Age Minimization in Energy Harvesting Communications: Energy-Controlled Delays

We consider an energy harvesting source that is collecting measurements from a physical phenomenon and sending updates to a destination within a communication session time. Updates incur transmission delays that are function of the energy used in their transmission. The more transmission energy used per update, the faster it reaches the destination. The goal is to transmit updates in a timely manner, namely, such that the total age of information is minimized by the end of the communication session, subject to energy causality constraints. We consider two variations of this problem. In the first setting, the source controls the number of measurement updates, their transmission times, and the amounts of energy used in their transmission (which govern their delays, or service times, incurred). In the second setting, measurement updates externally arrive over time, and therefore the number of updates becomes fixed, at the expense of adding data causality constraints to the problem. We characterize age-minimal policies in the two settings, and discuss the relationship of the age of information metric to other metrics used in the energy harvesting literature.Comment: Appeared in Asilomar 201

Age-Minimal Transmission in Energy Harvesting Two-hop Networks

We consider an energy harvesting two-hop network where a source is communicating to a destination through a relay. During a given communication session time, the source collects measurement updates from a physical phenomenon and sends them to the relay, which then forwards them to the destination. The objective is to send these updates to the destination as timely as possible; namely, such that the total age of information is minimized by the end of the communication session, subject to energy causality constraints at the source and the relay, and data causality constraints at the relay. Both the source and the relay use fixed, yet possibly different, transmission rates. Hence, each update packet incurs fixed non-zero transmission delays. We first solve the single-hop version of this problem, and then show that the two-hop problem is solved by treating the source and relay nodes as one combined node, with some parameter transformations, and solving a single-hop problem between that combined node and the destination.Comment: Appeared in IEEE Globecom 201

Energy Harvesting Networks with General Utility Functions: Near Optimal Online Policies

We consider online scheduling policies for single-user energy harvesting communication systems, where the goal is to characterize online policies that maximize the long term average utility, for some general concave and monotonically increasing utility function. In our setting, the transmitter relies on energy harvested from nature to send its messages to the receiver, and is equipped with a finite-sized battery to store its energy. Energy packets are independent and identically distributed (i.i.d.) over time slots, and are revealed causally to the transmitter. Only the average arrival rate is known a priori. We first characterize the optimal solution for the case of Bernoulli arrivals. Then, for general i.i.d. arrivals, we first show that fixed fraction policies [Shaviv-Ozgur] are within a constant multiplicative gap from the optimal solution for all energy arrivals and battery sizes. We then derive a set of sufficient conditions on the utility function to guarantee that fixed fraction policies are within a constant additive gap as well from the optimal solution.Comment: To appear in the 2017 IEEE International Symposium on Information Theory. arXiv admin note: text overlap with arXiv:1705.1030

[14C] Radiotracer Studies of the Hydrogenation Reactions Over Supported Platinum Catalysts

The adsorption of acetylene, ethylene and carbon monoxide; the hydrogenation of acetylene and buta-1,3-diene; the effects of sulphur poisoning on the adsorption, and the hydrogenation reactions, have been studied at ambient temperature in a static system using a variety of supported platinum catalysts. The catalysts used were EUROPT-1 (6% Pt/SiO2), EUROPT-3 (0.3% Pt/Al2O3), 0.5% Pt/MoO3, 0.8% Pt/SiO2 and 0.8% Pt/Al2O3. Using the [14-C] radiotracer technique, the shape of acetylene adsorption isotherms over each catalyst showed two distinct adsorption regions, a steep primary region followed (except Pt/MoO3) by a linear secondary region. The Pt/MoO3 catalyst showed a nonlinear secondary region. The adsorption of ethylene also occurred in two distinct stages, but the primary region was less steep than was found with acetylene. The adsorptive capacity of the catalysts for ethylene was approximately one quarter that for acetylene. In contrast, the adsorption isotherms of carbon monoxide showed distinct dissimilarities between catalysts. On EUROPT-1, 0.8% Pt/SiO2 and 0.8% Pt/Al2O3 catalysts, the isotherms displayed different behaviour from that observed with the hydrocarbons in that they showed a prolonged secondary region with a positive gradient. The adsorption isotherm of CO on EUROPT-3 was of a similar shape to the isotherms observed with the hydrocarbons. The Pt/MoO3 catalyst exhibited the expected Langmuir-type CO adsorption isotherm. On steady state catalysts the amount of each adsorbate that can be adsorbed was substantially less than that on freshly reduced catalysts. This has been suggested as being due to the permanently retained hydrocarbon species located at the primary adsorption region. With each catalyst the experimental observations are consistent with the dissociative adsorption of the hydrocarbons on the primary region, whilst the species involved in the actual catalysis process are located on the secondary region and are associatively adsorbed. From the poisoning experiments, evidence has been obtained to show that a surface reconstruction process accompanies the initial adsorption. The results are interpreted in terms of a model involving the migration of metal atoms into the adsorbate ad-layer. The adsorption of acetylene in the presence of gas phase ethylene and vice versa indicates that the adsorption of the two hydrocarbons takes place on the same adsorption sites with acetylene being more strongly adsorbed than ethylene. However, during the hydrogenation of acetylene, hydrogen was found to create sites which were active for the non-competitive adsorption of ethylene. IR evidence has been obtained for the formation of an ethylidyne (-C-CH3) species upon the exposure of a freshly reduced EUROPT-1 to C2H2 or C2H4, while bands characteristic of hydrocarbon polymeric species were detected with C2H2/H2 deactivated catalysts. On each catalyst, the adsorbed carbon monoxide was found to exist in the linear form. From the experimental observations regarding the hydrogenation of acetylene in the presence of various pressures of [14-C] -ethylene and determination of the kinetics and product distribution, it has been established that the major route to ethane formation is via a route involving direct hydrogenation of acetylene, rather than via ethylene as an intermediate. The results have been interpreted in terms of the presence of separate surface sites for the hydrogenation of acetylene to ethylene, the hydrogenation of acetylene to ethane and for the hydrogenation of ethylene to ethane. From the kinetics and variations of the product compositions with the experimental variables for buta-1,3-diene hydrogenation, it has been proposed that, whilst 1:2 addition of hydrogen to the buta-1,3-diene was responsible for but-l-ene formation, 1:4 addition of hydrogen to buta-1,3-diene, rather than the isomerisation of but-l-ene, was responsible for the production of trans-but-2-ene and cis-but-2-ene