On the other hand, service providers can take advantage of network cooperation to enhance network performance. Multiple heterogeneous networks can cooperate to provide a multihop backhaul connection in a relay manner. This can increase the coverage area of such networks. Moreover, cooperation among different networks can provide load balancing among these networks. As a result, traffic overload situations in one network can be avoided. Also, network cooperation can be exploited to save energy in green radio communications. For geographical regions where two or more networks have overlapped coverage, cooperation among the networks can achieve energy saving and avoid the dynamic planning shortcoming. Such networks can alternately switch on and off their resources according to the traffic load conditions, and the traffic is carried on by the remaining active resources. In such a case, an optimal resource on-off switching framework is required to adapt the available resources to the traffic load fluctuations and to maximize the amount of energy saving under service quality constraints.