Abstract-Energy-efficient communication techniques play great roles in applications where devices are powered by batteries. Relaying is viewed as an energy saving technique because it can reduce the transmit power by breaking one long range transmission into several short range transmissions. Two-Way Relaying Transmission (TWRT) is expected to consume less transmit power than One-Way Relaying Transmission (OWRT). In this paper, we study the Energy Efficiencies (EEs) of One-Way Decode-and-Forward (OWDF) and Two-Way Decode-and-Forward (TWDF) systems with delay constraint. The maximum EEs of both systems are derived by jointly optimizing the transmission duration and the transmit power allocation. Analytical and simulation results show the impacts of packet size, time deadline and the channel gain to EE.

Energy Efficiency (EE) of cellular networks has received considerable attention recently. However, EE of relayassisted cellular networks has not been thoroughly addressed, especially that the MBSs adopt multi-antenna. In this paper, considering downlink transmission of multi-antenna relayassisted cellular network where the MBSs and RSs are deployed in the Euclidean plane according to independent homogeneous Poisson point processes, meanwhile, an sleep mode strategy is used in MBS, a geometric model is built to derive the coverage probability for the MBS to user (UE), the MBS to Relay Station (RS), the RS to UE links and analyze the system EE. A metric defined as the ratio of average network throughput to average network power consumption is used to measure the average EE and its analytical expression is derived. Simulation results confirm the theoretical findings and demonstrate that the MBSs equipped with multi-antenna has better performance on energy efficiency and coverage probability of every link than that with single antenna.

Two-way amplify-and-forward (AF) relaying networks have been widely studied because of its simplicity and high spectral efficiency. In this paper, we investigate the relay selection problem and the diversity-multiplexing tradeoff (DMT) for two-way AF relaying systems over independent flat Rayleigh fading channels. We first derive the closed-form expression of the minimum total transmit power under the predefined data rate requirements. Based on the minimum total transmit power, we propose a simple relay selection which only requires user-relay channel state information (CSI). We proved that the proposed relay selection scheme can achieve the same DMT performance as obtained by the popular outage-optimal two-way opportunistic relaying scheme. Simulation results demonstrate that the proposed scheme can significantly decrease the power consumption compared with random relay selection and other schemes.

The Poisson point process (PPP) is widely used in wireless network modeling and performance analysis because it can provide tractable results for heterogeneous cellular networks (HetNets) analysis. However, it cannot accurately reflect the spatial distribution characteristics of the actual base stations (BSs). Considering the fact that the distribution of macro base stations (MBSs) is exclusive, the deployment of MBSs is modeled by the Matérn hard-core point process (MHCPP), and the deployment of pico base stations (PBSs) is modeled by PPP. This paper studies the performance of multiantenna HetNets and improves the energy efficiency (EE) of HetNets by optimizing the transmit power of PBSs. We use a simple approximate method to study the signal-to-interference ratio (SIR) distribution in two-tier MHCPP-PPP HetNets and derive the coverage probability, average data rate and EE of HetNets. Then, an optimization algorithm is proposed to improve the EE of HetNets. Finally, three transmission technologies are simulated and analyzed. The results show that multiantenna transmission has better system performance than single antenna transmission and that selecting the appropriate transmit power for a PBS can effectively improve the EE of the system. In addition, two-tier MHCPP-PPP HetNets have higher EE than two-tier PPP-PPP HetNets.