【正文】 r, the researchers also need to monitor the environment in which the animal dwells and grazes. Sensors for measuring the temperature, humidity, and light as well as animal activity are embodied in the system. Data Transmission and Recovery: To collect the dispersed data for analysis by the researchers, it needs to be transmitted to the base station(s). Since the Barasingha has a fairly large movement track it is not possible to equip the entire region with numerous base stations. To address this issue, the data needs to be moved through the network, employing node to node munications as was attempted in Zebranet[2]. In order to pensate for high latency, the node has a large external flash to acmodate data generated on the node as well as acquired through peer interaction. Section discusses the munication in more detail. Energy harvesting: The nodes need to be alive for a minimum of a year, tracking the migration path, avoiding any human intervention. Their only contact is the wireless link with other nodes or the base station as the case may be. Also, since there is a limitation on the weight of the node, a bulky power supply is forbidden. Hence, the node needs to have lightweight power back up system. Given that the animal will mostly be in large fields under open skies, the required power supply could be equipped with solar energy harvesting features. With careful energy management policy, supplemented by harvesting, the energy requirements can be easily met. The power supply is discussed in more detail in Section III. System Overview Broadly the wildCENSE system is divided as in Figure 1, namely the hardware, related system software and drivers, middleware servers with data logging and web hosting services and finally the browser based visualization software. 1) Hardware Architecture The plete sensor node along with the battery recharging system is in the form of a collar to be worn by the animal. Hardware system architecture of wildCENSE node is as depicted in Figure 2. The design issues as discussed in Section 2 have been carefully met. Each ponent has been carefully selected based on earlier prototypes to meet accuracy, power, voltage patibility and cost considerations [6]. The ponents that make up a single node are as follows:Microcontroller – ATMega1281V [7], with 128K bytes program memory, is the core processing unit of our design. It has 4K bytes of EEPROM and 8K bytes of SRAM. The availability of 2 USART ports enables independent Figure 1. wildCENSE System Overviewmunication of GPS and Radio transceiver with the core processing unit simultaneously. This allows us to remove the multiplexing overhead as described in the software section . The internal resonator is not accurate enough for serial munication, so an external crystal of MHz is used. (limiting baud error to zero percent [7]). Real Time Clock DS3231 [8] For node discovery, all the nodes need to wake up at the same time requiring them to be synchronized. External RTC is required to accurately synchronize these nodes. It also generates periodic interrupts to wake up the microcontroller from its “Power Down” sleep mode. Features like extreme accuracy, integrated temperature pensated crystal oscillator (TCXO), I2C interfacing at different baud rates make the device ideal for this application. Any mismatch in the time in the system (between two interacting nodes) can cost a lot of power in network synchronization. RTC running on different nodes are skewed due to the environment. To maintain the accuracy of node to node munications, the RTC is synchronized by the GPS device every five days, keeping the clock skew within 1 sec. GPS – Lassen iQ GPS Receiver with antenna [9] – It has a small footprint, low energy consumption (89mW at ) in active mode. To achieve high accuracy, it uses twelve processing channels to track the GPS satellite signals. Lassen iQ GPS supports the required NMEA protocol with GPRMC message format, which contains all the required information namely date, latitude, longitude and time. It serially municates with the microcontroller at 4800 bps. Our GPS is used in On/Off mode since readings are taken every 3 hours. To utilize “Warm start” feature of GPS, we use a battery backup mechanism. Radio Transceiver – XBeePro [10] This DigiKey munication module is based on ZigBee/IEEE standard. It operates at (only freely available ISM band in India), providing a range of more than a kilometer. While using this frequency results in higher power consumption for same range pared to 900 MHz, we gain in terms of much higher data rate and smaller pact antenna. Low cost, low power and ease of use are among the other advantages. It also provides five sleep modes to meet various needs of different applications. We use lowest power sleep mode as it is not a time but power critical system. Delay of few milliseconds of wake up are well within the system’s toleranceFigure 2. wildCENSE Hardware setup depicting various ponents, their interfacing and power supply. Memory – ATMEL AT45DB16B Data flash [11] A high memory storage is required to plement the long latency of munication between the base and the node. For our WSN, a node needs to collect data from its peers, asking for a higher memory capacity. AT45DB16B, with SPI interfacing looks quite promising for the scenario. An operational inhouse developed file system [12], based on UCBs Matchbox file system [13], is being used, which makes the storage system simple and efficient. Addit