A Comprehensive Analysis of the MAC Unreliability Problem in 802.15.4 Wireless Sensor Networks

摘要

Wireless Sensor Networks (WSNs) represent a verypromising solution in the field of wireless technologies for industrialapplications. However, for a credible deployment of WSNs inan industrial environment, four main properties need to be fulfilled,i.e., energy efficiency, scalability, reliability, and timeliness.In this paper, we focus on IEEE 802.15.4 WSNs and show thatthey can suffer from a serious unreliability problem. This problemarises whenever the power management mechanism is enabled forenergy efficiency, and results in a very low packet delivery ratio,also when the number of sensor nodes in the network is very low(e.g., 5).We carried out an extensive analysis—based on both simulationand experiments on a real WSN—to investigate the fundamentalreasons of this problem, and we found that it is causedby the contention-based Medium Access Control (MAC) protocolused for channel access and its default parameter values. We alsofound that, with a more appropriate MAC parameters setting, itis possible to mitigate the problem and achieve a delivery ratio upto 100%, at least in the scenarios considered in this paper. However,this improvement in communication reliability is achieved atthe cost of an increased latency, which may not be acceptable forindustrial applications with stringent timing requirements. In addition,in some cases this is possible only by choosing MAC parametervalues formally not allowed by the standard.