Abstract : The fundamental objective of this research project is to improve the GPS receiver performance when subjected to strong nonstationary interference. The techniques applied and proposed to achieve this objective rely on the estimation of both time-frequency and spatial signatures of the jammers. The report consists of four chapters addressing important problems in nonstationary interference mitigation in GPS receivers. The first two chapters deal with a single antenna receiver, whereas the last two chapters consider the presence of multi-antenna array. In all four chapters, the nonstationary interference is cast as an FM signal and it is mitigated using its temporal and spatial characteristics through subspace projection methods. The first three chapters are GPS specific and utilize the GPS signal structure and its deterministic nature. Chapter 4 applies to the general problem of suppressing instantaneous narrowband signals in broadband communication platforms.