Protocol Considerations to Improve the Reliability of Data Collection in a Radio Telemetry System

In collaboration with Clermont County, the U.S. EPA's Office of Research and Development is developing watershed-wide load and transport models to account for stream processes at the Experimental Stream Facility (ESF) in Milford, Ohio. To better understand environmental stressors in stream flow and the structure and function of stream ecosystems, researchers are establishing continuous water quality monitoring stations along the Lower East Fork River and its tributaries. River and stream water quality are being automatically monitored and recorded every few minutes for: temperature, pH, dissolved oxygen, conductivity, stream flows (light levels, temperature and humidity), weather conditions (rainfall, solar radiation, temperature, humidity and barometric pressure) using remote sensors and weather stations. To transfer water quality data back to the ESF, high frequency data linking is being investigated for reliably and cost effectiveness. EPA and the University of Cincinnati are examining the existing data telemetry software and suggesting a change in transmission protocol. The new protocol offers two important features: a built in CRC-16 for error correction and the ability to use the station as a digital repeater. Use of a protocol with a CRC will yield many benefits; the quality of transmitted data will be improved thus allowing the system to utilize higher baud rates, which translates into shorter transmission times and power savings. Use of the new protocol does incur additional packet length to accommodate addressing and the CRC as well as additional computational effort to validate incoming data by computing the CRC, so a comparison of protocols is merited. Also discussed are the benefits of `digipeating' — by allowing each station to act as an addressable repeater transmissions can be broadcast over several hops to extend the range beyond simplex distance with the ultimate goal of meeting the 50 mile specification, though this is subject to the additional considerations of station density and use of directional antennas. Because each station is given a unique address there are possibilities for routing and redundancy in future projects