Wireless Sensor and Actuator Networks: Algorithms and Protocols for Scalable Coordination and Data Communication

1.6 ADJUSTABLE TRANSMISSION RANGE AND POWER METRIC

Sensor nodes have the capacity to adjust their transmission ranges without incurring any significant cost for the adjustment. A common transmission radius is normally preferred because medium access protocols currently considered to be de facto standards, such as Zibgee, require it for proper functioning. However, finding a minimal common transmission radius is a nontrivial problem, especially for its maintenance. A possible compromise is that each sensor is made aware of its neighbors by using “hello” messages. But when the neighbor for forwarding is decided, the transmission power could be adjusted to reflect the distance. Here, we still assume the UDG modeling with adjusted transmission radius. In reality, there is an impact of the realistic physical layer at critical transmission distances, which will be discussed later.

A simple power consumption model is introduced in Rodoplu and Meng (1999). The total power needed to transmit and receive a message between two nodes at distance d is proportional to d^α + c, where α is the signal strength attenuation factor which is normally between 2 and 5 depending on the transmission medium and the environment, and c is a contact that accounts for signal processing at the transmitter and receiver, as well as the minimal power to receive a signal properly. This model has been restated in Heinzelman et al. (2000). The energy consumption per bit is calculated as follows: power = E_trans +