The purpose of the GPS Locator Drifter Buoy project is to improve a current drifter buoy system to meet the specified requirements. The project will provide experience in system design and the opportunity to learn about the Global Positioning System (GPS), the Very High Frequency (VHF) band, and other technologies involved with wireless communications. This project was completed on behalf of the private company A.G.O. Environmental Electronics Ltd. for the Coastal Geoscience Research Corporation.
The following sections contain general background information on the original buoy system in order to provide a better understanding of this project.
The Original Design
The GPS locator drifter buoy will be used to monitor the water currents near sewage outflows. A.G.O. Environmental Electronics Ltd. designed a prototype GPS locator drifter buoy to follow the currents off the coast of Victoria and send out GPS transmissions containing time and location information to be logged at the receiving end. The original prototype used a GPS module and microcontroller to transmit the data at 433 MHz in the UHF band. The reason such a high frequency was used was because this band is not licensed. The diagram below shows the basic features of the system.
After the original field tests, it was discovered that the transmission range was limited to about 500m, which was not sufficient. This was because of the low transmission power (only ~5W) and the cancellation effects at this high frequency. The direct signal to the receiving boat would be cancelled by a signal that bounced off the waves. This is called the “beach ball effect” or, more technically, the Fresnel Effect. A second problem was that the original whip antenna was not strong enough so when deployed on the ocean, it broke off. Because of these problems, it is clear that the transmission system needed to be redesigned.
The client set out the following specifications for the drifter buoy:
In order to meet all of the requirements listed above and solve the problems with the current system, a few solutions have been proposed. First, in order to extend the transmission range, the system will be modified to transmit at a lower frequency in the VHF band. To do this, a new VHF transmitter will have to be chosen and the microcontroller changed to configure the GPS module differently. To ensure that the batteries in the buoy last long enough, transmission will only occur every set interval of time. This also has to be programmed into the microcontroller. Also, the antenna mounting will need to be fixed so that it will be stronger. Lastly, research into whether a better GPS module with more functions would improve the system.