Distributed networks of wireless sensors/actuators will enable the reliable monitoring and intelligent control of the physical environment accomplishing different tasks ranging from space monitoring and surveillance to homeland security without human intervention. Motivated by the observation that many of these applications are safety critical and have hard real-time requirements, this paper focuses on the problem of providing delay and throughput guarantee to real-time messages in wireless sensor networks. It extends the cellular structure in [4] and analyzes the sensor network capacity when messages are scheduled with the Implicit-EDF algorithm.