Hogil Kim Eun Jung Kim Ki Hwan Yum ROAL: A Randomly Ordered Activation and Layering Protocol for Ensuring K-Coverage in Wireless Sensor Networks. 43-52 2008 3 JNW 1 http://www.academypublisher.com/jnw/vol03/no01/jnw03014352.html db/journals/jnw/jnw3.html#KimKY08