Communication system using base station clusters

A communication system using a cluster of base stations, including multiple base stations set in a service area. The multiple base stations establish multiple clusters, and signal coverage of the multiple clusters fills the service area. The first base station and its first adjacent base station of the multiple base stations belong to a first cluster of the multiple clusters. A coverage area of the first base station partially overlaps with a coverage area of the first adjacent base station. In response to the first base station satisfies a power-saving condition, the first base station activates a deep sleep mode.