Device to device (D2D) is increasingly becoming a prominent technology within the 5G story, portrayed as a means of offloading traffic from the core network. The ever increasing demand for vehicular traffic consumption is providing the impetus for a new architectural design that can harness the benefits of Device to device (D2D) for vehicular users, taking a step toward offloading vehicular traffic from the core network.

 The D2D design aspects apply to V2V communication:

Communication environment: The communication environment in V2V is quite different than in D2D due to the high mobility of the vehicles. Thus, network connectivity may play a more important role in vehicular communications, compared with system throughput. These characteristics can significantly affect D2D resource allocation strategies and system performance, and thus should be re-examined for V2V.

Scheduling mechanisms envisioned for D2D communications can be used for vehicular communications, but to accommodate these mechanisms in vehicular systems is a not a trivial task. Both uplink and downlink channels must be taken into account while applying D2D scheduling mechanisms to vehicular applications. For the uplink, efficient schedulers must be developed to avoid congestion in crowded networks. For the downlink, a new cross-layer based scheduling is needed in LTE-A to cope with vehicular applications. This can be done by designing a new efficient LTE-A QoS class scheduler [1].

Control plan latency is the time required to perform the transitions between different LTE states. A D2D in LTE is always in one of three states: connected (active), idle, or dormant (battery saving mode). 3GPP specifies that the transition time from the idle state to the connected state should be less than 100 ms, excluding downlink paging and non-access stratum (NAS) signaling delay. Furthermore, it is specified that the transition time from the dormant state to the connected state should take less than 50 ms. Similarly, one way user plan latency in D2D is approximately 5 ms. These latency requirements should be re-redesigned for more strike constraint in the context of vehicular communication where safety applications require every vehicle to transmit a periodic safety message.

Standardization bodies, e.g. ETSI ITS, must rectify their presently available standards along with architectures to enable D2D to support onboard vehicular applications that provide the impetus for road safety and intelligent vehicular systems.

Economic issues should also be considered when deploying D2D mechanisms onto vehicular applications, because D2D uses licensed spectrum which is not free of charge while exchanging data among the vehicles’ owners. Therefore, new business models compatible with market pricing must be envisioned.

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Reference
[1] G. Araniti et al., “LTE for Vehicular Networking: A Survey,” IEEE Commun. Mag., vol. 51, no. 5, May 2013, pp. 148–57.