Cluster head assisted method for converting user terminal from D2D communication to cellular communication

A cluster head assisted method for converting a user terminal from device-to-device (D2D) communication to cellular communication, comprising following steps:

• Step 1:
• determining of the quality of a D2D link between a user terminal and a cluster head is lower than a predetermined threshold, the user terminal performing cell search and a random access process to access a cellular network;
• and
• Step 2:
• the user terminal sending a switching request to the cluster head through a D2D link, wherein the switching request comprises an ID of a target base station to which the user terminal is going to access;
• and
• the cluster head sending the switching request to a serving base station through a cellular link,
• wherein the ID of the target base station to which the user terminal is going to access is the same as an ID of the serving base station where the cluster head belongs, indicating that the target base station to which the user terminal is going to access and the serving base station where the cluster head belongs are the same base station, the user terminal accesses the serving base station where the cluster head belongs, and establishes a radio resource control (RRC) connection with the serving base station;
• the serving base station replies a switching response message to the cluster head through the cellular link;
• and
• the cluster head sends switching response information to the user terminal through the D2D link;
• and
• determining of the ID of the target base station to which the user terminal is going to access is different from an ID of the serving base station where the cluster head belongs, the user terminal accesses the target base station, and establishes an RRC connection with the target base station;
• the serving base station forwards the switching request of the user terminal to the target base station, and the target base station replies a switching response message to the serving base station.