  Machine-to-Machine (M2M) communications is one of the key enablers of the
Internet of Things (IoT). Billions of devices are expected to be deployed in
the next future for novel M2M applications demanding ubiquitous access and
global connectivity. In order to cope with the massive number of machines,
there is a need for new techniques to coordinate the access and allocate the
resources. Although the majority of the proposed solutions are focused on the
adaptation of the traditional cellular networks to the M2M traffic patterns,
novel approaches based on the direct communication among nearby devices may
represent an effective way to avoid access congestion and cell overload. In
this paper, we propose a new strategy inspired by the classical Trunked Radio
Systems (TRS), exploiting the Device-to-Device (D2D) connectivity between
cellular users and Machine-Type Devices (MTDs). The aggregation of the locally
generated packets is performed by a user device, which aggregates the
machine-type data, supplements it with its own data and transmits all of them
to the Base Station. We observe a fundamental trade-off between latency and the
transmit power needed to deliver the aggregate traffic, in a sense that lower
latency requires increase in the transmit power.
