High-frequency techniques are applied to analyze and optimize radio localization systems in indoor scenarios. The localization estimate of a mobile station is obtained using the fingerprint technique. The fingerprint of a point is a vector whose terms are the field strengths of the signal received from a network of fixed base stations. The location algorithm is based on minimizing the Euclidean distance between the fingerprint of the unknown point and the fingerprints of a mesh of reference points. Traditionally the fingerprints (stored in a database) of the reference points are obtained by measurement. Here, we propose obtaining these data by using deterministic Geometrical Theory of Diffraction (GTD) models. The model considers multiple bounces and the transmission through indoor walls and also the scattering from furniture in order to obtain a reliable database for the problem. Using the GTD model, the localization system is simulated in two indoor scenarios with different parameters. The proposed procedure based on a GTD model appears well suited for the design and optimization of localization systems tailored to specific scenarios and avoids large and costly measurement campaigns. Several results and conclusions are presented that illustrate these points.