A critical issue in wireless sensor networks isrepresented by the limited availability of energy withinsensor nodes. An effective approach for energy conservationis scheduling sleep intervals for extraneous nodes, while theremaining nodes stay active to provide continuous service.Most previous solutions assumed a perfect radio conditionwith a static, circular coverage. However, in real situations,radio signals are very dynamic and irregular in theircoverage. This is especially true for wireless sensornetworks, which usually employ low quality radio modulesto reduce the cost. Assuming no location information isavailable, we approach the problem in this paper from twoaspects: space and time. We present a topology controlalgorithm, termed OTC, for sensor networks withconsideration of radio irregularity and dynamic radiocoverage. It uses two-hop neighborhood information to selecta subset of nodes to be active among all nodes in theneighborhood. Each node in the network selects its own setof active neighbors from among its one-hop neighbors. Thisset is determined such that it covers all two-hop nodes. OTCis evaluated against a well-known algorithm from theliterature, namely Span through realistic simulations usingTOSSIM. The results show that under dense deploymentand irregular and dynamic radio coverage, our algorithmoutperforms Span.