T.V. Prabhakar

Delft University of Technology, Delft, South Holland, Netherlands

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Publications (34)0.6 Total impact

  • N. Jose · N. John · P. Jain · P. Raja · T.V. Prabhakar · K.J. Vinoy
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    ABSTRACT: This work describes an ultra low power three chip system that harvests RF energy for sensing applications. The input RF power levels are typically lower than -6dBm. Our scheme uses two commercially available chips, a DC-DC boost converter and a low power microcontroller. In this paper we present the design of a third chip that compliments these to form a complete system. This chip includes an RF-DC rectifier, low power analog to digital converter (ADC) and a resistor emulation circuit (REC). While the REC helps in enhancing the efficiency of the boost converter, the ADC replaces the one present in the microcontroller and reduces the operating power requirements. The chip is designed in standard 0.18μm CMOS process technology.
    No preview · Article · Aug 2015
  • M.R. Rao · J. Kuri · T.V. Prabhakar
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    ABSTRACT: Demand Response is under implementation throughout the globe by many utilities to incorporate the end user as an active player in reducing supply-demand imbalances. Day-ahead pricing is provided as an option to schedule electric loads so as to take advantage of time-varying prices. However, user convenience is also a factor that must be taken into account, as users may be willing to forego some savings to reduce inconvenience. We formulate an optimal scheduling problem considering both aspects. As the search space is exponentially large, we propose two greedy algorithms to find good schedules. To assess performance, we obtain the optimal schedule via Markov Chain Monte Carlo (MCMC) based simulations. We apply the framework to two case studies; one study uses appliance energy profiles obtained by actual measurements using the Joule Jotter, a device designed and developed in-house. Results indicate that the proposed algorithms perform very well, achieving performance within 10%of the optimal.
    No preview · Article · Apr 2015

  • No preview · Conference Paper · Jan 2015
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    ABSTRACT: We undertake a step-by-step approach in the design of two Near Field Communication (NFC) products for pervasive healthcare monitoring. Our first product is an NFC based battery charger circuit to charge a thermometer equipped with wireless communication. Our system design has a simple linear charger, with overvoltage and undervoltage protection implemented as an android App. The NFC power source provides 13 − 15 mW of continuous power and is able to charge a 45mAH battery in about 10 hours from deep discharge to full charge state. Since the weight of the charger is about 3 grams and the size is about 2 cms in diameter, this product is useful for wearable sensor devices and provides a convenient way of recharging the batteries without the need for any connectors in the device. This allows devices to be hermetically sealed, besides enabling smaller form factors. The second product is an NFC based battery-less medical grade thermometer. To obtain the temperature of a single patient, a maximum of 10 seconds is sufficient to read the sensor value starting from placement of a smartphone over the product.
    Full-text · Conference Paper · Jan 2015
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    ABSTRACT: We present our ``Zero Energy Network'' (ZEN) protocol stack for energy harvesting wireless sensor networks applications. The novelty in our work is $4$ fold: (1) Energy harvesting aware fully featured MAC layer. Carrier sensing, Backoff algorithms, ARQ, RTS/CTS mechanisms, Adaptive Duty Cycling are either auto configurable or available as tunable parameters to match the available energy (b) Energy harvesting aware Routing Protocol. The multi-hop network establishes routes to the base station using a modified version of AODVjr routing protocol assisted by energy predictions. (c) Application of a time series called ``Holt-Winters'' for predicting the incoming energy. (d) A distributed smart application running over the ZEN stack which utilizes a multi parameter optimized perturbation technique to optimally use the available energy. The application is capable of programming the ZEN stack in an energy efficient manner. The energy harvested distributed smart application runs on a realistic solar energy trace with a three year seasonality database. We implement a smart application, capable of modifying itself to suit its own as well as the network's energy level. Our analytical results show a close match with the measurements conducted over EHWSN testbed.
    Full-text · Article · Apr 2014
  • V Sesha Raghav · Varun Gowtham · H.S Jamadagni · T.V Prabhakar
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    ABSTRACT: In the last few years, Power Line Communication (PLC) has gained momentum due to high data rate communication over existing power lines. The Home Plug AV (HPAV) and High Definition Power Line Communication (HD-PLC) are PLC specifications designed to provide 200 Mbps of PHY channel rate between hosts connected by modems operating at 2-28 MHz frequency range for home usage. A Logical Network (LN) formed by two or more modems allows communication with each other by sharing the same network key. With most of the world's population residing in Multi Dwelling Unit (MDU), there is high chance of unintentional interference among LNs assuming each unit of MDU owns an LN. In such a case, the channel bandwidth is shared among interfering LNs; thereby reducing combined throughput of all LNs. Considering LNs are given separate power line channels and operating on different phases, they may still undergo crosstalk if the power line channels are placed closer than a certain minimum separation. This paper suggests a method to maximize the combined throughput in a MDU keeping in view the LN interference. The solution also proposes a practical case of improving throughput between application servers situation in apartment blocks.
    No preview · Conference Paper · Jan 2014
  • H S Jamadagni · Varun Gowtham · N S Soumya · T V Prabhakar
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    ABSTRACT: We describe our novel LED communication infrastructure and demonstrate its scalability across platforms. Our system achieves 50 kilo bits per second on very simple SoCs and scales to megabits bits per second rates on dual processor based mobile phone platforms.
    No preview · Conference Paper · Jan 2014
  • T V Prabhakar · Soumya N S · Jamadagni H S
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    ABSTRACT: Physical layer security is one possible alternative for the exploding Internet of Things in the coming years. We advance the state of art in physical layer security by implementing self-jamming on ultra low power transceivers without the assistance of “friendly” nodes. The implementation supports flexible payload sizes; where the simplest implementation carries a full data payload. We consider a passive eavesdropper with varying attack potentials; constantly attempting to recover the original data from the transmitter. We show that a 3dB shift and transmit power control between transmitter and receiver is good enough to ensure data security. The key insights from this work is that large payloads have a 50% lower throughput compared to smaller payloads. Also smaller payloads have the advantage of a 25% delay performance improvement over large payloads.
    No preview · Conference Paper · Sep 2013
  • Gaurav Singh · Rahul Ponnaganti · T.V. Prabhakar · K.J. Vinoy
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    ABSTRACT: A circuit topology based on accumulate-and-use philosophy has been developed to harvest RF energy from ambient radiations such as those from cellular towers. Main functional units of this system are antenna, tuned rectifier, supercapacitor, a gated boost converter and the necessary power management circuits. Various RF aspects of the design philosophy for maximizing the conversion efficiency at an input power level of 15 μW are presented here. The system is characterized in an anechoic chamber and it has been established that this topology can harvest RF power densities as low as 180 μW/m2 and can adaptively operate the load depending on the incident radiation levels. The output of this system can be easily configured at a desired voltage in the range 2.2–4.5 V. A practical CMOS load – a low power wireless radio module has been demonstrated to operate intermittently by this approach. This topology can be easily modified for driving other practical loads, from harvested RF energy at different frequencies and power levels.
    No preview · Article · Jul 2013 · AEU - International Journal of Electronics and Communications
  • T. V. Prabhakar · H. S. Jamadagni · B. S. Sudhangathan
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    ABSTRACT: We describe the construction of a data mule platform running a set of services useful for small and marginal farmers. Firstly, farmers are provided information about their standing crop by instrumenting their farm lands with soil moisture sensors and measuring the associated water stress. The platform is also equipped with market prices, seed availability, latest farming practices, of pest and disease attacks, rainfall etc. Thus, the idea is to improve the livelihood of these farmers by useful information and creating an advice system so as to reap maximum benefits in terms of yield/harvest. The data mule acquires data from several sources such as: (a) soil moisture probes installed in an individual's farmland, (b) Retrieving market price and other information from official websites etc. The mule delivers the information to the farmers' mobile phones via Wi-Fi, free of cost. The data mule is powered to work by harvesting energy from bicycle dynamo and solar panel. A mobile application is developed for Android and for Symbian phones as well. The phones support local audio language for ease of use.
    No preview · Conference Paper · Apr 2013
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    ABSTRACT: Emotion recognition through physiological recording is an emerging field of research with many promising results. This work is involved in the construction of a device used to identify basic human emotions indexed by Electro Dermal Activity (EDA) in real time, using a non-invasive sensor attached to a wrist band. We refer to the system as "E Lock-Holmes". The device measures changes in Skin Conductance Level (SCL) caused due to stimulating signals from brain which results from sympathetic neural activity using Ag/AgCl electrodes placed on the ventral side of the distal forearm to evaluate the emotions of the user outside the constrained laboratory environment without interrupting the normal daily routine. The device consists of an embedded system for EDA signal acquisition and a wireless communication module to send processed EDA signals to a remote system. A vibrator attached to the device is used to provide user feedback.
    No preview · Conference Paper · Apr 2013
  • Conference Paper: Infinite Coffee Cup
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    ABSTRACT: Imagine you go to your favorite café house or a restaurant and the system recognizes your presence and alerts the waiter and caters to your favorite beverage you longed for the day. The main motivation to Infinite Coffee Cup is to detect the presence of a person and dynamically and non-Invasively estimate the amount of coffee in a circular cup on the table. One of the more popular devices used is Microsoft Kinect, which has cameras that capture both RGB and Depth data. Kinect is a low cost sensing device which provides two streams of images, 8 bit 3 channel RGB image and 11 bit single channel depth image. The system is fixed at the roof facing downwards and it takes a top view of the cup placed on the table. We use "libfreenect" [1] drivers which is an open source project, to stream data from kinect. We employ various image processing algorithms using Open CV (Open Source Computer Vision) which is a library of programming functions for real time computer vision. The algorithms are used to manipulate the data from kinect to, -Detect the circular coffee cups in the RGB image. -Overlay and correlate the depth values of cups in the depth image to get the height and amount of coffee in the cup.
    No preview · Conference Paper · Apr 2013
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    ABSTRACT: In this work we describe our novel design of an embedded hardware communication device. The hardware is designed generically, by taking an example of a Zig Bee green radio. Our hardware completely eliminates the problem of idle listening encountered by most "mote" class hardware. Lower layers can assume node synchronization and thus transmit a minimum sized preamble. The circuit has three radios, interconnected with an antenna switch. We use simple but intelligent software to switch between the radios. Since our calculated energy savings when compared to designs without wake-up is significant, the system has the viability to be powered using harvested energy.
    No preview · Conference Paper · Apr 2013
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    ABSTRACT: We propose energy harvesting technologies and cooperative relaying techniques to power the devices and improve reliability. We propose schemes to (a) maximize the packet reception ratio (PRR) by cooperation and (b) minimize the average packet delay (APD) by cooperation amongst nodes. Our key result and insight from the testbed implementation is about total data transmitted by each relay. A greedy policy that relays more data under a good harvesting condition turns out to be a sub optimal policy. This is because, energy replenishment is a slow process. The optimal scheme offers a low APD and also improves PRR.
    No preview · Conference Paper · Jan 2013
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    ABSTRACT: Energy harvesting (EH) is a major step in solving the critical issue of availability of energy for sensor nodes. However, it throws many challenges. The applications built on the sensor networks powered by EH need to adapt their operations yet serve the purpose. We propose a distributed smart application for a multihop sensor network and in general in the future Internet of Things (IoT) where a network node executes an optimal number of policies to minimize the difference between available energy and consumed energy (called residual energy) for the execution of an application policy . We formulate this as a multi-criteria optimization problem and solve it using linear programming Parametric Analysis. We demonstrate our approach on a testbed with solar panels. We also use a realistic solar energy trace with a three year database including seasonality. The smart application is capable of adapting itself to its current energy level as well as that of the network. Our analytical results show a close match with the measurements conducted over testbed.
    No preview · Conference Paper · May 2012
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    ABSTRACT: Near Field Communication (NFC), is an integration of Radio Frequency Identification (RFID) technology with mobile devices. NFC offers a quick and convenient method of interaction between humans and NFC enabled devices. Current research concerning NFC appears to mainly focus on development of NFC enabled applications and services. In this paper, we study the performance of NFC devices by considering metrics such as achieved data rates and received power for several distances. Knowledge of these metrics may be useful for application developers to build applications efficiently. We have developed various applications on NFC enabled devices for public transport systems. We also describe the design of 13.56 MHz antenna which was used for measurements of the received power.
    No preview · Chapter · Jan 2012
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    ABSTRACT: We investigate the queue stability in Energy Harvesting Sensor (EHS) nodes under indoor conditions wherein solar energy equipped EHS nodes are deployed for intrusion detection. We implement two policies, namely Throughput Optimal and Greedy and test the conditions under which they ensure queue stability. Energy and Data are injected following a distribution. An important observation is the use of “mean harvested energy” in proposed policies. Presently it does not seem practical to use this term, but works well when nodes have apriori knowledge of its value. Our results indicate that exponential arrival of data and energy offers maximum stability under these stressful conditions.
    No preview · Article · Jan 2012
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    ABSTRACT: With the growing dependence on the wireless sensor devices, it is imperative that power supply to them and their energy usage has acquired centre stage. Energy harvesting is one possible remedy. To enhance the use of devices that are using harvested energy, many novel schemes need to be devised. In this paper we propose four throughput enhancement schemes with a wide range of applicability to energy harvesting wireless sensor networks. The schemes are designed by taking into consideration available resources in the nodes as well as the energy harvesters that are used to drive the sensor nodes. All the four schemes are implemented, evaluated and compared for their performances. We present schemes from simple naive scheme which is of low complexity, to probabilistic probing scheme which incorporates advanced methods to appropriately use the harvested energy. All the schemes require minimum system resources and sufficient harvested energy before starting communication. Moreover, when the harvested energy varies due to the changes in the environment and characteristics of wireless channel varies, we found that truncated channel inversion with power control is the appropriate scheme. This article provides a thorough step by step discussion on the implementation of maximizing communication throughput in energy harvesting sensor nodes under varying environment. We also provide some insights into energy requirements for a multi-node network.
    No preview · Conference Paper · Jan 2012
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    ABSTRACT: We implement two energy models that accurately and comprehensively estimates the system energy cost and communication energy cost for using Bluetooth and Wi-Fi interfaces. The energy models running on a system is used to smartly pick the most energy optimal network interface so that data transfer between two end points is maximized.
    No preview · Conference Paper · Jan 2012
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    ABSTRACT: To overcome the problem of unavailability of grid power in rural India, we explore the possibility of powering WSN gateways using a bicycle dynamo. The "Data mule" bicycle generates its own power to ensure a self sustainable data transfer for information dissemination to small and marginal farmers. Our multi-interface WSN gateway is equipped with Bluetooth, Wi-Fi and GPRS technologies. To achieve our goal, we exploit the DTN stack in the energy sense and introduce necessary modifications to its configuration.
    Preview · Article · Jul 2011