The low power wide area network (LPWAN) technologies, which is now embracing a booming era with the development in the Internet of things (IoT), may offer a brand new solution for current smart grid communications due to their excellent features of low power, long range, and high capacity. The mission-critical smart grid communications require secure and reliable connections between the utilities and the devices with high quality of service (QoS). This is difficult to achieve for unlicensed LPWAN technologies due to the crowded license-free band. Narrowband IoT (NB-IoT), as a licensed LPWAN technology, is developed based on the existing LTE specifications and facilities. Thus, it is able to provide cellular-level QoS, and henceforth can be viewed as a promising candidate for smart grid communications. In this paper, we introduce NB-IoT to the smart grid and compare it with the existing representative communication technologies in the context of smart grid communications in terms of data rate, latency, and range, etc. The overall requirements of communications in the smart grid from both quantitative and qualitative perspectives are comprehensively investigated and each of them is carefully examined for NB-IoT. We further explore the representative applications in the smart grid and analyze the corresponding feasibility of NB-IoT. Moreover, the performance of NB-IoT in typical scenarios of the smart grid communication environments, such as urban and rural areas, is carefully evaluated via Monte Carlo simulations.

In this paper, we investigate the relay selection (RS) problem in full-duplex (FD) two-way relay networks, where the relays are wirelessly powered by harvesting a portion of the received signal power from the sources. To the best of the authors' knowledge, this is the first investigation of FD two-way relays with simultaneous wireless and information transfer capabilities. For each relay, we prove the quasi convexity of the power splitting (PS) factor optimization, and obtain the optimal PS factor in terms of the outage probability by linear search. Both single relay selection (SRS) and general relay selection (GRS) without the limit on the number of cooperating relays are investigated and the corresponding RS methods are proposed. Since the optimal GRS problem is computationally intractable with exponential complexity, we propose several low-complexity heuristic GRS methods based on various relay ordering and greedy selection criteria. Simulations indicate that the proposed GRS methods perform better than the SRS methods and achieve very similar performance compared with the optimal RS method achieved by exhaustive search but with dramatically reduced complexity.

Recent developments and advances in distributed energy resource (DER) technologies make them valuable assets in microgrids. This paper presents an innovative evaluation framework for microgrid assets to capture economic benefits from various grid and behind-the-meter services in grid-connecting mode and resilience benefits in islanding mode. In particular, a linear programming formulation is used to model different services and DER operational constraints to determine the optimal DER dispatch to maximize economic benefits. For the resiliency analysis, a stochastic evaluation procedure is proposed to explicitly quantify the microgrid survivability against a random outage, considering uncertainties associated with photovoltaic (PV) generation, system load, and distributed generator failures. Optimal coordination strategies are developed to minimize unserved energy and improve system survivability, considering different levels of system connectedness. The proposed framework has been applied to evaluate a proposed microgrid in Northampton, Massachusetts that would link the Northampton Department of Public Works, Cooley Dickenson Hospital, and Smith Vocational Area High School. The findings of this analysis indicate that over a 20-year economic life, a 441 kW/441 kWh battery energy storage system, and 386 kW PV solar array can generate $2.5 million in present value benefits, yielding a 1.16 return on investment ratio. Results of this study also show that forming a microgrid generally improves system survivability, but the resilience performance of individual facilities varies depending on power-sharing strategies.

In recent years, the capacity and charging speed of batteries have become the bottleneck of mobile communications systems. With the development of wireless power transfer technologies, simultaneous wireless information and power transfer (SWIPT) emerges as a potential solution for green communications. Due to hardware limitations, the energy harvesting circuit cannot decode the signal directly. Power splitting is a popular and effective solution to this problem. Consequently, the problem of optimal power splitting at the receiver arises in addition to the conventional problem of power allocation in communications systems. SWIPT in vehicular networks is a promising technology that helps extend the lifetime of sensors installed on vehicles and roadside units. However, existing SWIPT schemes fail to consider the doubly selective characteristics of vehicular channels. In this paper, joint power allocation and splitting for SWIPT over such channels is proposed with the objective of maximizing the achievable data rate with constraints on the delivered energy. Simulations show significantly improved performance compared with the existing dynamic power splitting scheme. A suboptimal algorithm, named decoupled power allocation and splitting, is also proposed with significantly reduced computational complexity and simulations demonstrate its near-optimum performance.

In this study, we investigate the relay selection (RS) problem in full-duplex energy-harvesting (FDEH) relay networks, where the relays are wirelessly powered by harvesting a portion of the received signal power from the source. We extend the investigation of the relay selection problem in FDEH relay networks to enable multiple relays to be selected simultaneously for improved performance. This is in contrast with existing studies on RS in similar setups, where only one relay can be selected in a transmission cycle. Our simulations show that selecting only a single relay is not always optimal, especially at low signal-to-noise ratios (SNRs). Furthermore, in this paper, we present the design of a greedy RS method with quadratic complexity for FDEH relay networks. Compared with the exhaustive-search-based RS, the proposed greedy RS achieves near-optimum performance in terms of the end-to-end capacity with significantly reduced complexity.