No abstract

Spectral efficiency (SE) and energy efficiency (EE) are the main metrics for designing wireless networks. Rather than focusing on either SE or EE separately, recent works have focused on the relationship between EE and SE and provided good insights into the joint EE-SE tradeoff. However, such works have assumed that bandwidth are fully occupied regardless of the transmission requirements and therefore are only valid for this scenario. In this paper, we propose a new paradigm for EE-SE tradeoff, namely the resource efficiency (RE) for orthogonal frequency division multiple access (OFDMA) cellular network in which we take into consideration different transmission-bandwidth requirements. We analyse the properties of the proposed RE and prove that it is capable of exploiting the tradeoff between EE and SE by balancing consumption power and occupied bandwidth; hence simultaneously optimizing both EE and SE. We then formulate the generalized RE optimization problem with guaranteed quality of service (QoS) and provide a gradient based optimal power adaptation scheme to solve it. We also provide an upper bound near optimal method to jointly solve the optimization problem. Furthermore, a low-complexity suboptimal algorithm based on uniform power allocation scheme is proposed to reduce the complexity. Numerical results confirm the analytical findings and demonstrate the effectiveness of the proposed resource allocation schemes for efficient resource usage.

Abstract-A new exact explicit expression is derived for the ergodic capacity of maximal ratio combining (MRC) schemes over arbitrarily correlated Rician fading channels. This is used to study the effects of channel correlation on the ergodic capacity. Numerical results reveal that both the phase and the magnitude of correlation have an impact on the ergodic capacity of Rician fading channels. This is in contrast to correlated Rayleigh fading, where the phase of the correlation has no effect on the ergodic capacity. It is also observed that negatively correlated branches in Rician fading may lead to an increase in ergodic capacity beyond that obtained by uncorrelated branches.

Heterogeneous network (HetNet) deployment is considered a de facto solution for meeting the ever increasing mobile traffic demand. However, excessive power usage in such networks is a critical issue, particularly for the mobile operators. Characterizing the fundamental energy efficiency (EE) performance of HetNets is therefore important for the design of green wireless systems. In this paper, we address the EE optimization problem for downlink two-tier HetNets comprised of a single macrocell and multiple pico-cells. Considering a heterogeneous realtime and non-real-time traffic, transmit beamforming design and power allocation policies are jointly considered in order to optimize the system energy efficiency. The EE resource allocation problem under consideration is a mixed combinatorial and nonconvex optimization problem, which is extremely difficult to solve. In order to reduce the computational complexity, we decompose the original problem with multiple inequality constraints into multiple optimization problems with single inequality constraint. For the latter problem, a two-layer resource allocation algorithm is proposed based on the quasiconcavity property of EE. Simulation results confirm the theoretical findings and demonstrate that the proposed resource allocation algorithm can efficiently approach the optimal EE. Index Terms-Green radio (GR), energy efficiency (EE), heterogeneous network (HetNet), resource allocation.

In this paper we analyze the secrecy capacity of a halfduplex energy harvesting (EH)-based multi-antenna amplify-andforward (AF) relay network in the presence of a passive eavesdropper. During the first phase, while the source is in transmission mode, the legitimate destination transmits an auxiliary artificial noise (AN) signal which has here two distinct purposes, a) to transfer power to the relay b) to improve system security. Since the AN is known at the legitimate destination, it is easily canceled at the intended destination which is not the case at the eavesdropper. In this respect, we derive new exact analytical expressions for the ergodic secrecy capacity for various well-known EH relaying protocols, namely, time switching relaying (TSR), power splitting relaying (PSR) and ideal relaying receiver (IRR). Monte Carlo simulations are also provided throughout our investigations to validate the analysis. The impacts of some important system parameters such as EH time, power splitting ratio, relay location, AN power, EH efficiency and the number of relay antennas, on the system performance are investigated. The results reveal that the PSR protocol generally outperforms the TSR approach in terms of the secrecy capacity.Index Terms-Amplify-and-forward relays, cooperative communications, energy harvesting, secrecy capacity, wireless power transfer. Abdelhamid Salem (S'12), received the B.Sc. degree in Electrical and Electronic Engineering from the University of Benghazi, Benghazi, Libya, in 2002 and the M.Sc. degree (with distinction) in Communication Engineering from the University of Benghazi, Benghazi, Libya, in 2009, he is currently working toward the Ph.D. degree in wireless communications with The University of Manchester, United Kingdom . His current research interests include Physical Layer Security, signal processing for interference mitigation, energy harvesting, wireless power transfer, MIMO systems, wireless optical communication systems and power line communications. Khairi Ashour Hamdi (M'99-SM'02) received the B.Sc. degree in electrical engineering from the Alfateh University, Tripoli, Libya, in 1981, the M.Sc. degree (with distinction) from the Technical University of Budapest, Budapest, Hungary, in 1988, and the Ph.D. degree in telecommunication engineering in 1993, awarded by the Hungarian Academy of Sciences. His current research interests include modelling and performance analysis of wireless communication systems and networks.