  Characterizing and comparing the optimal energy efficiency in energy-aware
machine-to-machine (M2M) random access networks remains a challenge due to the
distributed nature of the access behavior of nodes. To address this issue, this
letter focuses on the energy efficiency limits of two typical random access
schemes, i.e., connection-based Aloha and packet-based Aloha, based on which we
conducted a performance comparison. Specifically, by integrating limited energy
constraints and network throughput, the lifetime throughput can be derived, and
further optimized with a guarantee of targeted lifetime via selecting the
transmission probability. Then we present a comparative study on the optimal
lifetime throughput of packet-based Aloha and connection-based Aloha to
characterize criteria for beneficial connection establishment.
