DF versus AF: Energy consumption comparison for IEEE 802.15.4 networks

IEEE 802.15.4 refers to a standard meant for short range wireless sensor networks (WSNs). Recently, the standard has gained huge popularity due to its simplicity, scalability, and low power consumption. In this paper, we investigate the energy efficiency of relay assisted dual hop communication between two 802.15.4 compliant wireless nodes. Novel energy consumption models for both amplify-and-forward (AF) and decode-and-forward (DF) selective relaying protocols have been formulated and energy efficiency of these two protocols have been assessed by comparing the respective energy requirement per successful bit transmission. Small scale fading introduces outage during transmission over 802.15.4 links. The results show that although under moderate to high channel outage probability, DF relaying offers better energy efficiency than AF relays, when the outage is low, their performances become identical. Next, variation of energy consumption with data payload size is elaborated for both DF and AF relays. It was found that, under moderate outage, there exists an optimum value for the payload size where energy saving is maximum. For similar channel conditions, the optimum payload size is more for DF relays. When the outage value is very high energy consumption increases exponentially with payload size. The trend reverses when the outage is low.