Indoor self-localization of the mobile robot is an important function to achieve tasks such as exploring the building or carrying products in the factory. Although there are many methods to achieve this, most of them face tradeoffs between estimation precision and calculation cost. Previously, we have proposed low-calculation-cost self-localization method for mobile robot using microphone array and ambient sounds as a landmark. Since this method only utilizes sound signals, it requires less calculation resource as a previous precise method which uses cameras or laser range finders, and it can be applied to estimate the robot location with less calculation cost. Although the layout of the sound sources will affect to the self-localization, the relation between them have not unveiled. In this paper, the relation between the condition number, C, which represents the sound sources layout, and the error of self-localization method in two-dimension for mobile robot using microphone array were examined by numerical experiment. The numerical experiment was conducted with 3 sound sources, which were arranged in a 4 m diameter circle, and one robot run on a 2 m diameter circular trajectory. There were 4 conditions to examine the spec and limitation of the estimation method. From the results, it was confirmed that the estimation error of self-localization using DOAs is affected by C. The result indicates that less 1/C lead to a worse estimation error. Additionally, C depends on the sound sources layout such as the location and number of the sound sources. These results indicate that the sound sources layout affects to the accuracy of the self-localization and the distribution of C. From these, the sound sources layout could be evaluated by the value of C.
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