text: In the next generation cellular networks, device-to-device (D2D) communication is already considered a fundamental feature. A problem of multi-hop D2D networks is on how to define forwarding algorithms that achieve, at the same time, high delivery ratio and low network overhead. In this paper we aim to understand group meetings' properties by looking at their structure and regularity with the final goal of applying such knowledge in the design of a forwarding algorithm for D2D multi-hop networks. We introduce a forwarding protocol, namely GROUPS-NET, which is aware of social group meetings and their evolution over time. Our algorithm is parameter-calibration free and does not require any knowledge about the social network structure of the system. In particular, different from the state of the art algorithms, GROUPS-NET does not need communities detection, which is a complex and expensive task. We validate our algorithm using different publicly available data-sources. In real large scale scenarios, our algorithm achieves approximately the same delivery ratio of the state-of-art solution with up to 40 less network overhead.
  @cite_22: 
  @cite_1: While the demand for wearable sensor devices is going to rise significantly in the near future, Long Term Evolution (LTE) chips are becoming progressively less expensive and rich in functionalities, suggesting for a strong integration between these two technologies. Moreover, the introduction of the Device-to-Device (D2D) feature in LTE envisages direct communication for basically any kind of device, and wearable sensors can be one of those. In this way, collaborative applications based on wearable sensors would benefit from the extended range and higher throughput offered by LTE. However, when sensor devices achieve cellular coverage, security of direct links and of wearable applications become crucial. In particular, especially in critical and emergency scenarios, direct connectivity has to be guaranteed to all the nodes. Starting from this requirement and using a secure LTE D2D protocol, in this paper we provide the analytical and simulation results in terms of achievable connectivity for a possible deployment of a LTE-enabled collaborative wearable network for emergency or extreme sport applications.
  @cite_32: The Internet-of-Things (IoT) is promising to inter-connect physical objects and machines in an intelligent network. In this context, scalable and resilient Machine-to-Machine (M2M) communication protocols are required, and the new Device-to-Device (D2D) feature of the 4G system constitutes an appealing solution. Standardization activities are still in progress, but the rapid diffusion of both LTE and IoT devices and applications leads to development of experimental proposals aimed at merging these two technologies. We contribute in this work with a novel D2D communication protocol, which enables user equipments (UEs) to become the hubs of machine-type traffic by means of a suitable radio interface and upload data in the Web via the mobile network, thus opening to new cloud services. The protocol we propose is designed for multi-hop communications between D2D-enabled terminals and it is equipped with a light-weight security mechanism. It is meant to address the communication needs of UEs inside mobile network coverage, and those of UEs that suffer from scarce radio coverage. In terms of performance, we analyse connectivity and security in the multi-hop D2D network, taking into account the interference created by the transmission of beacon signals during the discovery phase of the wide network. We resort to stochastic geometry to model the end-to-end delay and communication resilience of the multi-hop D2D network.
  @cite_15: In this paper, we represent performance comparison of V2V communications. We apply LTE-D2D with MIMO or cooperative schemes to get low latency and reliability. In cooperative communication, respective links between transmitters and receivers are affected by different values of CFO. Therefore, cooperative communication has different CFO values in contrast with MIMO system. Simulation results show that BLER performances are decreased according to increased CFO and relative velocity. Especially, performances of the MIMO system which are affected by high CFO are further poor. Thus, cooperative communication can be more suitable for V2V communication because of diverse values of CFO.
  @cite_10: Device-to-Device (D2D) communication is an important feature for many kinds of mobile networks and in particular for the UMTS Long Term Evolution Advanced (LTE-A) cellular technology, where an underlay network can be created between User Equipments (UEs) without the support of an evolved Node B (eNB). The possibility to allow direct links between UEs plays an important role when the commercial LTE infrastructure is subject to failures or becomes unavailable after a disaster. Project ABSOLUTE, in scenarios for public safety, proposes raising in the sky a balloon with attached a 4G eNB (AeNB) to restore temporarily connectivity. In all cases in which UEs are out-of-coverage of the AeNB like in indoors, D2D becomes crucial. In this work, we propose to establish direct links employing a communication protocol that relies on the transmission of beacon frames sent in broadcast mode by selected UEs. We delve security aspects of this D2D protocol suitable for Public Safety (PS) users with out-of-coverage UEs based on sharing encryption keys. We pursue a network connectivity analysis of the secure protocol whereby we are able to show the existence of tradeoff points between connectivity and the increased overhead added by security for different values of the system parameters.
summary: In this work we explore group meetings to enable opportunistic routing in multihop D2D networks. Previous efforts explore D2D in several ways to provide different applications. @cite_10 propose a D2D protocol for public safety use cases, such as natural disasters with massive people concentration. The protocol includes device discovery through beacon broadcast using encryption keys to set up secure D2D communication links. Some works have shown the potential of using LTE-D2D to provide communication in infrastruture-less settings, such as in wearable networks @cite_1 and in the internet of things @cite_32 . Vehicular networks may also benefit from the adoption of D2D. @cite_22 , the authors propose a traffic flow model based on a dynamic resource allocation algorithm to deal with the problem of vehicular communication, sharing the same licensed frequency spectrum as D2D communications, in a single LTE cell. @cite_15 , the combination of LTE-D2D with MIMO is proposed to achieve low latency and better reliability in vehicular communication.