(1987). Applied Probability and Queues. Journal of the Operational Research Society: Vol. 38, No. 11, pp. 1095-1096.

https://link.springer.com/content/pdf/10.1057%2Fjors.1987.184.pdf

Applied Probability and Queues

Recent emphasis on green communications has generated great interest in the investigations of energy harvesting communications and networking. Energy harvesting from ambient energy sources can potentially reduce the dependence on the supply of grid or battery energy, providing many attractive benefits to the environment and deployment. However, unlike the conventional stable energy, the intermittent and random nature of the renewable energy makes it challenging in the realization of energy harvesting transmission schemes. Extensive research studies have been carried out in recent years to address this inherent challenge from several aspects: energy sources and models, energy harvesting and usage protocols, energy scheduling and optimization, implementation of energy harvesting in cooperative, cognitive radio, multiuser and cellular networks, etc. However, there has not been a comprehensive survey to lay out the complete picture of recent advances and future directions. To fill such a gap, in this paper, we present an overview of the past and recent developments in these areas and highlight a number of possible future research avenues.

/pdf/advances-in-energy-harvesting-communications-past-present-3oubbkeycy.pdf

Advances in Energy Harvesting Communications: Past, Present, and Future Challenges

Energy harvesting (EH) from ambient radio-frequency (RF) electromagnetic waves is an efficient solution for fully autonomous and sustainable communication networks. Most of the related works presented in the literature are based on specific (and small-scale) network structures, which although give useful insights on the potential benefits of the RF-EH technology, cannot characterize the performance of general networks. In this paper, we adopt a large-scale approach of the RF-EH technology and we characterize the performance of a network with random number of transmitter-receiver pairs by using stochastic-geometry tools. Specifically, we analyze the outage probability performance and the average harvested energy, when receivers employ power splitting (PS) technique for "simultaneous" information and energy transfer. A non-cooperative scheme, where information/energy are conveyed only via direct links, is firstly considered and the outage performance of the system as well as the average harvested energy are derived in closed form in function of the power splitting. For this protocol, an interesting optimization problem which minimizes the transmitted power under outage probability and harvesting constraints, is formulated and solved in closed form. In addition, we study a cooperative protocol where sources' transmissions are supported by a random number of potential relays that are randomly distributed into the network. In this case, information/energy can be received at each destination via two independent and orthogonal paths (in case of relaying). We characterize both performance metrics, when a selection combining scheme is applied at the receivers and a single relay is randomly selected for cooperative diversity.

/pdf/simultaneous-information-and-energy-transfer-in-large-scale-11857a8bvk.pdf

Simultaneous Information and Energy Transfer in Large-Scale Networks with/without Relaying

We consider a cognitive radio network with an energy-harvesting secondary transmitter to improve both energy efficiency and spectral efficiency. The goal of this paper is to determine an optimal spectrum sensing policy that maximizes the expected total throughput subject to an energy causality constraint and a collision constraint. The energy causality constraint comes from the fact that the total consumed energy should be equal to or less than the total harvested energy, while the collision constraint is required to protect the primary user. We first show that the system can be divided into a spectrum-limited regime and an energy-limited regime depending on where the detection threshold for the spectrum sensor lies. Assuming infinite battery capacity, we derive the optimal detection threshold that maximizes the expected total throughput subject to the energy causality constraint and the collision constraint. Analytical and numerical results show that the system is energy-limited if the energy arrival rate is lower than the expected energy consumption for a single spectrum access. They also show that a decreasing probability of accessing the occupied spectrum does not always result in decreased probability of accessing the idle spectrum in the energy-limited regime.

Cognitive Radio Networks with Energy Harvesting

Device-to-Device Communication in Cellular Networks

Exploiting the unlicensed spectrum is considered by 3GPP as one promising solution to meet ever-increasing traffic growth. As a result, one major enhancement for LTE in Release 13 has been to enable its operation in the unlicensed spectrum via licensed-assisted access (LAA). In this article, we provide an overview of the Release 13 LAA technology including motivation, use cases, LTE enhancements for enabling the unlicensed band operation, and the coexistence evaluation results contributed by 3GPP participants.

Licensed-Assisted Access to Unlicensed Spectrum in LTE Release 13

The Long Term Evolution (LTE) in unlicensed spectrum is an emerging topic in the 3rd Generation Partnership Project (3GPP), which is about an operation of the LTE system in the unlicensed spectrum via license-assisted carrier aggregation. The 5 GHz Unlicensed National Information Infrastructure (U-NII) bands are currently under consideration, but these bands are also occupied by Wireless Local Area Networks (WLAN), specifically those based on the IEEE 802.11a/n/ac technologies. Therefore, an appropriate coexistence mechanism must be augmented to guarantee a peaceful coexistence with the incumbent systems. With this regard, our focus lies on the evaluation of all the proposed coexistence mechanisms so far in a single framework and making a fair comparison of them. The coexistence mechanisms covered in this work includes static muting, listen-before-talk (LBT), and other sensing-based schemes that make a use of the existing WLAN channel reservation protocol.

LTE in the unlicensed spectrum: Evaluating coexistence mechanisms

This paper considers the scenario in which a set of nodes share a common channel. Some nodes have a rechargeable battery and the others are plugged to a reliable power supply and, thus, have no energy limitations. We consider two source-destination pairs and apply the concept of cognitive radio communication in sharing the common channel. Specifically, we give high-priority to the energy-constrained source-destination pair, i.e., primary pair, and low-priority to the pair which is free from such constraint, i.e., secondary pair. In contrast to the traditional notion of cognitive radio, in which the secondary transmitter is required to relinquish the channel as soon as the primary is detected, the secondary transmitter not only utilizes the idle slots of primary pair but also transmits along with the primary transmitter with probability p. This is possible because we consider the general multipacket reception model. Given the requirement on the primary pair's throughput, the probability p is chosen to maximize the secondary pair's throughput. To this end, we obtain two-dimensional maximum stable throughput region which describes the theoretical limit on rates that we can push into the network while maintaining the queues in the network to be stable. The result is obtained for both cases in which the capacity of the battery at the primary node is infinite and also finite.

Optimal utilization of a cognitive shared channel with a rechargeable primary source node

The 3GPP is in the process of developing the next generation radio access technology, named New Radio (NR), which will be proposed as a candidate technology for IMT-2020. This article outlines the wide bandwidth operation of NR, among other new features being considered, based on the up-to-date discussions and decisions made in 3GPP standardization meetings. The much wider channel bandwidth of NR, compared to LTE, enables more efficient use of resources than the existing carrier aggregation framework with lower control overhead. The support of multiple sub-carrier spacing options allows NR to operate in a wide range of carrier frequency from sub-6 GHz band to mmWave band with appropriate handling of multi-path delay spread and phase noise depending on the carrier frequency. In addition, the introduction of the new bandwidth part concept allows flexible and dynamic configuration of UE's operating bandwidth, which will make NR an energy-efficient solution despite the support of wide bandwidth. Other NR wideband operation related issues, such as the support of UEs with limited RF capability and frequency domain resource indexing, are also explained in this article.

NR Wide Bandwidth Operations

In this paper, we consider the random access of nodes having energy harvesting capability and a battery to store the harvested energy. Each node attempts to transmit the head-of-line packet in the queue if its battery is nonempty. The packet and energy arrivals into the queue and the battery are all modeled as a discrete-time stochastic process. The main contribution of this paper is the exact characterization of the stability region of the packet queues given energy harvesting rates for the two-node slotted ALOHA system. By stability, we refer the ability of a system to keep the queues in a bounded region, or more precisely, the existence of the limiting distribution for the joint queue length process. The analysis is non-trivial even for the two-node case because it involves the interaction between nodes of having both the packet queue and the battery. The result is obtained for both scenarios in which the capacity of batteries is infinite and also finite.

Jeon Jeongho

Papers

Licensed-Assisted Access to Unlicensed Spectrum in LTE Release 13

LTE in the unlicensed spectrum: Evaluating coexistence mechanisms

Optimal utilization of a cognitive shared channel with a rechargeable primary source node

NR Wide Bandwidth Operations

The stability region of random multiple access under stochastic energy harvesting