Energy efficiency improvement in cloud radio access networks (CRANs) using device centric caching policies

Abstract

As the demand for wireless services is projected to double every year, wireless system designers are facing a major crisis to cater to this demand with the conventional cellular network architecture due to the scarcity of spectrum resources and high cost of energy consumption. Therefore, major architectural changes such as cloud radio access networks (CRANs) and device-to-device (D2D) communications have been proposed as potential solutions. The proposed research project is mainly focuses on improving the performance of the CRAN architecture. Firstly, we propose a spectrum selection scheme and a transmit power minimization scheme for a D2D network cross-laid with a CRAN. The D2D communications are allowed as an overlay to the CRAN as well as in the unlicensed industrial, scientific and medical radio (ISM) band. A link distance-based scheme is proposed and closed-form approximations are derived for the link distance thresholds to select the operating band of the D2D users. Furthermore, analytical expressions are derived to calculate the minimum required transmit power to achieve a guaranteed level of quality of service in each operating band. Secondly, a novel content caching strategy is proposed for a cache enabled D2D network where the user devices are allowed to communicate using millimeter wave (mmWave) D2D links (> 6 GHz) as well as conventional sub 6 GHz cellular links. The proposed content placement strategy maximizes the successful content delivery probability of a line-of-sight D2D link. Furthermore, a heuristic algorithm is proposed for efficient content delivery. The overall scheme improves the successful traffic offloading gain of the network compared to conventional cache-hit maximizing content placement and delivery strategies. Significant energy efficiency improvements can also be achieved in ultra-dense networks. Finally, we consider the physical layer security of an untrusted unmanned aerial vehicle (UAV) based D2D network, operating in full-duplex mode. A source-based jamming scheme is exploited for secure communication without utilizing any external jammers. Firstly, the optimal power allocation between the confidential signal and the jamming signal is derived to maximize the secrecy rate of each link between the source and the destination. Then, the best UAV selection scheme is proposed to maximize the overall secrecy rate of the network. The corresponding secrecy outage probability and the average secrecy rate of the network are analyzed based on the proposed UAV selection and the optimal power allocation schemes. Asymptotic results are also obtained to derive the achievable diversity order.