Robert Schober

Smart Grid Communications and Networking: Demand-side management for smart grid: opportunities and challenges

Introduction Demand-side management (DSM) is one of the key components of the future smart grid to enable more efficient and reliable grid operation [1]. To achieve a high level of reliability and robustness in power systems, the grid is usually designed for peak demand rather than for average demand. This usually results in an under-utilized system. To remedy this problem, different programs have been proposed to shape the daily energy consumption pattern of the users in order to reduce the peak-to-average ratio in load demand and use the available generating capacity more efficiently, avoiding the installation of new generation and transmission infrastructures. However, the increasing expectations of the customers both in quantity and quality [2], emerging new types of demand such as plug-in hybrid electric vehicles (PHEVs), which can potentially double the average household energy consumption [3], the limited energy resources, and the lengthy and expensive process of exploiting new resources give rise to the need for developing some more advanced methods for DSM. Since electricity cannot be stored economically, wholesale prices (i.e., prices set by competing generators to regional electricity retailers) vary drastically between the low-demand times of day and the high-demand periods. However, these changes are usually hidden from retail users. That is, end users are usually charged with some average price. To alleviate this problem, various time-differentiated pricing methods have been proposed in the literature. Some examples include day-ahead pricing, time-of-use pricing, critical-peak-load pricing, and adaptive pricing [4–7]. By equipping users with two-way communication capabilities in smart grid systems and by adopting real-time pricing (RTP) methods, it is possible to reflect the fluctuations of wholesale prices to retail prices.

Non-Orthogonal Multiple Access (NOMA) for 5G Systems

Radio access technologies for cellular communications are characterized by multipleaccess schemes whose purpose is to serve multiple users with limited bandwidth resources. Typical examples of multiple access schemes are frequency division multiple access (FDMA), time division multiple access (TDMA), code division multiple access (CDMA), and orthogonal frequency division multiple access (OFDMA). In the history of mobile communications, multiple access schemes have been widely investigated in various types of cellular networks, from the first generation (1G) to the fourth generation (4G). Specifically, the FDMA scheme was used in the 1G system, the TDMA scheme was employed in the second generation (2G) systems, CDMA was the dominant multiple access scheme in the third generation (3G) systems, and the OFDMA scheme has been widely used in 4G systems. In many conventional multiple access schemes, such as TDMA and OFDMA, different users are allocated to orthogonal resources in either the time or the frequency domain in order to alleviate interuser interference. However, the spectral efficiency of these orthogonal multiple access (OMA) schemes is low, since bandwidth resources occupied by users with poor channel conditions cannot be shared by others. As a result, these OMA schemes are not sufficient to handle the explosive growth in data traffic in the mobile Internet of the fifth generation (5G) networks. On the other hand, the chip rates of a CDMA system need to be much higher than the information data rates, which means that the use of CDMA in 5G is also potentially problematic owing to the ultra-high data rates expected in 5G systems. Consequently, in 5G networks, new, sophisticated multiple access technologies are needed to support massive connectivity for a very large number of mobile users and/or Internet of Things (IoT) devices with diverse quality-of-service (QoS) requirements [1]. Multiple access in 5G mobile networks is an emerging and challenging research topic, since it needs to provide massive connectivity, large system throughput and small latency simultaneously [2, 3]. Among the promising candidates for 5G multiple access, NOMA has received considerable attention in particular [4–7]. In contrast to conventional OMA, NOMA can accommodate user fairness via non-orthogonal resource allocation and, therefore, is also expected to increase the system throughput.

Cost-Aware Cellular Networks Powered by Smart Grids and Energy Harvesting

Introduction To meet the dramatic growth in wireless data traffic driven by the popularity of new mobile devices and mobile applications, the fifth generation (5G) of cellular technology has recently attracted a lot of research interest from both academia and industry (see, e.g., [1]). As compared with its fourth generation (4G) counterpart, 5G is expected to achieve a roughly 1000 times data rate increase via dense base station (BS) deployments and advanced physical layer communication techniques [1]. However, the large number of BSs will lead to large energy consumption and high electricity bills for cellular operators, which amounts to a large portion of their operational expenditure. For example, China Mobile owned around 920000 BSs in 2011 and the total energy cost per year was almost 3 billion US dollars, given that the annual cost for each BS is about 3000 US dollars [2]. Therefore, in the 5G era, it is becoming necessary for these cellular operators to reduce their energy costs by employing new cost-saving solutions in the design of cellular BSs, which are our main focus in this chapter. In general, these cost-saving solutions can be categorized into two classes, which manage the energy supply and the communication demand of cellular BSs, respectively [2–5]. On the supply side, one commonly adopted solution is to use energy harvesting devices (e.g., solar panels and wind turbines) at cellular BSs, which can harvest cheap and clean renewable energy to reduce or even substitute for the energy purchased from the grid [5]. However, since renewable energy is often randomly distributed in both time and space and cellular BSs are very energy-hungry, it is very difficult to solely use different BSs’ individually harvested energy to power their operation. As a result, the power grid is still needed to provide reliable energy to BSs. Besides serving as a reliable energy supply, the power grid also provides new opportunities for saving the BSs’ costs with its ongoing paradigm shift from the traditional grid to the smart grid. Unlike the traditional grid, which uses a one-way energy flow to deliver power from central generators to electricity users, the smart grid deploys smart meters at end users to enable both two-way information and two-way energy flows between the grid and the end users [6, 7].

Full-Duplex Protocol Design for 5G Networks

Introduction This chapter concerns the usage of in-band full-duplex transceivers in the emerging fifth generation (5G) wireless systems. The specific focus of the treatment of the topic is on the design and analysis of wideband physical layer and link layer data transmission protocols for heterogeneous networks, i.e., how to take advantage of the capability for simultaneous transmission and reception on the same frequency band provided by recent developments in self-interference cancellation. First of all, we modernize the basic definition of the term ‘full-duplex’ such that it is applicable to 5G systems and consistent with the research communitys new conception of the terminology. The technical challenges of the full-duplex technology are the self-interference and co-channel interference that are the price of its main advantage: improved spectral efficiency by frequency reuse. Here, we characterize the fundamental rate–interference trade-off imposed by the choice between full- and half-duplex modes in a primitive three-terminal system. Thereafter, our discussion proceeds to the design and analysis of full-duplex transmission protocols for 5G communication links. The benefits of spectrum reuse by employing the full-duplex mode in this case are reduced by any kind of asymmetry in the system. In particular, the requested input and output data rates to and from a transceiver are not necessarily equal, and there may be imbalances between corresponding channels or even within them in wideband transmission. The remainder of this chapter is organized as follows. Section 9.2 serves as an introduction to the basics of in-band full-duplex operation, namely its definition, purpose, challenges, and advantages at large. Section 9.3 discusses the design of full-duplex transmission protocols for heterogeneous 5G networks, identifying the types of communication links for which the technology could be suitable. Section 9.4 analyzes the performance of full-duplex transmission over wideband fading channels in typical asymmetric communication scenarios. Finally, Section 9.5 concludes the discussion with some visions of prospective future research directions and the schedule for adopting full-duplex technology for commercial use. Basics of Full-Duplex Systems In-Band Full-Duplex Operation Mode Over the last few years, the research community working on state-of-the-art wireless concepts has been realigning its conception of some very basic terminology related to bidirectional communication and the operation modes of transceivers. In particular, the notion of duplex(ing) has undergone a complete transformation.

Flexible Physical Layer Design

Introduction The role of software in mobile communication systems has increased over time. For the upcoming fifth generation (5G) mobile networks, the concept of software-defined networking (SDN) can ease network management by enabling anything as a service. Software-defined radio (SDR) enables radio virtualization, where several radio components are implemented in software. Cognitive radio (CR) goes one step further by using a software-based decision cycle to self-adapt the SDR parameters and consequently optimize the use of communication resources. This proposal leads to the possibility of having real-time communication functionalities at virtual machines in cloud computing data centers, instead of deploying specialized hardware. Network functions virtualization (NFV) claims to provide cloud-based virtualization of network functionalities. The perspective is that all these software-based concepts should converge while 5G networks are being designed. A new breakthrough will be achieved when all these software paradigms are applied to the physical layer (PHY), where its functionalities are defined and controlled by software as well. A flexible PHY design is particularly beneficial considering the diverse applications proposed for 5G [1]. In fact, these applications typically have conflicting design objectives and face extreme requirements. Broadband communication will play an important role in, for instance, offering video streaming services with high resolution for TV and supporting high-density multimedia such as 4K and 3D videos in smartphones. Data rates up to 10 gigabits per second (Gbps) are therefore being targeted in 5G. The Tactile Internet [2] enables one to control virtual or real objects via wireless links with haptic feedback. This implies that the end-to-end latency constraint in 5G must be dropped by at least one order of magnitude compared with current fourth generation (4G) technologies. The Internet of Things (IoT) is aimed at connecting a massive amount of devices. Wireless sensor networks need to provide in-service monitoring at low cost and with a long battery life. Smart vehicles improve safety and actively avoid accidents by exchanging their driving status, such as position, breaking, acceleration, and speed, with surrounding vehicles and infrastructure via challenging doubly dispersive channels. Overall, this demands asynchronous multiple access, ultra-low latency, and ultra-high reliability.

Cloud Radio Access Networks for 5G Systems

According to a report from Cisco [1], global mobile data traffic will continue to grow rapidly from 2015 to 2020. Meanwhile, the fifth generation (5G) is required to enhance the telecommunications infrastructure and provide new information services to support vertical applications in a variety of industrial areas, such as agriculture, medicine, finance, transportation, manufacturing, and education. Therefore, 5G requires innovative solutions to meet new demands from both the mobile Internet and the Internet of Things (IoT) in terms of user-experienced data rate improvement, latency reduction, connection density and area capacity density enhancement, mobility enhancement, and spectral efficiency and energy efficiency improvements. According to the International Telecommunication Union (ITU), the current 5G scenarios can be divided into three categories: enhanced mobile broadband (eMBB), massive machine-type communications (mMTC), and ultra-reliable low-latency communications (URLLC). Hotspots (indoor/outdoor), wide-area coverage, and high speed are typical use cases. Performance measures of human-centric communications such as the ultimate user experience are primary targets in the eMBB scenario. Use cases of mMTC include the monitoring and automation of buildings and infrastructure, smart agriculture, logistics, tracking, and fleet management. A high connection density, low complexity and cost, and long battery life are essential objectives in the mMTC scenario. There are many representative use cases related to URLLC, such as remote machinery and intelligent transportation systems. Low latency and high reliability are key points that need to be taken into account in the design of the radio technology in order to solve the problem of the specific requirements of URLLC scenarios. Rethinking the Fundamentals for 5G Systems The 5G network is anticipated to be soft, green, and superfast [2]. To meet the critical requirements for various scenarios, it is simply not enough for 5G to evolve from current fourth generation (4G) systems. Rather, it requires a revolutionary path. In [2–4], it was proposed to rethink the fundamentals from seven perspectives, such as architectures, protocols, and functions, to revolutionarily redesign future 5G networks, including: 1. Rethinking Shannon, which is to take a green metric such as the energy efficiency as a key performance indicator of wireless systems. 2. Rethinking Ring and Young, which is to break the boundary of conventional cells. As we move toward the timeline of 2020 with the introduction of heterogeneous networks (HetNets) and ultra-dense networks (UDNs), multiple layers of radio networks have come into being.

Electric vehicle charging stations with renewable power generators: A game theoretical analysis

In this paper, we study the price competition among electric vehicle charging stations (EVCSs) with renewable power generators (RPGs). As electric vehicles (EVs) become more popular, a competition among EVCSs to attract EVs is inevitable. Thereby, each EVCS sets its electricity price to maximize its revenue by taking into account the competition with neighboring EVCSs. We analyze the competitive interactions between EVCSs using game theory, where relevant physical constraints such as the transmission line capacity, the distance between EV and EVCS, and the number of charging outlets at the EVCSs are taken into account. We show that the game played by EVCSs is a supermodular game and there exists a unique pure Nash equilibrium for best response algorithms with arbitrary initial policy. The electricity price and the revenue of EVCSs are evaluated via simulations, which reveal the benefits of having RPGs at the EVCSs.