The suitability of FM radio receivers for automotive applications has conventionally been evaluated by evaluating the reception characteristics of broadcast waves while conducting repeated driving tests in a special test environment. Because the evaluation of sound quality while driving relies upon the auditory judgment of a limited range of test subjects, these tests present issues in terms of the reproducibility and objectivity of the evaluations.
In order to resolve these issues, a method of evaluating the suitability of FM receivers for automotive applications through the creation of a virtual radio wave environment on a PC was developed (this has been termed the “Two-Stage method”).
In the research described in this paper, the Two-Stage method was used to analyze the effect of multipath distortion on FM receivers when driving through arbitrary radio wave propagation environments. In order to quantify the effect of multipath distortion, the multipath distortion rate was defined as an index of sound quality evaluation while the vehicle is in motion.
Employing the multiple signal classification (MUSIC) method made it possible to estimate the characteristics of the arbitrary radio wave propagation environment such as number, arrival direction, and delay time of incoming waves for the first time.
By generating the results of these estimations in the Two-Stage method, it was possible for the first time to compare the suitability for vehicle fitting of FM diversity receivers and non-diversity receivers, and to compare suitability for vehicle fitting based on differences in the directivity of vehicle-mounted FM antennas.
