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Coverage preservation and prolonging lifetime are the fundamental issues in wireless sensor networks. Due to the large variety of applications, coverage is subject to a wide range of interpretations. Some applications require that every point in the area is monitored by only one sensor while other applications may require that each point is covered by at least k sensors (k> 1) to achieve fault tolerance. Hence, it is desirable to activate a minimum number of sensors that are able to ensure coverage area and turn off some redundant sensors to save energy and therefore extend network lifetime. Furthermore, determining a minimum number of active sensors is based on the degree coverage required and its level. In this paper, we propose a cluster-based efficient-energy coverage scheme called CSA_VS (Cluster-based Scheduling Algorithm–Virtual Sensor) to ensure the full coverage of a monitored area while saving energy. CSA_VS uses a novel sensor-scheduling scheme based on the k-density and the remaining energy of each sensor to determine the state of all the deployed sensors to be either active or sleep as well as the state durations. Simulation results showed that CSA_VS provides better performance in terms of the number and the percentage of active sensors to guarantee the area coverage compared to other algorithms.