A heterogeneous network includes a first base station, a number of second base stations and a mobile device. The mobile device communicates with the second base stations via mm-wave signals and send, via wireless signals, the first base station a position of the mobile device and a request for connecting with one of the second base stations. The first base station determines one of the second base stations to connect with the mobile device according to the position and the request sent by the mobile device. The first base station sends, via the wireless signals, the mobile device a first beam angle information and triggers the mobile device and the one determined second base station to perform a beam training process according to the first beam angle information.