# NB-IoT for D2D-Enhanced Content Uploading with Social Trustworthiness in 5G Systems
## 3 NB-IoT and D2D Communications in the 5G Era  
The upcoming fifth generation (5G) wireless systems are being considered as the best candidate to allow effective interworking of IoT devices, thanks to the benefits these offer in terms of enhanced coverage, high data rate, low latency, low cost per bit, and high spectrum efficiency. There is a general consensus among academia and industries that 5G will have a huge impact in three main areas of communication: (1) enhanced mobile broadband (eMBB); (2) massive-machine type communication (M-MTC); and (3) critical-MTC (c-MTC). In particular, these three areas have different requirements and applications. Nevertheless, those are not standalone use cases, but may overlap in some cases. In our work, we take into consideration a use case that is somehow in the middle between c-MTC and M-MTC. We may think of process automation within a factory or other similar scenarios. In these cases, available and reliable connections for monitoring and diagnosis of a high number of industrial elements (i.e., M-MTC) are the most important. Nevertheless, even if the measured values from the sensors change relatively slowly, it is still important to have reasonable latency (e.g., from 20 to 50 ms) in order to react in a timely manner to an issue that can occur on the way (e.g., c-MTC). With reference to typical machine-type communications (MTC), the Third Generation Partnership Project (3 GPP) has introduced novel features [26] that better support the intrinsic battery-constrained capabilities of IoT devices and the typical small data packets over licensed bands (e.g., LTE). In September 2015, 3 GPP standardized _narrowband IoT (NB-IOT)_, a new narrowband radio technology to address the requirements of the Internet of things (IoT). This new technology provides improved indoor coverage, support of massive number of low throughput devices, has low delay sensitivity, ultra-low device cost, low device power consumption and an optimized network architecture. At the time we are writing this paper, a first release of NB-IoT had been completed by 3 GPP. However, the standardization process is still ongoing and further enhancements and new features are expected in 3 GPP Release 14 (updated according to the last 3 GPP meetings) and Release 15. Further, NB-IoT is expected to be released in a form of a software update for the network operators and is fully backward compatible with existing 3 GPP devices and infrastructure. In particular, given an available bandwidth of around 200 kHz for both downlink and uplink, the air interface of NB-IoT is optimized to ensure harmonious coexistence with LTE. In particular, the technology can be deployed \"in-band\" using the resource blocks within a normal LTE carrier (an LTE operator can deploy NB-IoT inside an LTE carrier by allocating one of the physical resource blocks (PRB) of 180 kHz to NB-IoT), or in the unused resource blocks within a LTE carrier guard-band (for instance, for an LTE bandwidth of 10 MHz (i.e., 56 resource blocks--RBs), 6 RBs are reserved for guard subcarriers and can be used for NB-IoT), or in \"standalone\" manner for deployments in dedicated spectrum [27]. Thanks to this latter feature whereby NB-IoT may be deployed as a stand-alone carrier using any available spectrum exceeding 180 kHz, a Global System for Mobile Communications (GSM) operator can also replace a GSM carrier (200 kHz) with NB-IoT. As reported in the white paper from Nokia [11], the maximum data rates (i.e., by considering the overall bandwidth) in terms of instantaneous peak rates provided by the NB-IoT technology are: _170 kbps (Downlink - DL)_ and _250 kbps (Uplink - UL)_. To enable the allocation of small portions of bandwidth, NB-IoT uses tones or subcarriers instead of resource blocks. The subcarrier bandwidth for NB-IoT is 15 kHz (or 3.75 kHz in some cases), compared with a resource block, which has an effective bandwidth of 180 kHz. Furthermore, the data rates available for the single tone in downlink and uplink are 680 bits and 1000 bits, respectively.