Constantinos Psomas

Survey on energy harvesting wireless communications: challenges and opportunities for radio resource allocation

Green radio communications has received a lot of attention in recent years due to its impact on telecom business, technology and environment. On the other hand, energy harvesting communication has emerged as a potential candidate to reduce the communication cost by tackling the problem in a contrasting fashion. While green communication techniques focus on minimizing the use of radio resources, energy harvesting communication relies on environment friendly techniques to generate energy from renewable resources and on effective use of the stored energy under the condition that there is always energy available when required. Thus, the focus migrates from minimization of energy to optimal time domain ‘distribution’ of energy, which causes a paradigm shift in radio resource allocation research. This survey summarizes major research work in the area of energy harvesting resource allocation. Instead of just focusing on the power allocation based on average and maximum power constraints, the random energy arrival process and packet/energy buffering interact in a challenging way to open new research problems. First, we present the fundamental concepts in energy harvesting communications and review recent research work in different wireless network applications. We discuss some quantitative results from the existing literature to explain the state of the art work. The energy cooperation aspect of energy harvesting is addressed in detail which has emerged as an interesting area of research recently. Finally, we conclude by summarizing some open challenges for future research and scope for innovation in this emerging area.

Impact of Directionality on Interference Mitigation in Full-Duplex Cellular Networks

In this paper, we consider two fundamental full-duplex (FD) architectures, two-node and three-node, in the context of cellular networks where the terminals employ directional antennas. The simultaneous transmission and reception of data in non-orthogonal channels makes FD radio a potential solution for the currently limited spectrum. However, its implementation generates high levels of interference either in the form of loopback interference (LI) from the output to the input antenna of a transceiver or in the form of co-channel interference in large-scale multicell networks due to the large number of active links. Using a stochastic geometry model, we investigate how directional antennas can control and mitigate the co-channel interference. Furthermore, we provide a model which characterizes the way directional antennas manage the LI in order to passively suppress it. Our results show that both architectures can benefit significantly by the employment of directional antennas. Finally, we consider the case where both architectures are employed in the network and derive the optimal values for the density fraction of each architecture, which maximize the success probability and the network throughput.

Successive Interference Cancellation in Bipolar Ad Hoc Networks With SWIPT

Successive interference cancellation (SIC) is based on the idea that some interfering signals may be strong enough to decode in order to be removed from the aggregate received signal and thus boost performance. In this letter, we study the SIC technique from a simultaneous wireless information and power transfer (SWIPT) standpoint. We consider a bipolar ad hoc network and evaluate the impact of SIC on the SWIPT performance for the power splitting technique. Theoretical and numerical results show that our proposed approach can achieve significant energy gains and under certain scenarios the average harvested energy converges to its upper bound.

Backscatter Communications for Wireless Powered Sensor Networks With Collision Resolution

Wireless powered backscatter communications is an attractive technology for next-generation low-powered sensor networks such as the Internet of Things. However, backscattering suffers from collisions due to multiple simultaneous transmissions and a dyadic backscatter channel, which greatly attenuate the received signal at the reader. This letter deals with backscatter communications in sensor networks from a large-scale point-of-view and considers various collision resolution techniques: directional antennas, ultra-narrow band transmissions, and successive interference cancellation. We derive analytical expressions for the decoding probability and our results show the significant gains, which can be achieved from the aforementioned techniques.

Mobility Management in Ultra-Dense Networks: Handover Skipping Techniques

Ultra-dense network deployment is a key technology for potentially achieving the capacity target of next-generation wireless communication systems. However, such a deployment results in cell proliferation and cell size decrement, leading to an increased number of handovers and limited sojourn time within a cell, which severely degrade the user’s quality of service (QoS). In this paper, we propose two intelligent handover skipping techniques to overcome the high handover rates. The first technique considers a user associated with a single base station (BS) and the decision to skip a handover is based on the upcoming cell’s topology; we consider three criteria: 1) the area of the cell; 2) the trajectory distance within the cell; and 3) the distance of the BS from the cell edge. The second technique exploits BS cooperation and enables a dynamic handover skipping scheme, where the skipping decision is taken based on the BSs of three consecutive cells in the user’s trajectory. This technique achieves a balance between BS cooperation and single BS transmission and manages to maintain a good QoS during the skipping phase. We show that the proposed techniques reduce both the handover rate and handover cost and outperform the conventional techniques for moderate to high-velocity values.

Low-Complexity Base Station Selection Scheme in mmWave Cellular Networks

In this paper, we study the performance of next-generation cellular networks in the context of a low-complexity base station (BS) selection scheme. In contrast to existing BS cooperation approaches, where multiple BSs jointly transmit to the user, by using our proposed low-complexity technique, a user communicates with the BS that provides the maximum signal-to-interference-plus-noise-ratio from a set formed according to a pre-selection policy. We consider three pre-selection policies based on: 1) the Euclidean distance; 2) the averaged received power; and 3) a random selection. Moreover, we consider the case where the users have the ability to employ the successive interference cancellation (SIC) scheme. Despite its high computational complexity, SIC can potentially decode and remove strong interfering signals from the aggregate received signal, which can significantly boost the user’s performance. By using stochastic geometry tools, analytical expressions for the coverage performance are derived for each policy, by taking into account spatial randomness and blockage effects. Our proposed technique provides low computational and implementation complexity due to the two-level selection scheme. Furthermore, we show that our proposed scheme does not lose in diversity compared with existing cooperation techniques and that all policies can benefit by the employment of the SIC scheme.

Low complexity base station cooperation in cellular networks with blockages

Motivated by the effects of buildings/obstacles on the performance of high frequency cellular networks, this paper deals with the base station (BS) cooperation in heterogeneous cellular networks with blockages. Our main focus is a joint transmission scenario, where an ideal backhaul network allows a set of randomly located BSs belonging to different network tiers, to cooperate and jointly transmit data. By using concepts from random shape theory, we model the spatial randomness as well as the main characteristics of the blockages (e.g., size, orientation, etc). The outage probability performance of the system is analyzed for two low complexity transmission techniques with different channel state information requirements by using stochastic geometry tools. Our results show that the spatial diversity associated with the BS cooperation is an efficient technique to overcome the degradation effects of blockages and ensure connectivity.

Low-Complexity Base Station Cooperation for mmWave Heterogeneous Cellular Networks

In this paper, we study the problem of base station (BS) cooperation in millimeter wave multi- tier heterogeneous cellular networks. In contrast to conventional approaches, where a number of BSs jointly transmit data to a user, we investigate a low-complexity technique that enables the selection of a single BS for transmission. Specifically, a single BS that provides the highest instantaneous signal-to-interference-plus- noise ratio is selected, among the strongest BSs from each tier. By using stochastic geometry tools, we derive closed-form expressions for the coverage probability and the diversity gain of the system by taking into account spatial randomness and blockage effects. Our results show that the proposed scheme achieves full diversity and is appropriate for networks with strict computation constraints. In addition, we study the case where users employ successive interference cancellation (SIC) to further boost the achieved performance; SIC allows the mitigation of strong interference terms from the received signal. The impact of SIC on the coverage probability of the system is studied and closed-form expressions are provided.

Blockage effects on joint information & energy transfer in directional ad-hoc networks

The impact of blockages in the performance of next generation wireless networks has recently attracted a lot of attention. In this case, the existence of blockages can provide performance gains as the aggregate interference at a receiver is reduced. Furthermore, the employment of directional antennas at the networks nodes can further boost the performance through the power gains which antenna directionality produces. However, the impact of blockages on wireless power transfer has not been investigated equally. In this paper, we consider a bipolar ad-hoc network where the nodes employ directional antennas and have simultaneous wireless information and power transfer capabilities. We study the effects of blockages and directionality on the energy harvested by a receiver and show that the performance gains from the existence of blockages can be adjusted in order to increase the average harvested energy.

Passive loop interference suppression in large-scale full-duplex cellular networks

Loop interference (LI) in wireless communications, is a notion resulting from the full-duplex (FD) operation. In a large-scale network, FD also increases the multiuser interference due to the large number of active wireless links that exist. Hence, in order to realize the FD potentials, this interference needs to be restricted. This paper presents a stochastic geometry model of FD cellular networks where the users and base stations employ directional antennas. Based on previous experimental results, we model the passive suppression of the LI at each FD terminal as a function of the angle between the two antennas and show the significant gains that can be achieved by this method. Together with the reduction of multiuser interference resulting from antenna directionality, our model demonstrates that FD can potentially be implemented in large-scale directional networks.