Patent Publication Number: US-7899482-B2

Title: Transmission power target value variable control apparatus and method and mobile communication terminal

Description:
TECHNICAL FIELD 
     The present invention relates to a transmission power target value variable control apparatus and a method thereof and, more particularly, to a target value variable control scheme of variably controlling a target value for transmission power control in a radio channel between a mobile communication terminal and a base station in accordance with an actual reception quality. 
     BACKGROUND ART 
     A W-CDMA (Wideband-Code Division Multiple Access) communication scheme has already been developed and come into service as a mobile communication means of third generation. The transmission power control scheme of the W-CDMA communication system includes inner loop control and outer loop control. 
     In inner loop control, an increase/decrease of the power of a base station from which a portable terminal directly receives a radio wave is controlled in a short period. More specifically, a T-SIR (Target SIR (Signal to Interference Ratio)) is used as a control target value. The T-SIR is compared with a reception SIR measured from a reception signal in the portable terminal. If the reception SIR is lower than the T-SIR, a request to raise the transmission power is issued to the base station. If the reception SIR is higher than the T-SIR, a request to reduce the transmission power is issued to the base station. 
     In outer loop control, an appropriate T-SIR to be used as a target value of inner loop control is determined on the basis of the long-term average of BLERs (BLock Error Rates). More specifically, a required reception quality (Target BLER (T-BLER)) is obtained from a base station. If a BLER measured in a portable terminal is higher than the T-BLER, the T-SIR is raised. If the measured BLER is lower than the T-BLER, the T-SIR is reduced. 
     Conventional outer loop control will be described in more detail with reference to  FIG. 8 . A despreading unit  1101  despreads a reception signal and sends the generated signal to a Rake reception unit  1102 . The Rake reception unit  1102  Rake-receives and demodulates the signal and sends it to a long section quality measuring unit  1103 . The long section quality measuring unit  1103  calculates the BLER of the demodulated signal for a predetermined period and sends the calculation result, i.e., a measured BLER  1203  to a comparison determination unit  1105 . 
     A T-BLER  1104  holds a T-BLER that is a required reception quality obtained from a signal from the base station. The T-BLER  1104  sends a T-BLER  1204  as a required reception quality to the comparison determination unit  1105 . The comparison determination unit  1105  compares the measured BLER  1203  calculated by the long section quality measuring unit  1103  with the T-BLER  1204  and sends a comparison result  1205  to a T-SIR generation unit  1106 . The T-SIR generation unit  1106  calculates a T-SIR  1206  from the comparison result  1205  and sends it to the inner loop control side (not shown). 
     In this example, the long-term average of BLERs is used as a reception quality in outer loop control. Reference 1 (Japanese Patent Laid-Open No. 2003-32184) proposes a technique using a BER (Bit Error Rate) as a reception quality. 
     DISCLOSURE OF INVENTION 
     Problems to be Solved by the Invention 
     Problems of the conventional outer loop control described with reference to  FIG. 8  will be explained. If the reception field from a base station is strong, and the BLER is low because of the channel design of a communication carrier (telecommunications carrier), the following problems arise. In outer loop control, when the reception field is strong, and the BLER is low, the T-SIR is continuously reduced to the lower limit value. Assume that the reception SIR abruptly deteriorates due to interference from another base station or terminal. The outer loop control is going to raise the T-SIR but cannot follow the abrupt degradation of the reception SIR because the control uses the long-term average of BLERs. The reception SIR drops below the limit value of the portable terminal before the T-SIR rises. Consequently, the portable terminal cannot receive the signal from the base station. If the user is using the portable terminal for, e.g., a call, the service is interrupted. 
       FIG. 9  shows this state.  FIG. 9  shows a change in reception SIR with respect to time (t). “T” indicates the above-described lower limit value of T-SIR, and “G” indicates the SIR limit value of the portable terminal. When the T-SIR has the lower limit value T, the BLER abruptly deteriorates at time t 1  due to interference from another base station or terminal. From then on, the outer loop cannot follow with the T-SIR control period. From time t 2  when the T-SIR drops below the portable terminal limit value G, the portable terminal cannot receive the signal from the base station, and the service is interrupted. 
     The technique described in reference 1 uses, as a reception quality, a BER in place of the long-term average of BLERs and therefore ensures rapid follow-up. However, if a BER is used in a normal state, the T-SIR exhibits a very vigorous time-rate change. Power control in inner loop control frequently varies, resulting in instability. Additionally, power consumption for transmission power control in the base station or portable terminal enormously increases. 
     The present invention has been made to solve these problems, and has as its object to prevent service interruption even when a reception SIR abruptly deteriorates in a place where the reception field from a base station is strong, and the reception quality is high. 
     It is another object of the present invention to execute stable transmission power control normally. 
     Means of Solution to the Problems 
     In order to achieve the above objects, according to the present invention, there is provided a transmission power target value variable control apparatus characterized by comprising target value generation means for generating, on the basis of an actual reception quality in a mobile communication terminal, a target value to be used to control transmission power of a base station from the mobile communication terminal, and target value correction means for adding a correction value to the target value generated by the target value generation means in a predetermined case. 
     According to the present invention, there is also provided a mobile communication terminal characterized by comprising target value generation means for generating, on the basis of an actual reception quality, a target value to be used to control transmission power of a base station, and target value correction means for adding a correction value to the target value generated by the target value generation means in a predetermined case. 
     According to the present invention, there is also provided a transmission power target value variable control method characterized by comprising the steps of generating, on the basis of an actual reception quality in a mobile communication terminal, a target value to be used to control transmission power of a base station from the mobile communication terminal, and adding a correction value to the generated target value in a predetermined case. 
     EFFECT OF THE INVENTION 
     In the present invention, a target value is corrected by adding a correction value to it. Even when a reception SIR abruptly deteriorates in a communication carrier with a strong reception field and a low BLER, it does not drop below the SIR limit value of the mobile communication terminal. Hence, the terminal can receive the signal from the base station and continue a service such as speech communication. 
     In the present invention, the actual reception quality is measured on the basis of the number of errors that have occurred in a reception signal in every predetermined time and used for target value generation. Hence, stable transmission power control can be done normally. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a block diagram showing the arrangement of the main part of a portable terminal according to an embodiment of the present invention; 
         FIG. 2  is a block diagram showing an arrangement of an outer loop control unit in  FIG. 1 ; 
         FIG. 3  is a block diagram showing an arrangement of a T-SIR output unit in  FIG. 2 ; 
         FIG. 4  is a graph for explaining the operation of the outer loop control unit in  FIG. 2 ; 
         FIG. 5  is a block diagram showing an arrangement of the outer loop control unit of a portable terminal according to another embodiment of the present invention; 
         FIG. 6  is a block diagram showing an arrangement of a detection unit in  FIG. 5 ; 
         FIG. 7  is a block diagram showing an arrangement of a control unit in  FIG. 5 ; 
         FIG. 8  is a block diagram of a prior art; and 
         FIG. 9  is a graph for explaining the problems of the prior art shown in  FIG. 8 . 
     
    
    
     BEST MODE FOR CARRYING OUT THE INVENTION 
     The embodiments of the present invention will be described below with reference to the accompanying drawings. 
     A portable terminal (mobile communication terminal)  1  according to an embodiment of the present invention employs a W-CDMA communication scheme and includes a transmission power control unit  10  and an antenna  20  connected to the transmission power control unit  10 , as shown in  FIG. 1 . The transmission power control unit  10  includes an inner loop control unit  11  and an outer loop control unit (transmission power target value variable control apparatus)  12 . 
     The inner loop control unit  11  controls, in a short period, an increase/decrease of the power of a base station from which the portable terminal  1  directly receives a radio wave. More specifically, a T-SIR is used as a control target value. The T-SIR is compared with a reception SIR measured from a reception signal in the portable terminal  1 . If the reception SIR is lower than the T-SIR, a request to raise the transmission power is issued to the base station. If the reception SIR is higher than the T-SIR, a request to reduce the transmission power is issued to the base station. 
     The outer loop control unit  12  determines, on the basis of the long-term average of BLERs, an appropriate T-SIR to be used as a target value in the inner loop control unit  11 . More specifically, a required reception quality T-BLER is obtained from the base station. If a BLER measured in the portable terminal  1  is higher than the T-BLER, the T-SIR is raised. If the measured BLER is lower than the T-BLER, the T-SIR is reduced. Additionally, a correction value is added to the T-SIR in a predetermined case. 
     As shown in  FIG. 2 , the outer loop control unit  12  includes a despreading unit  101 , Rake reception unit  102 , long section quality measuring unit  103 , T-BLER holding unit  104 , comparison determination unit  105 , T-SIR output unit  106 , USIM (Universal Subscriber Identify Module)  107 , control unit  108 , and detection unit  109 . 
     The despreading unit  101  despreads a reception signal and sends the generated signal to the Rake reception unit  102 . The Rake reception unit  102  Rake-receives and demodulates the signal and sends it to the long section quality measuring unit  103 . The long section quality measuring unit  103  measures the actual reception quality on the basis of the number of errors that have occurred in the demodulated signal in every predetermined time and sends the reception quality to the comparison determination unit  105 . More specifically, the long section quality measuring unit  103  calculates the BLER of the demodulated signal for a predetermined time and sends the calculation result, i.e., a measured BLER  203  to the comparison determination unit  105 . 
     The T-BLER holding unit  104  holds a T-BLER that is a required reception quality obtained from a signal from the base station. The T-BLER holding unit  104  sends a T-BLER  204  as a required reception quality to the comparison determination unit  105 . The comparison determination unit  105  compares the measured BLER  203  calculated by the long section quality measuring unit  103  with the T-BLER  204  and sends a comparison result  205  to the T-SIR output unit  106 . 
     The USIM  107  is an extended SIM (Subscriber Identify Module) card oriented to third-generation mobile communications. The USIM  107  stores information about a communication carrier, i.e., a communication carrier ID as identification information to specify a communication carrier and supplies a communication carrier ID  207  to the control unit  108 . The detection unit  109  detects, from the reception signal, the communication carrier ID (the identifier of the communication carrier) of the service area where the portable terminal  1  currently is camping on (visiting) and supplies it to the control unit  108 . The control unit  108  compares the communication carrier ID from the detection unit  109  with the communication carrier ID  207  from the USIM  107 . If the communication carrier IDs match, the control unit  108  sends a control signal  208  to the T-SIR output unit  106 . 
     The T-SIR output unit  106  calculates a T-SIR  206  on the basis of the comparison result  205  from the comparison determination unit  105  and the control signal  208  from the control unit  108  and sends the T-SIR  206  to the inner loop control unit  11 . The T-SIR output unit  106  includes a T-SIR generation unit (target value generation unit)  106   a  and a T-SIR correction unit (target value correction unit)  106   b , as shown in  FIG. 3 . 
     The T-SIR generation unit  106   a  is the same as the conventional T-SIR generation unit  1106  shown in  FIG. 8  and generates a T-SIR on the basis of the comparison result  205  from the comparison determination unit  105 . That is, the T-SIR generation unit  106   a  generates a T-SIR in accordance with the actual reception quality in the portable terminal  1 . 
     The T-SIR correction unit  106   b  adds a correction value K to the T-SIR generated by the T-SIR generation unit  106   a  in response to the control signal  208  from the control unit  108  and sends the sum as the T-SIR  206  in inner loop control. In this arrangement, when the portable terminal  1  is camping on in the service area of a predetermined specific communication carrier, the T-SIR correction unit  106   b  adds the correction value K to the T-SIR generated by the T-SIR generation unit  106   a.    
     The operation of this embodiment will be described next with reference to  FIG. 4 . Referring to  FIG. 4 , “T” indicates the lower limit value of T-SIR, and “G” indicates the SIR limit value of the portable terminal  1 , as in  FIG. 9 . In a communication carrier with a strong reception field and a low reception BLER, the T-SIR drops to T as a result of long section reception quality measurement. When the portable terminal  1  is camping on in the service area of a specific communication carrier, the control unit  108  sends the control signal  208  to the T-SIR output unit  106  on the basis of the communication carrier ID  207  from the USIM  107 . The T-SIR output unit  106  adds the predetermined value K to the T-SIR and outputs a value (T+K) as the T-SIR  206 . 
     Even when the reception SIR abruptly deteriorates from time t 1 , it does not drop below the SIR limit value G of the portable terminal  1  from time t 2  because the T-SIR has increased by the predetermined value K. Hence, the portable terminal  1  can continuously receive the signal from the base station so that service interruption such as disconnection of speech communication can be prevented. 
     Another embodiment of the present invention will be described next with reference to  FIG. 5 . The same reference numerals as in  FIG. 2  denote the same constituent elements in  FIG. 5 . In a portable terminal according to this embodiment, the USIM  107  of the outer loop control unit in  FIG. 2  is omitted, and a storage unit  110  and a comparison determination unit  111  are added. Additionally, a control unit  108   a  and a detection unit  109   a  replace the control unit  108  and the detection unit  109  in  FIG. 2 , respectively. 
     As shown in  FIG. 6 , the detection unit  109   a  includes a cell information detection unit  109   b  and a signal level detection unit  109   c . The cell information detection unit  109   b  detects a base station ID from a demodulated signal as current cell information. The signal level detection unit  109   c  detects the signal level of the demodulated signal. In this embodiment, the signal level detection unit  109   c  detects a decrease in level of the demodulated signal. The base station ID detected by the cell information detection unit  109   b  and the decrease in level of the demodulated signal detected by the signal level detection unit  109   c  are supplied to the control unit  108   a , storage unit  110 , and comparison determination unit  111  as a detection signal  209 . 
     The control unit  108   a  includes a storage control unit  108   b  and a correction control unit  108   c , as shown in  FIG. 7 . The storage control unit  108   b  determines on the basis of the level decrease signal from the signal level detection unit  109   c  whether the reception SIR has abruptly deteriorated from a preset reference value. Upon determining that the reception SIR has abruptly deteriorated, the storage control unit  108   b  instructs to store, in the storage unit  110 , the base station ID detected by the cell information detection unit  109   b  and currently being received. The storage unit  110  sequentially stores the log of base station IDs corresponding to the timings of abrupt deterioration of reception SIR. 
     The comparison determination unit  111  compares base station IDs  211  stored in the storage unit  110  with the base station ID currently being received. If the base station IDs  211  include the base station ID currently being received, the comparison determination unit  111  sends a coincidence signal  212  to the control unit  108 . In response to the coincidence signal  212 , the correction control unit  108   c  of the control unit  108  sends a control signal  208  to a T-SIR output unit  106 . The T-SIR output unit  106  outputs the sum of the T-SIR and a predetermined value K, i.e., a value (T+K) as a T-SIR  206 . 
     As described above, in this embodiment, a base station which has exhibited abrupt deterioration of reception SIR under conditions of a strong reception field and a low reception BLER is stored. In the next utilization of this base station, the predetermined value K is added to the T-SIR. Hence, in this embodiment, even when no communication carrier information is obtained from the USIM  107 , the same effect as in the above-described embodiment can be obtained in the cell of the base station where the reception SIR has abruptly deteriorated formerly.