In many mobile wireless applications, such as automated automobile driving, flight training for unmanned aerial vehicles, and location of sources or target tracking with wireless sensor networks, it is more important to know the exact relative locations of the nodes than their Absolute coordinates. GPS, the most ubiquitous location system available, generally only provides absolute coordinates. In addition, low-cost receivers can present tens of meters of error or worse in challenging RF environments. This project is developing an approach that uses GPS to obtain information regarding the location of multiple receivers. Nodes in a network share their raw satellite measurements and use this data to track the relative movements of neighboring nodes instead of calculating their own absolute coordinates. The system has been implemented using an Android phone network equipped with custom Bluetooth headsets and an integrated GPS chip to provide raw measurement data. Our evaluation shows that the accuracy of monitoring in centimeter scale at a refresh rate of 1 Hz is possible under various conditions with the technique. This is more than an order of magnitude more accurate than simply taking the absolute coordinate difference from reported nodes or other simplistic approaches due to the presence of uncorrelated measurement errors.