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Wide range of applications such as disaster management, military and security have fueled the interest in sensor networks during the past few years. Sensors are typically capable of wireless communication and are significantly constrained in the amount of available resources such as energy, storage and computation. Such constraints make the design and operation of sensor networks considerably different from contemporary wireless networks, and necessitate the development of resource conscious protocols and management techniques. In this paper we present an energy efficient, scalable and collision free MAC layer protocol for sensor networks. The approach promotes time-based arbitration of medium access to limit signal interference among the transmission of sensors. Transmission and reception time slots are prescheduled to allow sensors to turn their radio circuitry off when not engaged. In addition, energy consumption due to active to sleep mode transitions is minimized through the assignment of contiguous transmission/reception slots to each sensor. Scalability of the approach is supported through grouping of sensors into clusters. We describe an optimization algorithm for energy conscious scheduling of time slots that prevents intra-cluster collisions and eliminates packet drop due to buffer size limitations. In addition, we also propose an arbitration scheme that prevents collisions among the transmission of sensors in different clusters. The impact of our approach on the network performance is qualified through simulation. . A sensor network consists of minute devices that are capable of probing the environment and reporting the collected data, typically using a radio, to the command center. Sensor networks can serve many civil and military applications such as disaster management, combat field surveillance and security. In such applications, the sensors are usually powered using small batteries and replacing sensor's battery is not possible or not practical. Such energy constraints limit sensors' lifetime and thus make efficient design and management of sensor networks a real challenge. Therefore, a lot of the research related to sensor networks has focused on energy-awareness and minimization [1] [7][8]. In this paper we concentrate on the minimization of energy consumption at the MAC layer through time-based arbitration of the sensor's medium access.Medium access is a major consumer of sensor energy, especially for long-range transmission and when the radio receiver is kept on all the time. Energy consumed for radio transmission is directly proportional to distance squared and can significantly magnify in a noisy environment. Energy-aware routing typically pursues multi-hop paths in order to optimize the transmission energy [9][10]. On the other hand, time-based medium access control (MAC) saves transmission energy by limiting the potential for collisions and minimizes the energy consumed in the receiver by turning the radio off when it is idle [11] [12]. Generally, an efficient MAC layer protocol...

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