Because of hidden-node problem, the interference range is larger than the transmission range in wireless communications. In Figure 2(a), shows that even though the transmission radius of nodes n1 and n3 do not overlap, collision still occurs at the receiver (node S) when CC-5013 they transmit at the same time. When collision occurs, retransmission is required to ensure the data is successfully Inhibitors,Modulators,Libraries received. These retransmissions incur additional energy consumption, which will jeopardize the advantages of data aggregation. Data retransmission times are determined by the total number of sensor nodes whose transmission radius covers the receiver (or equivalent to the total number of sensor nodes within each other��s interference range). In other words, the more flows are aggregated, the higher the probability that the senders will incur data retransmission.

Hence, there is a tradeoff between data aggregation and retransmission. Good Inhibitors,Modulators,Libraries data aggregation tree should address data aggregation and MAC layer retransmission Inhibitors,Modulators,Libraries at the same time.Figure 2.Tradeoff between retransmission and data aggregation.Figure 2 gives an illustrative example to show the tradeoff between the data aggregation and retransmission, where nodes n1, n2, and n3 are the data source nodes. Without considering data collision, the optimal aggregation tree is as shown in Figure 2(a). Note that when an intermediate node aggregates more data, a greater number of collisions would occur at the intermediate nodes, which results in additional energy consumption. Node S, the receiver of the three children nodes, will suffer significant collisions that results in more retransmission times.

With considered collision effects, a more energy efficient data aggregation tree is as shown in Figure 2(b). In this figure, by reducing Inhibitors,Modulators,Libraries the transmission radius of node n1, and change its routing assignment to node n4, the total energy consumption could be reduced. Even though there is extra energy consumption at node n4, there are only two children nodes at node S, and thus, the retransmission times caused by collision could be significantly reduced. Hence, the energy consumption associated with retransmission from collisions should be carefully addressed in WSN. This example also shows that a good tradeoff between data aggregation and retransmission is facilitated by intelligent transmission radius and routing assignments.

The energy consumption function (including transmission power and retransmission AV-951 power), as shown in Figure 2, is calculated by its objective function (IP), as described Tofacitinib in Section 3.This paper discusses the impacts of retransmission on data aggregation, and proposes a MAC aware energy efficient data aggregation algorithm to consider a tradeoff between the benefits of data aggregating and data retransmission costs in WSN. To the best of our knowledge, there is no literature that addresses the cross-layer (layer 2 and layer 3) MAC aware data aggregation routing algorithm in WSNs.