Interference-fault free transmission schedule in tree-structured WSN

Abstract

Interference due to concurrent link transmissions has for long been recognized as a major cause for issues like packet retransmissions, distorted signal strength and communication link failures in WSN. The two best known approaches to model interference, namely the Protocol Interference (PrI) and Physical Interference models, fail to identify all Potential Interferers (PIs) to a given link. Therefore, the two models have limited utility in determining an Interference-Fault Free Transmission (IFFT) schedule for all active links in the network. This leads to serious repercussions, especially in tree-structured WSNs, where data aggregation is hierarchical. In a pioneering work done earlier, we have developed Composite Interference Mapping (CIM) model, which succeeds in identifying the PIs of all active links in a network. In this paper, we implement the CIM model to map PIs of all transmission links in a tree-structured WSN. We develop an IFFT-Tree algorithm to obtain an IFFT schedule for all links in an aggregation tree, and analytically prove that the algorithm is both optimal and complete. To support our analytical studies, we implement the IFFT-Tree algorithm and carry out extensive simulations to show that the algorithm minimizes the number of time slots required to schedule all active links. We introduce three new performance metrics to study the performance of IFFT-Tree algorithm, and to compare the efficacy of the CIM model with PrI model. The results of the simulations prove that the PrI model identifies only a small subset of total PIs identified by the CIM model. This finding highlights the threat to the credibility of data being aggregated along the tree, if interference-faults arising due to PIs which are not identified by the PrI model, proliferate into the tree-structured WSN.