TEPZZ _ 6594B_T EP B1 (19) (11) EP B1 (12) EUROPEAN PATENT SPECIFICATION

Transcription

1 (19) TEPZZ _ 694B_T (11) EP B1 (12) EUROPEAN PATENT SPECIFICATION (4) Date of publication and mention of the grant of the patent: Bulletin 13/47 (1) Int Cl.: H04W 2/ (09.01) H04W 36/ (09.01) H04W 2/14 (09.01) H04W 2/ (09.01) (21) Application number: (22) Date of filing: (4) Apparatus and method for handover in a wireless communication system Vorrichtung und Verfahren zur Übergabe in einem Funkkommunikationssystem Appareil et procédé de transfert dans un système de communication sans fil (84) Designated Contracting States: AT BE BG CH CY CZ DE DK EE ES FI FR GB GR HR HU IE IS IT LI LT LU LV MC MK MT NL NO PL PT RO SE SI SK TR () Priority: KR (43) Date of publication of application: Bulletin 09/2 (73) Proprietor: Samsung Electronics Co., Ltd. Suwon-si, Gyeonggi-do, (KR) (72) Inventors: Kim, Yu-Sin Gyeonggi-do (KR) Seo, Gwan-Gyu Gyeonggi-do (KR) (74) Representative: Gover, Richard Paul et al Harrison Goddard Foote LLP Saviour House 9 St Saviourgate York YO1 8NQ (GB) (6) References cited: EP-A WO-A1-00/7608 WO-A1-99/2226 US-A US-A EP B1 Note: Within nine months of the publication of the mention of the grant of the European patent in the European Patent Bulletin, any person may give notice to the European Patent Office of opposition to that patent, in accordance with the Implementing Regulations. Notice of opposition shall not be deemed to have been filed until the opposition fee has been paid. (Art. 99(1) European Patent Convention). Printed by Jouve, 7001 PARIS (FR)

2 Description 1. Field of the Invention: [0001] The present invention relates to an apparatus and method for handover of a Mobile Station (MS) in a wireless communication system. More particularly, the present invention relates to an apparatus and method for controlling the transmission power of an MS depending on a channel environment and improving a handover success rate Description of the Related Art: [0002] Generally, portable terminals supporting 2 nd Generation (2G) communication systems and 3 rd Generation (3G) communication systems perform handover within the same communication system or from one communication system to another. For example, portable terminals supporting Global System for Mobile communication (GSM) systems and Wideband Code Division Multiple Access (WCDMA) systems may perform handover between the GSM systems and may perform handover from a WCDMA system to a GSM system. [0003] FIG. 1 illustrates a signal flow during a handover from a GSM or WCDMA system to a GSM system according to the conventional art. [0004] Referring to FIG. 1, a Mobile Station (MS) 0 periodically reports information of a serving cell and an adjacent cell to a network 1 through step 121 during connection of a voice call. At this time, if a signal level of the serving cell is poor in a state where the MS 0 is accessing a GSM system, as in step 123, the MS 0 reports information in a format that is the same as in a legacy system to the network 1. If a signal level of the serving cell is poor in a state where the MS 0 is accessing a WCDMA system, as in step 12, the MS 0 reports signal information (i.e., an Event 3A) indicating that the serving cell has a value equal to or less than a threshold value, or signal information (i.e., an Event 3C) indicating that the adjacent cell has a value equal to or more than a threshold value, to the network 1. By doing so, in step 127, the MS 0 receives a handover command message from the network 1. [000] The MS 0 receiving the handover command message transmits a handover access message to the network 1 through steps 129 and 131. Then, the MS 0 starts a preset control timer (i.e., a T3124 timer) and, as in step 133, waits to receive a physical information message before the control timer expires. At this time, if the handover is an intra handover carried out between cells within a Base Station (BS), there is no need to perform a synchronization process. Therefore, the MS 0 directly proceeds to step 13 below without receiving the physical information message. [0006] In step 13, the MS 0 transmits a Set Asynchronous Balanced Mode (SABM) message attempting channel connection to the network 1 and then, waits to receive an Unnumbered Acknowledge (UA), which is a reply to the SABM, from the network 1 before a preset control timer (i.e., a T0 timer) expires. If the UA is not received, the MS 0 retransmits the SABM attempting channel connection through step 137. At this time, the MS 0 transmits the SABM a preset number of times until the UA is received. If, after transmitting the SABM the preset number of times, the UA is not received, the MS 0 returns to a previous serving cell. [0007] If receiving a UA that is a reply message from the network 1 through step 139, the MS 0 transmits a handover complete message to the network 1 and completes a handover procedure through step 141. [0008] As described above, handover is performed if a signal level received by an MS from a serving cell is worse than that of an adjacent cell, and fails if a reply to a handover message transmitted by the MS is not received by the MS within a threshold time period. Also, the MS performs the handover using a predefined output power, i.e., the transmission power corresponding to a power control level received through a Slow Associated Control Channel (SACCH) from a network. [0009] In the case of using a technique for performing handover depending on a Receive Signal Strength Indicator (RSSI) of the MS and reception or non-reception of a reply message as above, there is a problem in that, even if the RSSI of the MS is high, the handover may fail because of the transmission signal quality of the MS. For example, if the transmission signal quality of the MS is poor, handover may fail because the MS fails to transmit the handover access messages of steps 129 and 131 or the SABMs of steps 13 and 137, and thus fails to receive any replies. [00] US-06/ A1 discloses a method and system for mobile communications. The method and includes a method for determining a radio zone and an uplink transmission power in which bases stations transmit broadcast information, a mobile station receives the broadcast information, detects the reception levels, calculates respective path losses and selects a radio zone in which the necessary uplink transmission power level is minimal. SUMMARY OF THE INVENTION [0011] An aim of embodiments of the present invention is to address at least the above-mentioned problems and/or disadvantages and to provide at least the advantages described below. Accordingly, an aim of embodiments of the present invention is to provide an apparatus and method for handover of a Mobile Station (MS) in a wireless communication 2

3 1 2 system. [0012] Another aim of embodiments of the present invention is to provide an apparatus and method for controlling the transmission power of an MS and for improving a handover success rate in a wireless communication system. [0013] A further aim of embodiments of the present invention is to provide an apparatus and method for, upon handover, controlling transmission power of an MS depending on channel circumstances in a wireless communication system. [0014] Yet another aim of embodiments of the present invention is to provide an apparatus and method for, upon handover, controlling the transmission power of an MS depending on reception or non-reception of a handover reply message in a wireless communication system. [001] The above aspects are achieved by providing an apparatus and method for handover in a wireless communication system. [0016] In accordance with a first aspect of the present invention, a method for performing handover by a Mobile Station MS in a wireless communication system is provided. The method includes: upon receiving a handover command message, estimating a channel by measuring a Bit Error Rate BER for the channel; controlling a transmission power of the MS depending on the channel estimation result; transmitting a handover access message using the controlled transmission power; determining if a physical information message is received within a time period; and when the physical information message is not received, terminating handover, moving to a previously accessed cell, and increasing the transmission power. [0017] In accordance with a second aspect of the present invention, an apparatus for performing handover in a wireless communication system is provided. The apparatus includes: a controller for, upon receiving a handover command message, estimating a channel by measuring a Bit Error Rate BER for the channel and controlling a transmission power of a Mobile Station depending on the channel estimation result; and a transmitter/receiver for transmitting a handover access message using the controlled transmission power depending on the control of the controller, wherein the controller controls the transmitter/receiver and transmits the handover access message using the controlled transmission power and, when a physical information message is not received within a time period, terminates handover, moves to a previously accessed cell, and increases a transmit power. [0018] 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 3 [0019] The above and other aspects, features and advantages of certain exemplary embodiments of the present invention will be more apparent from the following description taken in conjunction with the accompanying drawings, in which: FIG. 1 is a ladder diagram illustrating a signal flow for handover from a Global System for Mobile communication (GSM) or Wideband Code Division Multiple Access (WCDMA) system to a GSM system according to the conventional art; FIG. 2 is a block diagram illustrating a construction of a Mobile Station (MS) in a wireless communication system according to an exemplary embodiment of the present invention; and FIG. 3 is a flow diagram illustrating a procedure for handover of an MS in a wireless communication system according to an exemplary embodiment of the present invention. 4 [00] Throughout the drawings, it should be noted that like reference numbers are used to depict the same or similar elements, features and structures. DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS 0 [0021] 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 of the invention. Also, descriptions of well-known functions and constructions are omitted for clarity and conciseness. [0022] 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 3

4 1 2 3 appended claims and their equivalents. [0023] 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. [0024] A technology for controlling transmission power of a Mobile Station (MS) considering a channel environment in a wireless communication system according to an exemplary embodiment of the present invention is described below. An exemplary embodiment of the present invention is applicable to handover between 2 nd Generation (2G) communication systems and handover between a 3 rd Generation (3G) communication system and a 2G communication system. In the following description, handover between Global System for Mobile communication (GSM) systems is described, for example. [002] FIG. 2 is a block diagram illustrating a construction of an MS in a wireless communication system according to an exemplary embodiment of the present invention. [0026] Referring to FIG. 2, the MS includes a controller (i.e., a MicroProcessor Unit (MPU)) 0, a transmitter/receiver 6, a storage unit 8, a first timer 2, and a second timer 212. The controller 0 includes a handover power controller 2 and a message processor 4. [0027] The controller 0 performs a general operation of the MS, e.g., a process and control for voice telephony, data communication, and handover. Particularly, according to an exemplary embodiment of the present invention, the controller 0 includes the handover power controller 2 and the message processor 4. Thus, upon handover execution, the controller 0 executes a process of controlling transmission power of the MS depending on a channel environment. That is, the controller 0 increases or maintains the transmission power of the MS through the handover power controller 2, and generates and analyzes a message for handover through the message processor 4. Also, the controller 0 determines the need for retransmission of a message and a handover failure or success using the first and second timers 2 and 212 and processes and controls an operation depending on the results. [0028] When a handover command message is received, the handover power controller 2 increases or maintains the transmission power of the MS. In an exemplary implementation, the handover power controller 2 determines the transmission power by measuring Bit Error Rates (BERs) for a continuous number of channels, determining an average BER based on the measured BERs, comparing the average BER with a threshold value, and setting a power control level based on the comparison. Also, if physical information is not received before the expiration of the first timer 2 and if an Unnumbered Acknowledge (UA) message is not received before the expiration of the second timer 212 so that a return to a previous cell is determined, the handover power controller 2 increases the transmission power by increasing the power control level. At this time, an increase width of the power control level may be set and changed by a user or a service provider. For example, the power control level may increase by only one level or may increase by three levels at one time. [0029] The handover power controller 2 manages initialization and change setting of variables for increasing or maintaining a power control level for determining a transmission power of the MS. For example, the handover power controller 2 manages variables for a power control level increase as in Table 1 below. 4 Table 1 Variable Value Description Power_Level_Controller 00 No power control level change 01 Power control level increase Power control level decrease Bad_BER_Ind 00 Average BER Threshold value 01 Average BER < Threshold value 0 4

5 (continued) Variable Value Description SABM_Retrans_Failure_Counter 000 No failure st failure 0 2 nd failure rd failure 0 4 th failure 1 th failure 1 6 th failure th failure [00] Here, the Power_Level_Controller denotes a variable used for determining a current power control level. If the Power_Level_Controller value is equal to 00, the current power control level is maintained. If it is equal to 01, the current power control level is increased and if it is equal to, the current power control level is decreased. A GSM system is described as an example. If a power control level is initially set to 3 and the transmission power is equal to 37 dbm, when the Power_Level_Controller value is set to 01, the power control level increases by one level and becomes 4, so the transmission power changes from the 37 dbm to 3 dbm. Here, the handover power controller 2 sets the Power_Level_Controller value to 01 or, increases or decreases the transmission power, and initializes the Power_Level_Controller value by 00. [0031] The Bad_BER_Ind denotes a variable used for determining a current Radio Frequency (RF) interference environment for a transmit Dedicated Control Channel (DCCH) or Slow Associated Control Channel (SACCH) of a serving cell. The Bad_BER_Ind is set to 00 or 01 depending on an average BER value, thus having influence on an increase of a power control level. That is, if the Bad_BER_Ind is set to 01, the handover power controller 2 sets the Power_Level_Controller value to 01, increasing the power control level by one level. [0032] The SABM_Retrans_Failure_Counter, which is a counter representing a transmission failure of SABM, increases whenever a reply to Set Asynchronous Balanced Mode (SABM) transmission is not received before the expiration of the second timer 212 and, if a handover process is terminated, is initialized to 0. [0033] The message processor 4 generates a message necessary for handover (e.g., a measurement report message, a handover access message, a Set Asynchronous Balanced Mode (SABM) message, and a handover complete message), provides the generated message to the transmitter/receiver 6, receives a handover message (e.g., a handover command message, a physical information message, and a UA message) from the transmitter/receiver 6, and analyzes the handover message. [0034] The transmitter/receiver 6 performs a role of transmitting/receiving a message with a network depending on the control of the controller 0. Particularly, the transmitter/receiver 6 transmits handover messages to the network using a transmission power controlled by the handover power controller 2. [003] The storage unit 8 stores a program necessary for a general operation of the MS and a variety of kinds of information, stores a table representing the transmission power depending on the power control level according to an exemplary embodiment of the present invention, and stores a threshold value for comparison with the BER and threshold number of times for limiting the number of SABM transmissions. [0036] The first timer 2 and second timer 212 measure time depending on the control of the controller 0. [0037] FIG. 3 is a flow diagram illustrating a procedure for handover of an MS in a wireless communication system according to an exemplary embodiment of the present invention. [0038] Referring to FIG. 3, in a state where a voice call is in progress in step 1, if it is determined that a handover command message is received from a network, the MS proceeds to step 3 and determines a BER for a continuous number of channels. At this time, the MS may use a transmit DCCH (i.e., SACCH) or Traffic Channel (TCH) of a serving cell for the BER measurement. Also, whether to use any channel or use any number of transmission frames may be arbitrarily changed and set by a user. For example, in a GSM system, the MS may measure a BER for n number of SACCH frames repeated every 13th frame among 26 frames or may measure the BER for a continuous k number of TCH frames among the 26 frames. Similarly, in a WCDMA system, the MS may measure a BER for a continuous n number of TCH frames. That is, the MS may measure a BER for a number of frames repeated at a period of n among a continuous k number of frames. [0039] In step, the MS determines if an average of the measured BER is greater than or equal to a threshold value. If the average of the BER is greater than or equal to the threshold value, in step 7, the MS increases a power

6 1 2 3 control level, increases transmission power and, in step 9, transmits a handover access (Handover_Access) message to a network using the increased transmission power and operates a first timer 2. On the other hand, if the average of the BER is determined to be less than the threshold value in step, the MS proceeds to step 9 without increasing the transmission power, thus transmitting a handover access message using the maintained transmission power and operating the first timer 2. Here, the MS increases the transmission power or maintains as it is as above, by setting a variable (Bad_BER_Ind) representing an RF interference environment to 00 or 01 depending on the average BER and increasing or maintaining a power control level. [00] In step 311, the MS determines if a physical information message is received before the expiration of the first timer 2. Here, if the handover is an intra handover, which is a handover carried out between cells within a BS, there is no need to perform a synchronization process and thus the MS omits step 311 and proceeds to subsequent step 313. [0041] If a physical information message is not received before the expiration of the first timer 2, in step 323, the MS terminates a handover procedure, returns to a previous cell, increases the power control level, increases a current transmission power, and terminates the process according to an exemplary embodiment of the present invention. Here, the MS may increase the transmission power, by setting a variable (i.e., a Power_Level_Controller) determining a current power control level to 01 and increasing a current power level. [0042] If a physical information message is received before the expiration of the first timer 2, in step 313, the MS transmits an SABM message attempting channel connection and operates a second timer 212. The MS proceeds to step 31 and determines if a UA message, which is a reply message to the SABM, is received before the expiration of the second timer 212. If the UA message is received, the MS proceeds to step 32, thus transmitting a handover complete message and terminating the process according to an exemplary embodiment of the present invention. As above, if a physical information message is received or a UA message is received, the MS sets a variable (i.e., a Power_Level_ Controller) determining a current power control level to 00 and maintains the transmission power without changing a current power level. [0043] If the UA message is not received until the second timer 212 expires, the MS proceeds to step 317 and determines if the number of times the MS has transmitted an SABM is less than a threshold number of times. If the number of times of transmitting the SABM is less than the threshold number of times, the MS proceeds to step 319, increases a counter (i.e., an SABM_Retrans_Failure_Counter) representing a failure of the SABM transmission, increases a power control level, and increases the transmission power. In step 321, the MS retransmits the SABM message using the increased transmission power, initializes and again operates the second timer 212, returns to step 31, and again performs the subsequent steps. Here, the MS may increase the transmission power by setting a variable (i.e., a Power_Level_Controller) determining a current power control level to 01 and increasing a current power level. [0044] If the number of times of transmitting the SABM is greater than or is equal to the threshold number of times in step 317, that is, if the SABM is transmitted the threshold number of times, the MS proceeds to step 323, terminates the handover procedure, returns to a previous cell, increases the power control level, increases the current transmission power, and terminates the process according to an exemplary embodiment of the present invention. [004] An exemplary embodiment of the present invention has an effect of, upon handover, controlling the transmission power of an MS considering a channel environment and reception or non-reception of a handover reply message, thereby being capable of improving a handover success rate in a wireless communication system. [0046] While the invention has been shown and described with reference to certain exemplary embodiments thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the scope of the invention as defined by the appended claims and their equivalents. 4 Claims 1. A method for performing handover by a Mobile Station MS 0 in a wireless communication system, the method comprising: 0 upon receiving (1) a handover command message, estimating a channel by measuring (3) a Bit Error Rate BER for the channel ; controlling (,7) a transmission power of the MS depending on the channel estimation result; transmitting (9) a handover access message using the controlled transmission power; determining (311) if a physical information message is received within a time period; and when the physical information message is not received, terminating handover, moving (323) to a previously accessed cell, and increasing the transmission power. 2. The method of claim 1, wherein the estimating the channel comprises measuring (3) a Bit Error Rate BER for a number of frames repeated every constant period among a continuous number of frames for a corresponding channel. 6

7 3. The method of claim 2, wherein the controlling (,7) the transmission power of the MS comprises: comparing () an average of the measured BER with a threshold value; and determining to either, increase (7) or maintain the transmission power for a next transmit frame depending on the comparison result. 4. The method of claim 1, further comprising: 1 transmitting (313) a Set Asynchronous Balanced Mode SABM message using the controlled transmission power; when an Unnumbered Acknowledge UA message is not received within a time period, comparing (317) the number of times of transmitting the SABM message with a threshold; and when the number of times of SABM transmission is less than the threshold, increasing (319) the transmission power for a next transmission frame, and retransmitting (321) the SABM message using the increased transmission power.. The method of claim 4, further comprising: when the number of times of SABM transmission is greater than or equal to the threshold, moving (323) to a previously accessed cell and increasing a transmission power. 6. The method of claim 1 wherein the controlling (, 7) the transmission power of the MS comprises at least one of increasing (7) and decreasing a power control power of the MS comprises at least one of increasing (7) and decreasing a power control level by a preset level The method of claim 1, wherein the handover comprises at least one of a handover between 2 nd Generation 2G systems and handover between a 3 rd Generation 3G system and a 2G system. 8. An apparatus for performing handover in a wireless communication system, the apparatus comprising: 3 a controller (0) for, upon receiving a handover command message, estimating a channel by measuring (3) a Bit Error Rate BER for the channel and controlling (,7) a transmission power of a Mobile Station depending on the channel estimation result; and a transmitter/receiver (6) for transmitting (9) a handover access message using the controlled transmission power depending on the control of the controller (0), wherein the controller (0) controls the transmitter/receiver (6) and transmits the handover access message using the controlled transmission power and, when a physical information message is not received within a time period, terminates handover, moves (323) to a previously accessed cell, and increases a transmit power. 9. The apparatus of claim 8, wherein the controller (0) measures (3) a Bit Error Rate BER for a number of frames repeated every constant period among a continuous number of frames for a corresponding channel, compares an average of the measured BER with a threshold value, and determines () to either increase (7) or maintain the transmission power for a next transmit frame. 4. The apparatus of claim 8, wherein the controller (0) controls the transmitter/receiver (6) and transmits (313) a Set Asynchronous Balanced Mode SABM message using the controlled transmit power and, when an Unnumbered Acknowledge UA message is not received within a time period, compares (317) the number of times of transmitting the SABM message with a threshold number of times and, when the number of times of SABM transmission is less than the threshold number of times, increases (319) the controlled transmit power and retransmits (321) the SABM message The apparatus of claim, wherein, when the number of times of SABM transmission is equal to the threshold number of times, the controller (0) moves to a previously accessed cell and increases the controlled transmission power. 12. The apparatus of claim 8, wherein the controller (0) either increases or decreases a power control level by a preset level and controls the transmission power of the MS (0). 13. The apparatus of claim 8, wherein the handover comprises one of handover between 2 nd Generation 2G systems and handover between a 3 rd Generation 3G system and a 2G system. 7

8 Patentansprüche 1. Verfahren zum Durchführen einer Übergabe durch eine Mobilstation MS 0 in einem Drahtloskommunikationssystem, wobei das Verfahren Folgendes umfasst: nach dem Empfangen (1) einer Übergabebefehlnachricht Schätzen eines Kanals durch Messen (3) einer Bitfehlerrate (Bit Error Rate - BER) für den Kanal, Regeln (, 7) einer Übertragungsleistung der MS in Abhängigkeit von dem Kanalschätzergebnis, Übertragen (9) einer Übergabezugangsnachricht unter Verwendung der geregelten Übertragungsleistung, Bestimmen (311), ob innerhalb eines Zeitraums eine physische Informationsnachricht empfangen wird, und wenn die physische Informationsnachricht nicht empfangen wurde, Abbrechen der Übergabe, Übergehen (323) zu einer zuvor aufgerufenen Zelle und Erhöhen der Übertragungsleistung Verfahren nach Anspruch 1, bei dem das Schätzen des Kanals das Messen (3) einer Bitfehlerrate BER für eine Anzahl in jedem konstanten Intervall wiederholter Rahmen unter einer kontinuierlichen Anzahl Rahmen für einen entsprechenden Kanal umfasst. 3. Verfahren nach Anspruch 2, bei dem das Regeln (, 7) der Übertragungsleistung der MS Folgendes umfasst: Vergleichen () eines Mittelwertes der gemessenen BER mit einem Schwellwert und Bestimmen in Abhängigkeit von dem Ergebnis des Vergleichs, dass die Übertragungsleistung für einen nächsten Übertragungsrahmen entweder erhöht (7) oder beibehalten wird Verfahren nach Anspruch 1, das ferner Folgendes umfasst: Übertragen (313) einer SABM-Nachricht (Set Asynchronous Balanced Mode) unter Verwendung der geregelten Übertragungsleistung, wenn nicht innerhalb eines Zeitraums eine UA-Nachricht (Unnumbered Acknowledge) empfangen wird, Vergleichen (317) der Anzahl der Übertragungen der SABM-Nachricht mit einem Schwellwert, und wenn die Anzahl der SABM-Übertragungen unter dem Schwellwert liegt, Erhöhen (319) der Übertragungsleistung für einen nächsten Übertragungsrahmen und erneutes Übertragen (321) der SABM-Nachricht unter Verwendung der erhöhten Übertragungsleistung. 3. Verfahren nach Anspruch 4, das ferner Folgendes umfasst: wenn die Anzahl SABM-Übertragungen größer als der oder gleich dem Schwellwert ist, Übergehen (323) zu einer zuvor aufgerufenen Zelle und Erhöhen der Übertragungsleistung. 6. Verfahren nach Anspruch 1, bei dem das Regeln (, 7) der Übertragungsleistung der MS das Erhöhen (7) und/oder Verringern einer Leistungsregelstufe um eine vorgegebene Stufe umfasst. 7. Verfahren nach Anspruch 1, bei dem die Übergabe eine Übergabe zwischen 2G-Systemen der 2. Generation und/ oder eine Übergabe zwischen einem 3G-System der 3. Generation und einem 2G-System umfasst Vorrichtung zum Durchführen einer Übergabe in einem Drahtloskommunikationssystem, die Folgendes umfasst: eine Steuereinheit (0) zum Schätzen eines Kanals durch Messen (3) einer Bitfehlerrate BER für den Kanal nach dem Empfangen einer Übergabebefehlsnachricht und zum Regeln (, 7) einer Übertragungsleistung einer Mobilstation in Abhängigkeit von dem Ergebnis der Kanalschätzung und einen Sender/Empfänger (6) zum Übertragen (9) einer Übergabezugangsnachricht unter Verwendung der geregelten Übertragungsleistung in Abhängigkeit von der Regelung durch die Steuereinheit (0), wobei die Steuereinheit (0) den Sender/Empfänger (6) steuert und die Übergabezugangsnachricht unter Verwendung der geregelten Übertragungsleistung überträgt und, wenn nicht innerhalb eines Zeitraums eine physische Informationsnachricht empfangen wird, die Übergabe abbricht, zu einer zuvor aufgerufenen Zelle übergeht (323) und eine Übertragungsleistung erhöht. 9. Vorrichtung nach Anspruch 8, bei der die Steuereinheit (0) eine Bitfehlerrate BER für eine Anzahl in jedem konstanten Intervall wiederholter Rahmen unter einer kontinuierlichen Anzahl Rahmen für einen entsprechenden Kanal misst (3), einen Mittelwert für die gemessene BER mit einem Schwellwert vergleicht und bestimmt (), 8

9 dass die Übertragungsleistung für einen nächsten Übertragungsrahmen entweder erhöht (7) oder beibehalten wird. 1. Vorrichtung nach Anspruch 8, bei der die Steuereinheit (0) den Sender/Empfänger (6) steuert und unter Verwendung der geregelten Übertragungsleistung eine SABM-Nachricht (Set Asynchronous Balanced Mode) überträgt (313) und, wenn nicht innerhalb eines Zeitraums eine UA-Nachricht (Unnumbered Acknowledge) empfangen wird, die Anzahl der Übertragungen der SABM-Nachricht mit einem Schwellwert dafür vergleicht (317) und, wenn die Anzahl der SABM-Übertragungen unter dem Schwellwert dafür liegt, die geregelte Übertragungsleistung erhöht (319) und die SABM-Nachricht erneut überträgt (321). 11. Vorrichtung nach Anspruch, bei der die Steuereinheit (0), wenn die Anzahl der SABM-Übertragungen dem Schwellwert dafür entspricht, zu einer zuvor aufgerufenen Zelle übergeht und die geregelte Übertragungsleistung erhöht. 12. Vorrichtung nach Anspruch 8, bei der die Steuereinheit (0) eine Leistungsregelstufe um eine vorgegebene Stufe entweder erhöht oder verringert und die Übertragungsleistung der MS (0) regelt. 13. Vorrichtung nach Anspruch 8, bei der die Übergabe eine Übergabe zwischen 2G-Systemen der 2. Generation oder eine Übergabe zwischen einem 3G-System der 3. Generation und einem 2G-System umfasst. Revendications 2 1. Procédé de réalisation d un transfert par un poste mobile, MS, 0 dans un système de communications sans fil, le procédé comprenant les opérations consistant à : 3 lors de la réception (1) d un message d instruction de transfert, effectuer l estimation d un canal en mesurant (3) un taux d erreurs sur les bits, BER, pour le canal ; contrôler (, 7) une puissance de transmission pour le MS en fonction du résultat de l estimation faite sur le canal ; émettre (9) un message d accès de transfert grâce à l utilisation de la puissance de transmission contrôlée ; déterminer (311) si un message d information physique est reçu dans les limites d un intervalle de temps ; et lorsque le message d information physique n est pas reçu, mettre fin au transfert, passer (323) à une cellule à laquelle on a précédemment eu accès, et augmenter la puissance de transmission. 2. Procédé selon la revendication 1, l estimation du canal comprenant l opération consistant à mesurer (3) un taux d erreurs sur les bits, BER, pour un certain nombre de trames répétées chaque période constante parmi un nombre continu de trames pour un canal correspondant. 3. Procédé selon la revendication 2, le contrôle (, 7) de la puissance de transmission du MS comprenant les opérations consistant à : 4 comparer () une moyenne du BER mesuré à une valeur-seuil ; et déterminer soit d augmenter (7), soit de maintenir, la puissance de transmission pour une prochaine trame de transmission en fonction du résultat de la comparaison. 4. Procédé selon la revendication 1, comprenant en outre les opérations consistant à : 0 émettre (313) un message d établissement de mode asynchrone symétrique, SABM, grâce à l utilisation de la puissance de transmission contrôlée ; lorsqu un message d accusé de réception non numéroté, UA, n est pas reçu dans les limites d un intervalle de temps, comparer (317) le nombre de reprises de transmission du message SABM à un seuil ; et lorsque le nombre de reprises de transmission SABM est inférieur au seuil, augmenter (319) la puissance de transmission pour une prochaine trame de transmission, et ré-émettre (321) le message SABM grâce à l utilisation de la puissance de transmission augmentée.. Procédé selon la revendication 4, comprenant en outre les opérations consistant à : lorsque le nombre de reprises de transmission SABM est supérieur ou égal au seuil, passer (323) à une cellule à laquelle on a précédemment eu 9

10 accès, et augmenter une puissance de transmission. EP B1 6. Procédé selon la revendication 1, le contrôle (, 7) de la puissance de transmission du MS comprenant au moins l une des opérations suivantes, à savoir une augmentation (7) et une diminution d un niveau de contrôle de puissance suivant un niveau prédéfini. 7. Procédé selon la revendication 1, le transfert comprenant au moins l une des opérations suivantes, à savoir un transfert entre des systèmes de 2e génération, 2G, et un transfert entre un système de 3e génération, 3G, et un système 2G. 8. Appareil de réalisation d un transfert dans un système de communications sans fil, l appareil comprenant : 1 un contrôleur (0) qui, lors de la réception d un message d instruction de transfert, effectue l estimation d un canal en mesurant (3) un taux d erreurs sur les bits, BER, pour le canal, et contrôle (, 7) une puissance de transmission pour un poste mobile en fonction du résultat de l estimation faite sur le canal ; et un émetteur/récepteur (6) pour émettre (9) un message d accès de transfert grâce à l utilisation de la puissance de transmission contrôlée en fonction du contrôle effectué par le contrôleur (0), cas dans lequel le contrôleur (0) assure le pilotage de l émetteur/récepteur (6) et émet le message d accès de transfert grâce à l utilisation de la puissance de transmission contrôlée et, lorsqu un message d information physique n est pas reçu dans les limites d un intervalle de temps, met fin au transfert, passe (323) à une cellule à laquelle on a précédemment eu accès, et augmente une puissance de transmission Appareil selon la revendication 8, le contrôleur (0) mesurant (3) un taux d erreurs sur les bits, BER, pour un certain nombre de trames répétées chaque période constante parmi un nombre continu de trames pour un canal correspondant, comparant une moyenne du BER mesuré à une valeur-seuil, et déterminant () soit d augmenter (7), soit de maintenir, la puissance de transmission pour une prochaine trame de transmission. 3. Appareil selon la revendication 8, le contrôleur (0) assurant le pilotage de l émetteur/récepteur (6) et émettant (313) un message d établissement de mode asynchrone symétrique, SABM, grâce à l utilisation de la puissance de transmission contrôlée et, lorsqu un message d accusé de réception non numéroté, UA, n est pas reçu dans les limites d un intervalle de temps, comparant (317) le nombre de reprises de transmission du message SABM à un nombre de reprises de seuillage, et, lorsque le nombre de reprises de transmission SABM est inférieur au nombre de reprises de seuillage, augmentant (319) la puissance de transmission contrôlée et ré-émettant (321) le message SABM. 11. Appareil selon la revendication, lorsque le nombre de reprises de transmission SABM est égal au nombre de reprises de seuillage, le contrôleur (0) passant à une cellule à laquelle on a précédemment eu accès et augmentant la puissance de transmission contrôlée. 12. Appareil selon la revendication 8, le contrôleur (0) effectuant soit une augmentation, soit une diminution, d un niveau de contrôle de puissance suivant un niveau prédéfini, et pilotant la puissance de transmission du MS (0) Appareil selon la revendication 8, le transfert comprenant l une des opérations suivantes, à savoir un transfert entre des systèmes de 2e génération, 2G, et un transfert entre un système de 3e génération, 3G, et un système 2G. 0

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14 REFERENCES CITED IN THE DESCRIPTION This list of references cited by the applicant is for the reader s convenience only. It does not form part of the European patent document. Even though great care has been taken in compiling the references, errors or omissions cannot be excluded and the EPO disclaims all liability in this regard. Patent documents cited in the description US A1 [00] 14