LTE-direct vs. WiFi-direct for machine-type communications over LTE-A systems

Current and future releases of 3GPP standards will include enhancements in LTE-Advanced for machine-type communications (MTC). The main reason for this new trend is the fact that 5G wireless systems will need to enable the coexistence between MTC and human-type communications (HTC). Therefore, novel solutions are needed to efficiently exploit the radio resources for MTC, considering, among others, the need to optimize transmissions for small data packets. With this aim, this paper addresses the use of short-range device-to-device (D2D) communications as enabling technology to efficiently manage the radio spectrum and to reduce the energy consumption of MTC devices. We consider a scenario where MTC devices are grouped in a cluster; among the cluster members, one terminal acts as aggregator in charge for (i) receiving data from neighboring terminals via D2D links and (ii) relaying the aggregated data to the base station via macro-cellular link. The main contribution of this paper is to compare the performances of the two most popular D2D technologies, i.e., WiFi-Direct and LTE-Direct, used to transmit data toward the aggregator. The performance evaluation in terms of latency and energy efficiency has been conducted in a wide set of scenarios by varying the number of clustered devices and the data to upload per single MTC device.