In this article, network cooperation as a means of energy saving in green radio communications is investigated. For the system model with overlapped coverage from different networks, the proposed technique can achieve energy saving without increasing transmission power. It relies on cooperation among different networks to save energy on two scales. On a large scale, networks with overlapped coverage alternately switch their BSs on and off according to the long-term fluctuations in traffic load. On a small scale, each active BS switches its channels on and off according to the short-term fluctuations in traffic load. Numerical results demonstrate satisfactory service quality in terms of call blocking probability and a large percentage of energy saving for each network. In the proposed framework, the service quality constraints can be extended to include metrics other than call blocking probability, such as the minimum achieved throughput for data applications, and delay and delay jitter for video streaming applications.