Allowing a Device-to-Device (D2D) communication mode in a cellular network is a feature that might improve the system performance due to a better (re)use of radio resources and a reduced congestion when several users located at the same area want to communicate with each other. The design of an efficient D2D communication mode with minimal interference to the cellular network is a key problem for future communication systems. In this work, we study the impact of the distance between communicating and interfering nodes and illustrate the benefits of D2D communication in a cellular network by comparing its performance in terms of total rate with that of a conventional cellular communication mode. The obtained results show that the use of D2D communication might provide considerable gains, but strongly depends on the distances among the involved nodes.

New technologies have emerged to attend the increasing data rates demanded by multimedia services in wireless communication systems. In this context, Device-to-Device (D2D) communication appears as promising feature to improve data rates and increase spectral efficiency of wireless systems. Moreover, its combination with power control, which enables lowpower communication among devices and contributes to reduce interference, can enhance even more such benefits in future wireless systems. In this work, we investigate the leverage of the uplink power control on the D2D communication underlaying cellular networks. The results show that the D2D communication applied together with power control can overcome cellular mode performance in terms of sum rate.

The increasing demand for rich multimedia services and the scarcity of radio resources has motivated the research of technologies able to increase wireless systems' capacity without requiring additional spectrum. In this context, direct Device-to-Device (D2D) communication between User Equipments (UEs) is a promising technology. By allowing direct low-power communication among UEs, D2D communication leads to intelligent spatial reuse of radio resources, permits to offload the network and to increase its capacity and/or Quality of Service (QoS) levels. In this work, we provide a brief literature review on D2D communication, identify and discuss key issues related to the potential benefits of D2D communication within a cellular system, as well as present a distance-based study for defining scenarios in which D2D communication can increase the overall system capacity.

In this work we deal with Congestion Control (CC) strategies to protect the Quality of Service (QoS) of Real Time (RT) services in Orthogonal Frequency Division Multiple Access (OFDMA)-based and packet-switched networks such as Long Term Evolution (LTE) and Worldwide Interoperability forMicrowave Access (WiMAX). Specifically, the first contribution of this paper is the adaptation of a CC strategy previously proposed for High-Speed Downlink Packet Access (HSDPA) to these modern systems. This CC strategy comprises in a coordinated manner the functionalities scheduling, Admission Control (AC) and Load Control (LC). The second contribution is the proposal of a new feature to be added to this CC strategy in order to allow for an early detection of overload situations based on the packet delay of RT flows. In the results we show that our proposed overload prediction based on delay can efficiently prevent QoS degradation of RT flows.

In [1] the authors proposed a Quality of Service (QoS)-driven adaptive Congestion Control (CC) framework that can provide QoS guarantees for the Voice over IP (VoIP) service in mixed traffic scenarios in a single carrier system. The original framework is composed of three Radio Resource Management (RRM) algorithms: Admission Control (AC), Packet Scheduling (PSC) and Load Control (LC). In this work we generalize that framework to systems that employ a multicarrier access scheme such as Orthogonal Frequency Division Multiple Access (OFDMA). In OFDMA-based systems, there is flexibility to exploit the frequency dimension to achieve even better performance gains. In this work, we propose significant changes especially in the PSC functionality where radio resource allocation is performed. Using simulations, we evaluate the generalized CC framework in an OFDMA-based system with a traffic mix composed of sessions from a Real Time (RT) and a Non-Real Time (NRT) service. The results show that the generalized CC framework not only protects the QoS of sessions from the RT service but also imposes only a small performance degradation to the NRT service.