Abstract-In order to minimize electric grid power consumption, energy harvesting from ambient RF sources is considered as a promising technique for wireless charging of low-power devices. To illustrate the design considerations of RF-based ambient energy harvesting networks, this article first points out the primary challenges of implementing and operating such networks, including non-deterministic energy arrival patterns, energy harvesting mode selection, energy-aware cooperation among base stations (BSs), etc. A brief overview of the recent advancements and a summary of their shortcomings are then provided to highlight existing research gaps and possible future research directions. To this end, we investigate the feasibility of implementing RF-based ambient energy harvesting in ultradense small cell networks (SCNs) and examine the related tradeoffs in terms of the energy efficiency and signal-to-interferenceplus-noise ratio (SINR) outage probability of a typical user in the downlink. Numerical results demonstrate the significance of deploying a mixture of on-grid small base stations (SBSs) (powered by electric grid) and off-grid SBSs (powered by energy harvesting) and optimizing their corresponding proportions as a function of the intensity of active SBSs in the network.

In this paper, we consider device-to-device (D2D) communication that is underlaid in a multi-cell massive multipleinput multiple-output (MIMO) system and propose a new framework for power control and pilot allocation. In this scheme, the cellular users (CUs) in each cell get orthogonal pilots which are reused with reuse factor one across cells, while all the D2D pairs share another set of orthogonal pilots. We derive a closed-form capacity lower bound for the CUs with different receive processing schemes. In addition, we derive a capacity lower bound for the D2D receivers and a closed-form approximation of it. We provide power control algorithms to maximize the minimum spectral efficiency (SE) and maximize the product of the signalto-interference-plus-noise ratios in the network. Different from prior works, in our proposed power control schemes, we consider joint pilot and data transmission optimization. Finally, we provide a numerical evaluation where we compare our proposed power control schemes with the maximum transmit power case and the case of conventional multi-cell massive MIMO without D2D communication. Based on the provided results, we conclude that our proposed scheme increases the sum SE of multi-cell massive MIMO networks.

Abstract-This paper studies possibility of using full-duplex (FD) radios in underlay device-to-device communication (D2D) in cellular networks. We consider a cellular system with one D2D pair and one cellular user. Cellular user is sharing the radio resources with D2D link which is equipped with full-duplex radios. The problem of sum-power minimization of cellular system and D2D link both in uplink and downlink period is considered. Considering the interference caused because of exploiting the same radio resources, for uplink period, we use fixed point iterations to solve the optimization problem to calculate transmit powers of users. To design the optimal receiver in the base station, linear minimum mean squared error method is used. In the downlink, to calculate optimal transmit precoder at base station and optimal D2D transmit powers, the optimization problem is formulated as a second order cone problem (SOCP) and solved using CVX in Matlab. Since the available full-duplex radios are not able to cancel the self-interference completely, residual of self-interference is considered in D2D receivers. Performance of the full-duplex D2D with different amounts of self-interference cancelation is compared to that of half-duplex D2D. Results show that full-duplex radios with 110 dB self-interferece cancelation can provide double the throughput for D2D compared to halfduplex radios.

This paper studies the transmit power optimization in a multi-cell massive multiple-input multiple-output (MIMO) system. To overcome the scalability issue of network-wide max-min fairness (NW-MMF), we propose a novel power control (PC) scheme. This scheme maximizes the geometric mean (GM) of the per-cell max-min spectral efficiency (SE). To solve this new optimization problem, we prove that it can be rewritten in a convex form and then solved using standard tools. To provide a fair comparison with the available utility functions in the literature, we solve the network-wide proportional fairness (NW-PF) PC as well. The NW-PF focuses on maximizing the sum SE, thereby ignoring fairness, but gives some extra attention to the weakest users. The simulation results highlight the benefits of our model which is balancing between NW-PF and NW-MMF.

In this paper, we consider a single-cell system where the same radio resources are simultaneously used by a cellular user and a pair of device-to-device (D2D) terminals. The optimization objective is to minimize the sum transmission power of the system while satisfying the user specific minimum rate constraints. We propose joint power control and beamforming algorithms to solve the power minimization problem optimally both in uplink and downlink. In the uplink, the optimal transmit powers for the cellular and D2D users are obtained via fixedpoint iterations, whereas the linear minimum mean squared error receiver is used for optimal reception at the base station (BS). In the downlink, the problem is equivalently reformulated as a second-order cone program (SOCP). As a result, the optimal transmit beamformer for the cellular user and the optimal transmit power for the D2D user can be efficiently computed via standard SOCP solvers. Simulation results demonstrate that the sum power performance can be significantly improved as compared with the conventional cellular system. Results also illustrate that the power consumption of the network is highly affected by the locations of the cellular and D2D users, and whether the resources are shared in the uplink or downlink.