Patent ID: 9008649
Filing Date: 2015-04-14
Classification: H04W

Abstract:
1. A first radio terminal configured to communicate in a tree structure network in which a radio terminal directly communicating with a radio base station is set to be a root, the first radio terminal being configured as a root radio terminal and 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 to a lower-level second radio terminal in the tree structure network an inquiry message inquiring whether or not a direct communication with the radio base station is possible by the second radio terminal to determine whether the second radio terminal can become a new root radio terminal, when the continuation judgment unit judges that the first radio terminal can no longer directly communicate with the radio base station; and an upper-level terminal register, wherein upon receipt of a response message from the second radio terminal indicating that direct communication with the radio base station is possible, the upper-level terminal register registers the second radio terminal as an upper-level radio terminal in the tree structure network, wherein the second radio terminal becomes the new root radio terminal that directly communicates with the radio base station and replaces the first radio terminal as the root radio terminal, wherein the continuation judgment unit determines whether or not direct communication with the radio base station is possible to continue by determining whether a reception level of a radio signal received form the radio base station is stable.