Gen3: protocolo MAC adaptativo escalonado com multiplexação estatística

Abstract

Wireless Sensor Networks (WSNs) have been subject of development and study for more than a decade. With the development of more robust devices that integrate more resources, proposals for using RSSF have passed from applications with high fault tolerance to control and monitoring applications that require high availability and reliability. Medium Access Control (MAC) protocols play a key role in these networks, enabling them to operate reliably and efficiently. MAC protocols can be classified as Contention-Based Protocols (CBP) or scheduled protocols (TDMA - Time Division Multiple Access). CBP protocols present low delivery latency compared to TDMA protocols in low traffic conditions. Under high traffic or high node densities, however, CPB protocols present unpredictable operation, with higher packet losses and increased latency compared to TDMA protocols. Although they present a more stable behavior over CBP protocols when submitted to heavy traffic, TDMA protocols may underutilize the medium in low traffic conditions or when nodes present unbalanced traffic generation. If in a TDMA network a node generates few packets and another one generates a high amount of packets, the time allocated to each node remains equal, being underutilized by the first node and potentially insufficient for the second. The use of statistical multiplexing in TDMA protocols can attenuate this problem by allowing the opportunistic usage of underutilized slots. Another issue to consider is the mobility and network adaptation to different conditions. In general, TDMA protocols maintain information about the network that vary with topology and node movement. Some protocols define parameters based on expected network characteristics, which may eventualy limit nodes operation or even their association to the network. This work presents Gen3, a generalist TDMA MAC protocol that organizes the network logically as a tree. The protocol is autoconfigurable and adaptive to the number of nodes in the network while maintaining the operation of already associated nodes. By using multiple channels, it allows collision-free concurrent communcations to increase throughput, delivery rate, and reduce packet latency. In addition, a statistical multiplexing mechanism allows the opportunistic use of an underutilized slot by nodes that have higher demand for medium access. Gen3 was evaluated through exhaustive simulations using OMNeT++ simulator and INET framework. Results show its capacity to offer high delivery rates and high throughput, even when submitted to intense traffic, achieving higher performance than the protocol used for comparison. Protocol’s adaptability could be evaluated by its correct configuration in different topologies and by the reduced impact of node mobility in packet transmission metrics.