Delay-aware cross-layer design for device-to-device communications in future cellular systems

Device-to-device (D2D) communications allow direct communications between nodes without transmitting data via the base stations in cellular systems, which could bring significant performance improvement. Since most applications are delay-sensitive, it is very important to consider delay performance in addition to physical layer throughput for D2D communications. To improve delay performance it is necessary to dynamically control the radio resource in a cross-layer way according to both the channel fading information and the queue length information. The former allows an observation of good transmission opportunity and the latter provides the urgency of data flows. However, the resource control with delay constraints involves stochastic optimization, which is very challenging. In this article we first summarize various approaches to solve the delay-aware resource allocation problems for D2D communications. We propose a low complexity practical solution by exploiting the interference filtering property of CSMA-like MAC protocols in the D2D system. Based on the solution structure, we further discuss the implementation issues based on LTE-Advanced systems and evaluate the associated performance and complexity. Finally we discuss the choice of MAC parameters for the overall D2D system performance. © 1979-2012 IEEE

Enabling Secure Direct Connectivity Under Intermittent Cellular Network Assistance

This work targets at investigating direct communications as a promising technology for the next-generation 5G wireless ecosystem that improves the degrees of spatial reuse and creates new opportunities for users in proximity. While direct connectivity has originally emerged as a technology enabler for public safety services, it is likely to remain in the heart of the 5G ecosystem by spawning a wide diversity of proximate applications and services. Direct communications couples together the centralized and the distributed network architectures, and as such requires respective enablers for secure, private, and trusted data exchange especially when cellular control link is not available at all times. Within the research group, the author was tasked to provide the state-of-the-art technology overview and to propose a novel algorithm for maintaining security functions of proximate devices in case of unreliable cellular connectivity, whenever a new device joins the secure group of users or an existing device leaves it. The proposed solution and its rigorous practical implementation detailed in this work open door to a new generation of secure proximity-based services and applications in future wireless communications systems