Empirical measurements on a wireless sensor network
My project was to develop a hardware and software platform consisting of client nodes and a base station interconnected wirelessly. The nodes collect physical data for their local environment - I implemented a temperature measurement and a battery level reading. These measurements were placed in a packet which was then relayed via other nodes to the base station. The base station is attached to a USB dongle to a computer which collects the data and stores it into a log file for later analysis.
In designing such a network, my goal was to learn about routing protocols, take key concepts learned in classes, such as different modulation schemes and the study of wireless degradation in various environments due to reflections and interference, and explore an implementation of a commercial wireless system. Such a system could be modified to fit a multitude of applications such as environmental data collection for farmers, low power networks for data communication for disaster recovery teams, or sensor networks or implemented in a house to collect data over long period and analyze variances in different regions and implement automated control through a feedback loop.
To implement my code, I used TI’s EZ430-RF2500. This development kit contains the TI MSP430F2274, a 16MHz, 16 bit RISC processor which in active mode only pulls 270µA. The MSP430F2274 is coupled with a TI CC2500 which is a 2.4GHz RF transceiver used to communicate with the other devices. The EZ430-RF2500 connects to the computer via a USB dongle with proprietary firmware loaded which allows for programming and serial communication with the computer.
I built a network using three devices; one connected to a laptop acting as the access point and two remote devices powered by two AAA batteries acting as the end devices or clients. I performed a study of packet success rates in different environments, specifically inside a residential home, outside in a residential neighborhood and in a rural area. In close ranges (distances less than 50’) there were no noticeable differences in performance between the three environments. I could not exceed 50’ inside the residential environment due to the size of the tested house. Beyond 50’ in the two outside environments, the results surprisingly did not differ greatly; successful transmissions were accomplished at distances only 10’ further in Town Lake; that is that successful transmissions were capable up to 95’ at Town Lake and 85’ in my uban neighborhood. As a representative finding, in the urban environment, the clients were successfully transmitting at an 80% success rate at 80’ pulling 84.48mW (26.4mA at 3.2V) while transmitting with 2-FSK.