MS and requests handover initiation and then, the serving BS proceeds to step  513  below. On the contrary, when the uplink signal power is not attenuated below a predetermined level, the serving BS proceeds to step  511  and checks if a handover request (MOB_MSHO_REQ) message for handover initiation is received from the MS and, when the handover request (MOB_MSHO_REQ) message is not received, the serving BS returns to step  507  and again performs subsequent steps and, when the handover request (MOB_MSHO_REQ) message is received, the serving BS proceeds to step  513  below. 
     After that, in step  513 , the serving BS transmits a handover previous notification (HO-pre-notification) message to the neighbor BSs. Here, the handover previous notification message includes information of required QoS, bandwidth, etc. 
     After that, in step  515 , the serving BS receives, from the neighbor BSs, a handover previous notification response (HO-pre-notification response) message including a service quality level capable of being provided by each and average equivalent isotropic received power for handover ranging message. 
     After that, in step  517 , the serving BS selects a neighbor BS capable of providing a better service to the MS among the neighbor BSs and determines as a handover target BS, and transmits a handover confirm (HO-confirm) message to the handover target BS. 
     After that, in step  519 , the serving BS transmits the MS a handover response (MOB_BSHO_RSP) message indicating a handover to the handover target BS. Here, the handover response message includes ID information of the target BS, uplink information that the target BS measures in the scanning process, and average equivalent isotropic received power for handover ranging message of the target BS. 
     After that, in step  521 , the serving BS receives a handover indication (MOB_HO_IND) message from the MS and releases a channel with the MS and, terminates the algorithm according to the present invention. 
       FIG. 6  illustrates an operation procedure of a neighbor BS in a mobile communication system according to an exemplary embodiment of the present invention. 
     Referring to  FIG. 6 , in step  601 , the neighbor BS checks if a neighbor BS scanning request (NBR_SCN_REQ) message including information of a specific MS and information on an uplink measurement interval from a serving BS of the specific MS. When the neighbor BS scanning request (NBR_SCN_REQ) message is received, in step  603 , the neighbor BS measures a signal power level, an interference power level, and a noise power level, and the like from an uplink signal of the specific MS in the uplink measurement interval and then, the neighbor BS proceeds to step  605  and transmits the serving BS a neighbor BS scanning response (NBR_SCN_REQ) message including the uplink signal measurement result. 
     After that, in step  607 , the neighbor BS checks if a handover previous notification (HO-pre-notification) message is received from the serving BS. Here, the handover previous notification message includes information on required QoS, bandwidth, etc. 
     When the handover previous notification (HO-pre-notification) message is received, in step  609 , the neighbor BS transmits the serving BS a handover previous notification response (HO-pre-notification response) message including a service quality level that itself can provide and average equivalent isotropic received power for handover ranging message. 
     After that, the neighbor BS receives a handover confirm (HO-confirm) message of informing that it is determined as a handover target BS from the serving BS and performs synchronization with the MS and then, in step  611 , the neighbor BS receives a CDMA_Ranging_Code or a ranging request (RNG-REQ) message from the MS and transmits a response message to this, thereby performing a network entry process. Here, the CDMA_Ranging_Code or ranging request (RNG_REQ) message received from the MS has a level below the maximum transmission power determined considering uplink in the MS. 
     After that, in step  613 , the neighbor BS updates average equivalent isotropic received power for handover ranging message using power of the received CDMA_Ranging_Code or ranging request (RNG_REQ) message, and terminates the algorithm according to the present invention. 
       FIG. 7  illustrates a construction of an MS in a mobile communication system according to an exemplary embodiment of the present invention. 
     As illustrated in  FIG. 7 , the MS includes a transceiver  700 , a message generation and analysis unit  710 , a controller  720 , and a storage unit  730 . The controller  720  includes a transmission power determiner  724  and a transmission power controller  722 . 
     The transceiver  700  converts a signal received through an antenna into a baseband signal and provides to the message generation and analysis unit  710  and, according to the control of the controller  720 , converts a signal provided from the message generation and analysis unit  710  into a radio frequency signal and transmits to a serving BS or a neighbor BS through the antenna. 
     The message generation and analysis unit  710  analyzes a message provided from the transceiver  700  and provides to the controller  720  and, according to the control of the controller  720 , generates messages for scanning, previous handover, and handover execution and provides to the transceiver  700 . 
     The controller  720  processes and controls a general operation of the MS and, according to the present invention, controls and processes a function for determining the maximum transmission power of a handover ranging message considering uplink through the transmission power determiner  724  and transmitting a handover ranging message at a level below the determined maximum transmission power through the transmission power controller  722 . That is, the transmission power determiner  722  determines the maximum transmission power as in Equation 2 or Equation 3 above using uplink information on a handover target BS acquired from a serving BS through the transceiver  700  and average equivalent isotropic received power for handover ranging message. And, when transmitting a handover ranging message to a handover target BS through the transceiver  700 , the transmission power controller  722  controls the transceiver  700  such that the handover ranging message is sent at a power level below the determined maximum transmission power. Also, the controller  720  controls and processes a function for transmitting a scanning message to neighbor BSs for scanning, and storing transmission power of the scanning message in the storage unit  730 . 
     The storage unit  730  stores a program for a general operation of the MS and various kinds of data and, according to the control of the controller  720 , stores transmission power of a scanning message. 
       FIG. 8  illustrates a construction of a BS in a mobile communication system according to an exemplary embodiment of the present invention. 
     As illustrated in  FIG. 8 , the BS includes a transceiver  800 , a message generation and analysis unit  810 , a controller  820 , an uplink measurement unit  830 , and a storage unit  840 . 
     The transceiver  800  converts a signal received through an antenna into a baseband signal and provides to the message generation and analysis unit  810 , and converts a signal provided from the message generation and analysis unit  810  into a baseband signal and transmits to an MS or a neighbor BS through the antenna. 
     The message generation and analysis unit  810  analyzes a message provided from the transceiver  800  and provides to the controller  820  and, according to the control of the controller  820 , generates messages for scanning, previous handover, and handover execution and provides to the transceiver  800 . 
     The controller  820  process and controls a general operation of the BS and, particularly, when scanning is requested from an MS according to the present invention, controls and processes a function for providing downlink and uplink measurement interval information to the MS and neighbor BS and acquiring uplink measurement information from the neighbor BSs. Also, the controller  820  controls and processes a function for, when handover initiation is requested from the MS or it is judged that handover initiation is necessary due to the attenuation of an uplink signal, transmitting/receiving a handover previous notification message and a handover previous notification response message with the neighbor BSs and determining a handover target BS of the MS, and transmitting ID of the target BS, uplink measurement information, and average equivalent isotropic received power information for handover ranging message to the MS and requesting handover. 
     Also, the controller  820  controls and processes a function for receiving an uplink measurement interval of a specific MS from a serving BS of the specific MS, performing synchronization with a corresponding MS, measuring an uplink signal in a scanning interval through the uplink measurement unit  830 , and transmitting uplink measurement information to the serving BS. Also, the controller  820  controls and processes a function for, when a handover previous notification message is received from the serving BS, transmitting average equivalent isotropic received power or maximum/minimum equivalent isotropic received power for handover ranging message stored in the storage unit  840 , to the serving BS. And, the controller  820  controls and processes a function for, when a handover ranging message is received from the MS, controlling the uplink measurement unit  830  and updating average equivalent isotropic received power or maximum/minimum average equivalent isotropic received power for handover ranging message. 
     The uplink measurement unit  830  measures power of a signal received through the transceiver  800 . Particularly, the uplink measurement unit  830  measures an uplink signal received power level of the MS, an interference power level, a noise power level, and the like in an uplink scanning interval of a specific MS according to the control of the controller  820 . Also, the uplink measurement unit  830  measures equivalent isotropic received power for handover ranging message received from a plurality of MSs according to the control of the controller  820 , determines an average value or determines the maximum value or the minimum value, and provides to the controller  820 . 
     The storage unit  840  stores a program for a general operation of the BS and various kinds of data and, according to the control of the controller  820 , stores average equivalent isotropic received power or maximum/minimum equivalent isotropic received power for handover ranging message determined in the uplink measurement unit  830 . 
       FIG. 9  and  FIG. 10  illustrate a service disruption time cumulative distribution and the number of handover up message success and failure according to the conventional art and the present invention. Here, a horizontal axis of  FIG. 9  represents a service disruption time, and a vertical axis represents a CDF (Cumulative Distribution Function). A scenario  1  of  FIG. 10  represents an up message success and failure rate in case of using the maximum transmission power considering downlink according to the conventional art, and a scenario  2  represents an up message success and failure rate in case of using the maximum transmission power considering uplink according to the present invention. 
     Referring to  FIG. 9  and  FIG. 10 , it can be appreciated that, compared to the conventional art, a service disruption time is short in case of using the maximum transmission power considering uplink according to the present invention, an up message success rate is high, and a failure rate is low. 
     Table 1 below numerically expresses a service disruption time and an up message success and failure rate illustrated in  FIG. 9  and  FIG. 10 . 
     
       
         
               
               
               
             
               
               
               
               
             
           
               
                   
                 TABLE 1 
               
               
                   
                   
               
               
                   
                 Conventional art 
                 The invention 
               
               
                   
                   
               
             
             
               
                   
               
             
          
           
               
                   
                 0 message lost (%) 
                 63.46 
                 98.67 
               
               
                   
                 1 message lost (%) 
                 30.77 
                 1.33 
               
               
                   
                 2 message lost (%) 
                 5.77 
                 0.00 
               
               
                   
                 Average service 
                 0.0799 
                 0.0581 
               
               
                   
                 disruption time (sec) 
               
               
                   
                   
               
             
          
         
       
     
     Referring to Table 1 above, it can be appreciated that, in the present invention, the probability of up message reception success is high by 35.21%, the probability of once failure of up message transmitting is low by 29.44%, and there is no probability of twice failure, compared to the conventional art. Also, it can be appreciated that an average service disruption time is short by 0.0218 sec as well. 
     The present invention has an effect of being capable of increasing the probability that a target BS successfully receives and accordingly, being capable of decreasing a handover interruption time and improving a service quality, by determining the maximum transmission power of a handover message considering uplink of an MS and controlling a ranging code for ranging with a target BS and the transmission power of a ranging request message according to the determined maximum transmission power in a mobile communication system. Also, the present invention has an effect of being capable of decreasing unnecessary handover message exchange in wireless and efficiently making use of radio resources. 
     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.

Technology Category: h