Radio terminal and radio communication method

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.

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.

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.