Navigation Using Signals of Opportunity in the AM Transmission Band

摘要

Maintaining a precision navigation solution both in a GPS hostile jamming environment and also in a GPS non-compatible terrain area is of great importance. To that end, this thesis evaluates the ability to navigate using signals from the AM band of the electromagnetic spectrum (520 to 1710 kHz). Navigation position estimates are done using multi-lateration techniques similar to GPS. However, pseudoranges are created using Time Difference of Arrival (TDOA) distances between a reference receiver and a mobile receiver, allowing the mobile receiver to obtain absolute position estimates over time. Four methods were developed for estimating the cross-correlation peak within a specified (sampled) portion of the cross-correlation data for use in TDOA measurement generation. To evaluate the performance of each peak locating method, a simulation environment was created to attempt to model real-world Amplitude Modulation (AM) signal characteristics. The model simulates AM transmission sources, signal receivers, propagation effects, inter-receiver frequency errors, noise addition, and multipath. When attempting to develop a data collection system for real-world signals, it became clear that selecting a proper analog front-end prior to digitization is pivotal in the success of the navigation system. Overall, this research shows that the use of AM signals for navigation appears promising. However, the characteristics of AM signal propagation, including multipath, need to be studied in greater detail to ensure the accuracy of the simulation models.