Question 1

Consider a wireless sensor network consisting of a sink and 10 clusters of 8 sensors plus a cluster head each. In this question and its sequel, we will consider the energy consumed by the transmission subsystem (i.e., we will not include the energy consumed in sensing and processing). Sensors send their information to the cluster head in 100-bit frames. The cluster head aggregates the information received and sends it to the sink in 100-bit frames. Consider the following values:

It takes 1 microJ per bit for a sensor to transmit to its designated cluster head;

It takes 10 microJ per bit for a cluster head to transmit to the sink;

It takes 0.5 microJ per bit to receive.

Suppose sensors are time-coordinated somehow and during each time slot half of the sensors transmit data to their respective cluster heads. The cluster heads aggregate the data and each cluster head transmits a single frame to the sink. (All of this happens during a single time slot.) What is the energy consumed by the network (including all sensors and cluster heads) during each time slot? Express your answer in mJ (milliJoules):

Answer: mJ.

Question 2

Consider the same set up as Question 1, but now in each time slot only one sensor in each cluster transmits a frame to its cluster head. The cluster heads aggregate the information received and transmit the result to the sink in a single frame every other time slot. What is the average energy consumed by the network (including all sensors and cluster heads) per time slot, measured in mJ?

Answer: mJ.