Radio terminal and radio communication method

Abstract

A radio terminal according to a present invention comprising a communication judgment unit ( 131 ) configured to judge whether or not the direct communication with the radio base station is possible to continue; a message processor ( 132 ) configured to transmit an inquiry message inquiring whether or not a direct communication with the radio base station is possible, to a lower-level radio terminal in the tree structure network, when the continuation judgment unit judges that the direct communication with the radio base station is not possible to continue; and a master manager configured to register the lower-level radio terminal as an upper-level radio terminal in the tree structure network, upon receipt of a response message indicating that a direct communication with the radio base station is possible, from the lower-level radio terminal.

We claim: 
     
         1 . A radio terminal forming a tree structure network in which a radio terminal directly communicating with a radio base station is set to be a root, the radio terminal comprising:
 a direct communication unit configured to perform a direct communication with the radio base station;   a continuation judgment unit configured to judge whether or not the direct communication with the radio base station is possible to continue;   an inquiry message transmitter configured to transmit an inquiry message inquiring whether or not a direct communication with the radio base station is possible, to a lower-level radio terminal in the tree structure network, when the continuation judgment unit judges that the direct communication with the radio base station is not possible to continue; and   an upper-level terminal register configured to register the lower-level radio terminal as an upper-level radio terminal in the tree structure network, upon receipt of a response message indicating that a direct communication with the radio base station is possible, from the lower-level radio terminal.   
     
     
         2 . The radio terminal according to  claim 1 , further comprising:
 an instruction message transmitter configured to transmit an instruction message instructing the lower-level radio terminal to start a direct communication with the radio base station, upon receipt of the response message indicating that a direct communication with the radio base station is possible, from the lower-level radio terminal.   
     
     
         3 . The radio terminal according to  claim 1 , further comprising:
 an indirect communication unit configured to communicate with the radio base station via the upper-level radio terminal registered by the upper-level terminal register.   
     
     
         4 . The radio terminal according to  claim 1 , wherein the direct communication unit stops receiving a radio signal transmitted by the radio base station, when the lower-level radio terminal is registered as the upper-level radio terminal in the tree structure network by the upper-level terminal register. 
     
     
         5 . The radio terminal according to  claim 1 , further comprising:
 a reception quality measurement unit configured to measure a reception quality, which is a quality of a radio signal received from the radio base station; and   a threshold comparison unit configured to compare the reception quality measured by the reception quality measurement unit, with a threshold, wherein:   the continuation judgment unit judges that the direct communication with the radio base station is not possible to continue, when the reception quality is below the threshold.   
     
     
         6 . The radio terminal according to  claim 1  further comprising:
 a remaining battery charge amount detector configured to detect a remaining battery charge amount; and 
 a threshold comparison unit configured to compare the remaining battery charge amount detected by the remaining battery charge amount detector, with a threshold, wherein: 
 the continuation judgment unit judges that the direct communication with the radio base station is not possible to continue, when the remaining battery charge amount is below the threshold. 
 
     
     
         7 . The radio terminal according to  claim 1 , further comprising:
 a call restriction detector configured to detect a call restriction restricting the direct communication with the radio base station, wherein:   the continuation judgment unit judges that the direct communication with the radio base station is not possible to continue, when the call restriction is detected by the call restriction detector.   
     
     
         8 . A radio terminal forming a tree structure network in which a radio terminal directly communicating with a radio base station is set to be a root, the radio terminal comprising:
 an inquiry message receiver configured to receive an inquiry message inquiring whether or not a direct communication with the radio base station is possible, from an upper-level radio terminal in the tree structure network;   a communication judgment unit configured to judge whether or not a direct communication with the radio base station is possible, when the inquiry message receiver receives the inquiry message;   a direct communication unit configured to perform a direct communication with the radio base station, when the communication judgment unit judges that a direct communication with the radio base station is possible; and   a lower-level terminal register configured to register the upper-level radio terminal as a lower-level radio terminal in the tree structure network.   
     
     
         9 . The radio terminal according to  claim 8 , further comprising:
 a communication relay unit configured to relay a communication between the radio base station and the lower-level radio terminal registered by the lower-level terminal register.   
     
     
         10 . The radio terminal according to  claim 8 , further comprising:
 a response message transmitter configured to transmit a response message indicating that a direct communication with the radio base station is possible, to the upper-level radio terminal, when the communication judgment unit judges that a direct communication with the radio base station is possible; and   an instruction message receiver configured to receive an instruction message instructing the radio terminal to start a direct communication with the radio base station, from the upper-level radio terminal, wherein:   the direct communication unit performs a direct communication with the radio base station when the communication judgment unit judges that a direct communication with the radio base station is possible and the instruction message receiver receives the instruction message.   
     
     
         11 . The radio terminal according to  claim 8 , further comprising:
 an inquiry message transmitter configured to transmit the inquiry message to a lower-level radio terminal in the tree structure network when the communication judgment unit judges that a direct communication with the radio base station is not possible.   
     
     
         12 . A radio communication method used by a radio terminal forming a tree structure network in which a radio terminal directly communicating with a radio base station is set to be a root, the radio communication method comprising the steps of:
 performing a direct communication with the radio base station;   judging whether or not a direct communication with the radio base station is possible to continue;   transmitting an inquiry message inquiring whether or not a direct communication with the radio base station is possible, to a lower-level radio terminal in the tree structure network, when it is judged in the judging step that the direct communication with the radio base station is not possible to continue; and   registering the lower-level radio terminal as an upper-level radio terminal in the tree structure network, upon receipt of a response message indicating that a direct communication with the radio base station is possible, from the lower-level radio terminal.   
     
     
         13 . A radio communication method used by a radio terminal forming a tree structure network in which a radio terminal directly communicating with a radio base station is set to be a root, the radio communication method comprising the steps of:
 receiving an inquiry message inquiring whether or not a direct communication with the radio base station is possible, from an upper-level radio terminal in the tree structure network;   judging whether or not a direct communication with the radio base station is possible, when the inquiry message is received in the receiving step;   performing a direct communication with the radio base station when it is judged in the judging step that a direct communication with the radio base station is possible; and   registering the upper-level radio terminal as a lower-level radio terminal in the tree structure network, when it is judged in the judging step that a direct communication with the radio base station is possible.   
     
     
         14 . The radio terminal according to  claim 2 , further comprising:
 a reception quality measurement unit configured to measure a reception quality, which is a quality of a radio signal received from the radio base station; and   a threshold comparison unit configured to compare the reception quality measured by the reception quality measurement unit, with a threshold, wherein:   the continuation judgment unit judges that the direct communication with the radio base station is not possible to continue, when the reception quality is below the threshold.   
     
     
         15 . The radio terminal according to  claim 3 , further comprising:
 a reception quality measurement unit configured to measure a reception quality, which is a quality of a radio signal received from the radio base station; and   a threshold comparison unit configured to compare the reception quality measured by the reception quality measurement unit, with a threshold, wherein:   the continuation judgment unit judges that the direct communication with the radio base station is not possible to continue, when the reception quality is below the threshold.   
     
     
         16 . The radio terminal according to  claim 4 , further comprising:
 a reception quality measurement unit configured to measure a reception quality, which is a quality of a radio signal received from the radio base station; and   a threshold comparison unit configured to compare the reception quality measured by the reception quality measurement unit, with a threshold, wherein:   the continuation judgment unit judges that the direct communication with the radio base station is not possible to continue, when the reception quality is below the threshold.   
     
     
         17 . The radio terminal according to  claim 2 , further comprising:
 a remaining battery charge amount detector configured to detect a remaining battery charge amount; and   a threshold comparison unit configured to compare the remaining battery charge amount detected by the remaining battery charge amount detector, with a threshold, wherein:   the continuation judgment unit judges that the direct communication with the radio base station is not possible to continue, when the remaining battery charge amount is below the threshold.   
     
     
         18 . The radio terminal according to  claim 3 , further comprising:
 a remaining battery charge amount detector configured to detect a remaining battery charge amount; and   a threshold comparison unit configured to compare the remaining battery charge amount detected by the remaining battery charge amount detector, with a threshold, wherein:   the continuation judgment unit judges that the direct communication with the radio base station is not possible to continue, when the remaining battery charge amount is below the threshold.   
     
     
         19 . The radio terminal according to  claim 4 , further comprising:
 a remaining battery charge amount detector configured to detect a remaining battery charge amount; and   a threshold comparison unit configured to compare the remaining battery charge amount detected by the remaining battery charge amount detector, with a threshold, wherein:   the continuation judgment unit judges that the direct communication with the radio base station is not possible to continue, when the remaining battery charge amount is below the threshold.   
     
     
         20 . The radio terminal according to  claim 2 , further comprising:
 a call restriction detector configured to detect a call restriction restricting the direct communication with the radio base station, wherein:   the continuation judgment unit judges that the direct communication with the radio base station is not possible to continue, when the call restriction is detected by the call restriction detector.   
     
     
         21 . The radio terminal according to  claim 3 , further comprising:
 a call restriction detector configured to detect a call restriction restricting the direct communication with the radio base station, wherein:   the continuation judgment unit judges that the direct communication with the radio base station is not possible to continue, when the call restriction is detected by the call restriction detector.   
     
     
         22 . The radio terminal according to  claim 4 , further comprising:
 a call restriction detector configured to detect a call restriction restricting the direct communication with the radio base station, wherein:   the continuation judgment unit judges that the direct communication with the radio base station is not possible to continue, when the call restriction is detected by the call restriction detector.