Optimizing Physical Layer Energy Consumption for Reliable Communication in Multi-hop Wireless Sensor Networks

Developing energy efficiency protocols to optimize the energy consumption is most important for lifetime of Wireless Sensor Networks. We consider multi hop WSNs whose lifetime is critically dependent upon the rate of energy consumption of the battery of various constituent sensor nodes. Objectives: Our objective is to develop a cross layer energy efficient protocol which optimizes energy consumption of the sensor nodes at the Network, MAC and Physical layers of the protocol stack as most of energy consuming factors exist in these three layers. But, in this paper we focus only on optimizing physical layer in terms of energy consumption for WSNs. Methods/Analysis: We define and implement a mathematical model for the physical layer of Wireless Sensor networks in MATLAB. Our objective is to study the transmission energy only, so we do not consider other factors such as buffer overflows, link congestions etc. We assume that each link in the network has infinite large transmit buffer. We also assume that all nodes receive signals of same strength; hence the bit error rate is same for all links. To study these tradeoffs, we implement total transmission energy per packet against varying number of nodes (for different values of link errors). Findings: The results show that for lower values of the link error rates, the large number of short range hop nodes leads to a significant reduction in the total energy consumption. However, when this number of nodes tends to surpass the optimal value, error rates becomes higher and potential power savings due to the introduction of large number of intermediate node are negated by a sharp increase in effective bit error rate. Novelty of the Study: Traditionally, the problem of energy consumption optimization is considered separately at different layers of the protocol stack. We propose a cross layer energy efficient protocol which optimizes energy consumption of the sensor nodes at the Network, MAC and Physical layers of the protocol stack simultaneously. Conclusion: Choosing a communication path having large number of short hop nodes over a path having less number of long hop nodes leads to a significant reduction in the total energy consumption and a comprehensive, cross layered scheme of energy optimization is better approach to cope with the problem of energy consumption.