Energy analysis of cooperative and duty-cycled systems in shadowed environments

We assume a traditional three-node cooperative model where a source directly communicates with a sink unless in outage, in which case it reverts to a relay to facilitate communications. In contrast to prior art, however, we focus on ultra-low power wireless sensor and machine-to-machine networks, such as standardised through the emerging IEEE 802.15.4e medium access control (MAC). This requires to cater for a more realistic link layer by incorporating shadowing, retransmissions and a duty cycled system where nodes wake up according to a given schedule. The thus designed protocol is referred to as Cooperative and Duty-Cycled Automatic Repeat Request (CDC-ARQ), and thoroughly analysed in this paper. Notably, we quantify the energy consumption of the CDC-ARQ scheme and establish optimal operating regions to minimize energy expenditure for the overall system.