E-DTN : A Multi-Interface Energy DTN Gateway

arXiv:1107.3294v1 [cs.NI] 17 Jul 2011 E-DTN : A Multi-Interface Energy DTN Gateway Prabhakar T.V, Akshay Uttama Nambi S.N, Jamadagni H.S Centre for Electronics Design and Technology, Indian Institute of Science, Bangalore, India (tvprabs,akshay,hsjam)@cedt.iisc.ernet.in 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. Index Terms—ICTs, Agriculture, Bicycle dynamo, Energy Harvesting, DTN, WSNs, Wi-Fi, Bluetooth. I. INTRODUCTION Several gateway technologies exist today to relay data aggregated from an ad-hoc sensor network cluster. Such tech- nologies include Bluetooth, Wi-Fi, and GSM/GPRS. While GPRS has the added advantage of relaying the data directly to the Internet, Bluetooth and Wi-Fi can be used to relay data over short to medium range respectively. One deterrent to the wide-spread use of such technologies in the rural context comes from the fact that most villages in India have very little access to grid power. Often power cuts last for 12-16 hours a day. GPRS technology requires sufficiently high energy with peak currents of about 1.6A during data transmissions. Even large battery backups are insufficient to guarantee its continuous operation. Is there a solution to this problem? Can we generate power just sufficient for GPRS transmission? Our work positions itself to tackle the issue of powering the GPRS gateway from harvested energies. Fig.1 shows the block diagram of E-DTN multi-interface gateway. Alongside are shown sensor network gathering data in the field and other embedded devices such as camera phones and data modems. In the agriculture context, the purpose of a sensor network deployment is to collect data to provide information to small and marginal farmers about the standing crop by evaluating its stress in adverse situations such as drought and pest attacks that impact the yield. The requirement for data gateway is to relay data for the purpose of analysis and decision science. II. GOAL AND RELATED WORK Our goal is to demonstrate the capabilities of a grid inde- pendent hybrid data relay communication system comprising of Bluetooth, and Wi-Fi. GPRS technology is used as the Internet gateway. We use a bicycle dynamo to generate this energy. In this energy generating system, data downloads are possible over Wi-Fi or Bluetooth, and upload to Internet uses GPRS technologies. Since energy is generated on the Fig. 1. Block diagram of E-DTN multi-interface. fly, it now becomes necessary to negotiate this quantity. In our work, we employ the Delay/Disruption Tolerant Network (DTN) stack and exploit its features from the view of energy availability rather than connectivity and we therefore call our system “E-DTN”. In [1] the authors discuss an energy driven system to improve packet delivery in a sparse sensor deployment. In this work, we adapt packet buffering and propose an algorithm towards an energy based data transfer, where data bundles are exchanged between E-DTN end points to match the minimum energy available between the node pairs. Thus our scheme is comprehensive compared to [1]. Using E-DTN, energy availability in terms of “energy bundles” is negotiated. The input parameters considered for negotiation include: (a) energy availability (b) data rate (c) transmit power and finally (d) channel state based on signal strength. The outcome determines the data transfer either over Bluetooth or Wi-Fi. We show that energy stored in a super capacitor is sufficient for our purpose. III. IMPLEMENTATION The initial latency for the energy bundle transfer is 6 sec- onds from the time the Data mule (DM) and Field Aggregation Node (FAN) estimate their energies. We implemented the Data mule using Gumstix’s system on module (SOM) Overo Fire as the controller, and Siemens TC65 as the GPRS module. Table I shows the split time and energy break-up for a single bundle transfer. The data mule consumes around 190s and 360J for a bundle transfer using DTN over Wi-Fi to download the data from FAN and GPRS for uploading the bundle to the server. Fig.2 shows these system components including the super capacitor banks for storing the energy. 978-1-4244-8953-4/11/$26.00 c⃝2011 IEEE Fig. 2. Dynamo Driven Data mule. Fig. 3. Energy per packet vs Buffer size for 95% Confidence Interval Table II shows the latency in a single bundle transfer between the E-DTN end points over Bluetooth and Wi-Fi. We experi- mentally evaluated the optimal size of the GPRS buffer. The packet size was fixed at 32 bytes. Experiments were conducted by varying the buffer size and programming

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