# NB-IoT for D2D-Enhanced Content Uploading with Social Trustworthiness in 5G Systems
## 3 NB-IoT and D2D Communications in the 5G Era
These values will satisfy most of the communication requirements for IoT-based services where very small data packets are usually transferred. Another form of technology which has gained high momentum in the evolution towards 5G systems is D2D communication where devices communicate directly over cellular resources or Wi-Fi/Bluetooth technologies without routing the data over a base station (BS) or an access point (AP). Recent studies showed how D2D communications may find important applications in IoT/5G integration [6; 7]. Indeed, D2D communications not only allow for extending the coverage and overcoming the limitations of conventional cellular systems, but they represent a fertile ground for use cases and services (e.g., social interactions and gaming, local information exchange, etc.). For instance two users can find each other whenever in proximity and share data or play interactive games. Moreover, social applications, public safety and emergency handling may benefit from D2D communications as devices can provide local connectivity in case of damage to the network infrastructure. Other fields of applications may be vehicle-to-vehicle (V2V) communication in intelligent traffic systems (ITS) where D2D communications can be exploited for traffic control/safety applications among others. Several works in the recent literature have investigated the benefits D2D communications can introduce, making it a very appealing solution for the exacting requirements of IoT emerging 5G network scenarios [28; 29]. The most important of these benefits are [30]: (1) higher data rate in the communications; (2) reliability in the communications including in the case of network failure; (3) energy savings due to lower transmission power levels for devices in proximity; (4) reduced number of cellular connections (known as traffic offloading); and (5) possibility for instantaneous communications between devices. In this paper, the potential benefits of NB-IoT and D2D communications are jointly exploited for cooperative content uploading from a set of devices to the cellular base station, through short-range multihop relaying. In particular, NB-IoT is exploited for radio links between users and the eNodeB, whereas proximity-based transmissions (i.e., D2D) are established among devices in mutual proximity. However, a necessary condition for such a \"cooperative\" relaying solution to bring benefits compared to the \"non-cooperative\" case, is that the link quality of the multihop D2D channels is higher than the one of the separate links to the Internet. This condition is more likely to occur in non-isotropic propagation environments with obstacles where non-line-of-sight (NLOS) conditions may cause partial and temporary out-of-coverage conditions, as is the case of the Internet of vehicles, an instance of the IoT where objects are represented by cars [31]. The content we have in mind for the devices in the scenario is small data coming for instance from sensing activities, security or monitoring applications with limited amount of data to transmit, typical of IoT applications. NB-IoT is, in fact, not thought of for bandwidth-hungry applications, e.g., videos, or big file transmissions. Currently IoT devices are equipped with a wide range of radio technologies. For instance, Pycom ([[https://www.pycom.io/](https://www.pycom.io/)]([https://www.pycom.io/](https://www.pycom.io/))) provides some shields for IoT applications that include both long- and short-range connectivity such as LoRa, LTE, NB-IoT, Bluetooth, and LTE Cat-M1. The idea we want to investigate is to offload the part of the traffic that cannot be handled entirely by NB-IoT via short-range links over the D2D technology.