| Many of today's wireless mobile applications rely heavily on highly accurate node location information. For outdoor applications, GPS is regarded as the clear choice for location determination, especially as its price and power requirements steadily decline; however, a significant tradeoff exists between cost and accuracy. Low-cost receivers, such as those found in smartphones and other handheld devices, can exhibit large errors on the order of tens of meters, especially in challenging RF environments such as wooded areas or urban centers. Higher quality devices exist that can provide much better accuracy, but they come at the expense of increased price, with commercial-grade surveying equipment costing thousands of dollars while requiring extensive setup and calibration before becoming usable.;GPS enjoys widespread applicability in the positioning domain due to its unique ability to simultaneously service an infinite number of users, providing absolute coordinates anywhere on Earth. The caveat is that many applications, including typical wireless sensor network (WSN) deployments, do not need precise absolute locations. In fact, a large percentage of WSN localization methods rely on estimating the range between nodes to derive their locations in a relative coordinate system. There also exist numerous applications beyond WSNs that require accurate relative locations, including autonomous driving, collision avoidance, land surveying, precision agriculture, and formation flying of unmanned aerial vehicles (UAVs), among others. Today's solutions to these types of problems involve post-hoc manipulation of absolute GPS coordinates (e.g. Differential GPS) or the use of additional sensors, such as LIDAR, accelerometers, or gyroscopes, which tend to be very costly.;This dissertation aims to bridge the gap between cost and accuracy by presenting a novel relative localization system based on the ubiquitous U.S.-based Global Positioning System and only low-cost, single-frequency GPS receivers. The goal is to enable commercial receivers to achieve an unprecedented centimeter-scale level of accuracy for applications that require node locations in a relative coordinate frame. Such an increase in GPS accuracy (in the relative sense) without a corresponding increase in cost should enable the production of novel applications that are either not economical today or have proven to be out of reach given the current state of the art. |
