Energy Sharing for Multiple Sensor Nodes with Finite Buffers

We consider the problem of finding optimal energy sharing policies that maximize the network performance of a system comprising of multiple sensor nodes and a single energy harvesting (EH) source. Sensor nodes periodically sense the random field and generate data, which is stored in the corresponding data queues. The EH source harnesses energy from ambient energy sources and the generated energy is stored in an energy buffer. Sensor nodes receive energy for data transmission from the EH source. The EH source has to efficiently share the stored energy among the nodes in order to minimize the long-run average delay in data transmission. We formulate the problem of energy sharing between the nodes in the framework of average cost infinite-horizon Markov decision processes (MDPs). We develop efficient energy sharing algorithms, namely Q-learning algorithm with exploration mechanisms based on the $\epsilon$-greedy method as well as upper confidence bound (UCB). We extend these algorithms by incorporating state and action space aggregation to tackle state-action space explosion in the MDP. We also develop a cross entropy based method that incorporates policy parameterization in order to find near optimal energy sharing policies. Through simulations, we show that our algorithms yield energy sharing policies that outperform the heuristic greedy method.Comment: 38 pages, 10 figure

H2B: Heartbeat-based Secret Key Generation Using Piezo Vibration Sensors

We present Heartbeats-2-Bits (H2B), which is a system for securely pairing wearable devices by generating a shared secret key from the skin vibrations caused by heartbeat. This work is motivated by potential power saving opportunity arising from the fact that heartbeat intervals can be detected energy-efficiently using inexpensive and power-efficient piezo sensors, which obviates the need to employ complex heartbeat monitors such as Electrocardiogram or Photoplethysmogram. Indeed, our experiments show that piezo sensors can measure heartbeat intervals on many different body locations including chest, wrist, waist, neck and ankle. Unfortunately, we also discover that the heartbeat interval signal captured by piezo vibration sensors has low Signal-to-Noise Ratio (SNR) because they are not designed as precision heartbeat monitors, which becomes the key challenge for H2B. To overcome this problem, we first apply a quantile function-based quantization method to fully extract the useful entropy from the noisy piezo measurements. We then propose a novel Compressive Sensing-based reconciliation method to correct the high bit mismatch rates between the two independently generated keys caused by low SNR. We prototype H2B using off-the-shelf piezo sensors and evaluate its performance on a dataset collected from different body positions of 23 participants. Our results show that H2B has an overwhelming pairing success rate of 95.6%. We also analyze and demonstrate H2B's robustness against three types of attacks. Finally, our power measurements show that H2B is very power-efficient

Sensor Selection and Random Field Reconstruction for Robust and Cost-effective Heterogeneous Weather Sensor Networks for the Developing World

We address the two fundamental problems of spatial field reconstruction and sensor selection in heterogeneous sensor networks: (i) how to efficiently perform spatial field reconstruction based on measurements obtained simultaneously from networks with both high and low quality sensors; and (ii) how to perform query based sensor set selection with predictive MSE performance guarantee. For the first problem, we developed a low complexity algorithm based on the spatial best linear unbiased estimator (S-BLUE). Next, building on the S-BLUE, we address the second problem, and develop an efficient algorithm for query based sensor set selection with performance guarantee. Our algorithm is based on the Cross Entropy method which solves the combinatorial optimization problem in an efficient manner.Comment: Presented at NIPS 2017 Workshop on Machine Learning for the Developing Worl

Rateless codes-based secure communication employing transmit antenna selection and harvest-to-jam under joint effect of interference and hardware impairments

In this paper, we propose a rateless codes-based communication protocol to provide security for wireless systems. In the proposed protocol, a source uses the transmit antenna selection (TAS) technique to transmit Fountain-encoded packets to a destination in presence of an eavesdropper. Moreover, a cooperative jammer node harvests energy from radio frequency (RF) signals of the source and the interference sources to generate jamming noises on the eavesdropper. The data transmission terminates as soon as the destination can receive a sufficient number of the encoded packets for decoding the original data of the source. To obtain secure communication, the destination must receive sufficient encoded packets before the eavesdropper. The combination of the TAS and harvest-to-jam techniques obtains the security and efficient energy via reducing the number of the data transmission, increasing the quality of the data channel, decreasing the quality of the eavesdropping channel, and supporting the energy for the jammer. The main contribution of this paper is to derive exact closed-form expressions of outage probability (OP), probability of successful and secure communication (SS), intercept probability (IP) and average number of time slots used by the source over Rayleigh fading channel under the joint impact of co-channel interference and hardware impairments. Then, Monte Carlo simulations are presented to verify the theoretical results.Web of Science217art. no. 70

Electrochromic properties of spiropyran-terthiophene adaptive polymers

Adaptive materials have the ability to modify their behaviour or characteristics in response to external stimuli, for example through electrochemical changes, macroscopically in the molecular structure. These materials may have only one form with binding skills whilst others are passive. In principle this material can be switched ‘on’ and ‘off’ using external stimuli [3]. In this field hybrid Polythiophenes substituted with Spiropyrans are an important representative class of conjugated polymers that form environmentally and thermally stable materials and stimulate deep interest for their optoelectronic and reversible properties. An enhancement in the electronic and photonic properties of the materials and the creation of new functions, such as new sensory materials or new biocompatible structures, critically depends on the synthesis of polythiophene [1,4]. This problem can be bypassed with some synthetically procedures that have been developed by our group and published on previous outputs. In this work the new family of hybrid spiropyran-terthiophenes moieties has been fully characterized and analyzed. An important aspect emerged in the study consists is the charge transfer during the processes of activation and deactivation of the material [2]. It has been observed spectroelectrochemically that a consistent charge transfer occurs while the activated surface is stimulated with an external potential. The kinetics of activation and deactivation has been detected at different potentials. This plays a remarkable role in the complete description of the properties of the structure under different conditions, especially during the electrochemical activation of the material in an electrolytical cell. This offers the possibility of inducing dramatic changes to the bulk properties of the active system by electrochemical stimulus. Herein we present the electrochemical and spectrelectrochemical behaviour of our materials. BIBLIOGRAPHY 1. S. Gambhir, K. Wagner, D. L. Officer, Towards functionalised terthiophene-based polymers. Synthetic Metals 154, 2005: 117-120. 2. S. Hammes-Schiffer, A. V.Soudakov. Proton-coupled electron transfer in solution, Proteins and electrochemistry. Journal of Physical Chemistry B, 2008, 14108-14123. 3. A. Radu, S. Scarmagnani, R. Byrne, C. Slater, K. T. Lau, D. Diamond, Photonic modulation of surface properties: a novel concept in chemical sensing. Journal of Physics D: Applied Physics, 40, 2007, 7238-7244. 4. H. Mehenni, L. H. Dao, Synthesis and characterization of novel conducting homopolymers based on β-styryl terthiophene. Canadian Journal of Chemistry, 86, 2008, 1010-1018

Interactive Joint Transfer of Energy and Information

In some communication networks, such as passive RFID systems, the energy used to transfer information between a sender and a recipient can be reused for successive communication tasks. In fact, from known results in physics, any system that exchanges information via the transfer of given physical resources, such as radio waves, particles and qubits, can conceivably reuse, at least part, of the received resources. This paper aims at illustrating some of the new challenges that arise in the design of communication networks in which the signals exchanged by the nodes carry both information and energy. To this end, a baseline two-way communication system is considered in which two nodes communicate in an interactive fashion. In the system, a node can either send an "on" symbol (or "1"), which costs one unit of energy, or an "off" signal (or "0"), which does not require any energy expenditure. Upon reception of a "1" signal, the recipient node "harvests", with some probability, the energy contained in the signal and stores it for future communication tasks. Inner and outer bounds on the achievable rates are derived. Numerical results demonstrate the effectiveness of the proposed strategies and illustrate some key design insights.Comment: 29 pages, 11 figures, Submitted in IEEE Transactions on Communications. arXiv admin note: substantial text overlap with arXiv:1204.192